Sleep disorders in Down syndrome: a systematic review

Sleep disorders are commonly observed in children with Down syndrome (DS) and can lead to significant behavioral and cognitive morbidities in these individuals.

Objective:

To perform a systematic review evaluating sleep disorders in individuals with DS.

Methods:

Search strategies were based on combinations of keywords: “Down syndrome”; “trisomy 21”; “sleep disorders”; “dyssomnias”; “sleep apnea”; “obstructive”; “sleeplessness”; “insomnia”; “parasomnias”; and “excessive daytime sleepiness”. PubMed and Science Direct were used. Only original studies and retrospective reviews in English published between January 2011 and March 2021 were included.

Results:

52 articles were included, most of them involving children and adolescents under 18 years of age. The main sleep disorder associated with DS was obstructive sleep apnea (OSA). Some studies reported the presence of cognitive dysfunction in patients with DS and sleep-disordered breathing, and few have been found about parasomnia, insomnia, and daytime sleepiness in these patients. Movement disorders and unusual postures during sleep may be related to disordered sleep breathing in DS. The main treatment options for OSA are continuous positive airway pressure therapy (CPAP), surgery, and weight control. Computational modeling associated with MRI has been used to plan surgical interventions in these patients.

Conclusions:

Individuals with DS are at high risk of developing sleep-related breathing disorders. The main sleep disorder associated with DS was OSA. The presence of sleep-disordered breathing contributes to a worsening of cognitive function in patients with DS.

Keywords:
Down Syndrome; Sleep Wake Disorders; Sleep Apnea Syndromes

Author/year	Study	N° of patients	Mean age (years/months)	Time of follow up	Outcome	Conclusion
Carvalho et al., 2020⁴⁹49 Carvalho AA, Amorim FF, Santana LA, de Almeida KJQ, Santana ANC, Neves FAR. STOP-Bang questionnaire should be used in all adults with Down syndrome to screen for moderate to severe obstructive sleep apnea. PLoS One. 2020 May;15(5):e0232596. http://doi.org/10.1371/journal.pone.0232596 http://doi.org/10.1371/journal.pone.0232...	Case series-Questionnaires; blood county	60 (DS)	>18 years	-	Adults with DS have a very high prevalence of OSA. Hematocrit levels, STOP-Bang questionnaires (SBQ) showed a strong correlation with OSA severity. The SBQ performed well in identifying moderate to severe OSA in this population.	Considered together, these results point to the need to perform OSA screening in all adults with DS, and STOP-Bang may play a role in this screening.
Capone et al., 2013³⁸38 Capone GT, Aidikoff JM, Taylor K, Rykiel N. Adolescents and young adults with Down syndrome presenting to a medical clinic with depression: co-morbid obstructive sleep apnea. Am J Med Genet A. 2013;161A(9):2188-96. https://doi.org/10.1002/ajmg.a.36052 https://doi.org/10.1002/ajmg.a.36052...	Case Control-PSG; Reiss and ABC scales	37 (9C) (28 DS)	19.8 (C) 21 (SD) years	5 years	– 86% of DS cases had OSA compared with 44% of controls; – Moderate-severe OSA was present in 54% of DS compared to 11% of controls; – Intermittent sleep-associated hypoxia and REM sleep deficits were also more frequent in DS. Across all subjects, prior tonsillectomy was not related to the presence or absence of OSA.	The results of the study suggest that OSA is a common comorbidity in adolescents and young people with DS and depression.

Author/year	Study	N° of patients	Mean age (years/months)	Time of follow up	Outcome	Conclusion
Wijayaratne et al., 2021⁴⁸48 Wijayaratne PR, Williams K, Davey MJ, Horne RSC, Nixon GM. Factors associated with referral for polysomnography in children with Down syndrome. Sleep Med. 2021 Jun;82:29-36. http://doi.org/10.1016/j.sleep.2021.03.019 http://doi.org/10.1016/j.sleep.2021.03.0...	Case series-BMIZ score; sleep symptoms questionnaires	64 (DS)	3–19 years	-	Despite not being referred for clinical sleep assessment, 42% of children with DS recruited from the community had moderate/severe OSA.	There were no differences in the quality-of-life behavior, daytime functioning, and sleep symptom questionnaires although the clinical group had a higher body mass index (BMI Z score) and overt signs of obesity. These results highlight the importance of PSG screening in all children with DS.
Caloway et al., 2020⁶³63 Caloway CL, Diercks GR, Keamy D, de Guzman V, Soose R, Raol N, et al. Update on hypoglossal nerve stimulation in children with down syndrome and obstructive sleep apnea. Laryngoscope. 2020 Apr;130(4):E263-E267. https://doi.org/10.1002/lary.28138 https://doi.org/10.1002/lary.28138...	Case series (Hypoglossal nerve stimulation-HGN)	20 (DS)	10-21 years	2 months	All 20 children were implanted with no long-term complications. We report two interval adverse events, both of which were corrected with revision surgery. Twenty participants completed the 2-month polysomnogram, with median percent reduction in titration AHI of 85% (interquartile range=75–92%). The median nightly usage for these children was 9.21 hours/night. There was a median change in the OSA-18 score of 1.15, indicating a moderate, yet significant, clinical change	HGN stimulation was safe and effective in the study population. Two minor surgical complications were corrected surgically. Overall, these data suggest that pediatric HGN stimulation appears to be a safe and effective therapy for children with DS and refractory severe OSA.
Lee et al., 2020¹⁸18 Lee NC, Hsu WC, Chang LM, Chen YC, Huang PT, Chien CC, et al. REM sleep and sleep apnea are associated with language function in Down syndrome children: An analysis of a community sample. J Formos Med Assoc. 2020 Jan;119(1 Pt 3):516-23. https://doi.org/10.1016/j.jfma.2019.07.015 https://doi.org/10.1016/j.jfma.2019.07.0...	Case series-PSG and FSIQ	30 (DS)	11.3 years	-	The presence of OSA in children with DS was 80% in the 6 to 18 age group, with 62.5% in the 6 to 12 age group; In individuals aged 6 and 12 years old, both OSA and% REM were associated with lower scores on the WPPSI-R Vocabulary test;	OSA can be highly prevalent in children with DS in the community. Among children with DS 6 and 12 years of age, OSA, and % REM were associated with their language function.
Waters et al., 2020²²22 Waters KA, Castro C, Chawla J. The spectrum of obstructive sleep apnea in infants and children with Down syndrome. Int. J. Pediatr. Otorhinolaryngol. 2020 Feb;129:109763. https://doi.org/10.1016/j.ijporl.2019.109763 https://doi.org/10.1016/j.ijporl.2019.10...	Randomized Clinical TrialPSG	152 (DS)	5.0 (1st PSG) 8.2 (2nd PSG) years	3.5 years	In a tertiary sleep unit, a full spectrum of sleep-disordered breathing in Down syndrome was seen from infancy onwards. Children having only 1 study were more likely to have a normal or mild result than those having ≥2. Studies were more often severe in children age <2 compared to those ≥2 years. After age 2 years, OSA severity increased with age. Studies evaluating the effects of surgery (most often adenotonsillectomy) showed resolution of disease to mild or normal in 53.3%.	Children having only one study were more likely to have normal results. Children with multiple studies reflected disease surveillance, including follow-up after treatment interventions.
Nerfeldt et al., 2020²¹21 Nerfeldt P, Sundelin A. Obstructive sleep apnea in children with down syndrome prevalence and evaluation of surgical treatment. Int. J. Pediatr. Otorhinolaryngol. 2020 Jun;(133):109968. https://doi.org/10.1016/j.ijporl.2020.109968 https://doi.org/10.1016/j.ijporl.2020.10...	PSG before and after OSA surgical treatment	138 (DS)	6.1 years	-	The prevalence of OSA was 82.6 and 39.9% had severe OSA (AHI: 7.6); comorbidities found were ear disease (60%), circulatory disease (51%) and endocrine disease (39%); 33 patients undergoing postoperative PSG had a residual prevalence of moderate or severe OSA of 63.6%; Pre and postoperative PSG of patients with ATE and APP presented median AHI changed from 21.1 to 12.4 and median OSA-18 from 54.0 to 35.0.	Uncertain surgical efficiency was indicated and no significant difference in results for ATE and APP was demonstrated. The authors point out that the frequency of PSG in the postoperative period was low and not systematic and that the groups were uneven and small.
Anand et al., 2021³⁰30 Anand V, Shukla G, Gupta N, Gupta A, Sapra S, Gulati S, et al. Association of sleep apnea with development and behavior in Down syndrome: a prospective clinical and polysomnographic study. Pediatr Neurol. 2021 Mar;116:7-13. https://doi.org/10.1016/j.pediatrneurol.2020.10.007 https://doi.org/10.1016/j.pediatrneurol....	PSG, Child Behavior Checklist (CBCL), developmental quotient (DQ)	53 (DS)	<18 years	-	Of 53 subjects (three to 11.8 years), 51 (96%) were found to have obstructive sleep apnea (OSA). In both three to five year and six-to-12-year age groups, there was a statistically significant positive correlation between the CBCL scores and the AHI (rho=0.77 and 0.83, respectively). There was a statistically significant negative correlation between the DQ and the AHI (rho=-0.62). In multiple linear regression, AHI was the only independent variable that was associated with CBCL and DQ.	This study provides robust evidence that OSA can negatively influence the development and behavior in children with Down syndrome as in typically developing children. Moreover, with increasing severity of OSA, children with Down syndrome have more behavioral abnormalities, especially attention deficit and hyperactivity, and also have poorer development scores.
Chamseddin et al., 2019⁴⁵45 Chamseddin BH, Johnson RF, Mitchell RB. Obstructive Sleep Apnea in Children with Down syndrome: demographic, clinical, and polysomnographic features. Otolaryngol Head Neck Surg. 2019;160(1). https://doi.org/10.1177/0194599818797308 https://doi.org/10.1177/0194599818797308...	PSG	106 (DS)	2.0-18 years	6 years	90% of children had ≥1 medical comorbidities; 95 (90%) patients had OSA; and 46 (44%) had severe OSA. Mean SaO₂ nadir was lower among obese than in nonobese children (80 vs 85%). Obese versus nonobese patients had a higher prevalence of severe OSA (56 vs 35%). The multivariable model showed that severe OSA was associated only with weight.	Obese children with DS are at a high risk for severe OSA, with weight as the sole risk factor. The results of this study show the importance of monitoring the weight of children with DS and counseling parents of children with DS about weight loss
Howard et al., 2020⁶¹61 Howard JJM, Sarber KM, Yu W, Smith DF, Tikhtman RO, Simakajornboon N, et al. Outcomes in children with down syndrome and mild obstructive sleep apnea treated non-surgically. Laryngoscope. 2020 Jul;130(7):1828-35. https://doi.org/10.1002/lary.28325 https://doi.org/10.1002/lary.28325...	PSG and oAHI	24 (DS)	<18 years	5 years	There was no significant change in oAHI, oxyhemoglobin saturation nadir, ETCO₂, or percent TST in REM after treatment for any treatment group. There was no association between reported symptoms and AHI severity or change in AHI.	In this cohort, the resolution of mild AOS was low for all treatment groups. These findings are consistent with the current understanding that OSA in children with DS is probably the result of multiple overlapping abnormalities contributing to the obstructive pathology
					OSA resolved in one patient treated with observation and two treated with medication, but worsened in two each in the medication and observation groups. Resolution of OSA occurred in 20% treated with medication, 7.7% with observation, and 0% with oxygen.	and suggests that a multimodal approach may be more appropriate in this population. Prospective studies will be useful in the future to establish a better understanding of treatment outcomes in children with DS and AOS lightweight.
Joyce et al., 2020²⁸28 Joyce A, Elphick H, Farquhar M, Gringras P, Evans H, Bucks RS, et al. Obstructive sleep apnoea contributes to executive function impairment in young children with Down syndrome. Behav Sleep Med. 2020 Sep-Oct;18(5):611-21. https://doi.org/10.1080/15402002.2019.1641501 https://doi.org/10.1080/15402002.2019.16...	Questionnaire Behavior rating inventory of executive functionpreschool version (BRIEF-P)	202 (DS)	36–71 months	-	OSA was associated with poorer working memory, emotional control and shifting.	Findings suggest that known executive function (EF) difficulties in DS are already evident at this young age. Children with DS already have limited cognitive reserve and cannot afford additional EF deficits associated with OSA. OSA is amenable to treatment and should be actively treated in these children to promote optimal cognitive development.
von Lukowicz et al., 2019⁵⁸58 von Lukowicz M, Herzog N, Ruthardt S, Quante M, Iven G, Poets CF. Effect of a 1-week intense myofunctional training on obstructive sleep apnoea in children with Down syndrome. Arch Dis Child. 2019 Mar;104(3):275-9. https://doi.org/10.1136/archdischild-2018-315064 https://doi.org/10.1136/archdischild-201...	Polygraphy	18 (DS)	6.3 years	1.5 year	Eighteen recordings had ≥3 hours of artefact free recording in both the pretreatment and posttreatment sleep study and were therefore included in the analysis. Mean age was 6.3 years; 83% had OSA prior to intervention. Mean OAHI was 6.4 before and 6.4 after the intervention; the DI3 and SpO2nadir also did not change. Only the DI90 decreased significantly from 2.7 to 2.1.	The 1-week intense myofunctional training camp evaluated here in children with DS had only a marginal effect on OSA. Whether a longer follow-up period or duration of intervention would yield stronger effects remains to be determined
Hill et al., 2018⁵⁰50 Hill CM, Elphick HE, Farquhar M, Gringras P, Pickering RM, Kingshott RN, et al. Home oximetry to screen for obstructive sleep apnoea in Down syndrome. Arch Dis Child. 2018 Oct;103(10):962-7. http://doi.org/10.1136/archdischild-2017-314409 http://doi.org/10.1136/archdischild-2017...	Case series-HPO	161 (DS)	0.5–6.0 years	-	In this training sample, the best HPO parameter predictors of OSA were the delta 12 s index >0.555 (sensitivity 92%, specificity 65%) and 3% oxyhemoglobin (SpO2) desaturation index (3% ODI)>6.15 dips/hour (sensitivity 92%, specificity 63%). Combining variables (delta 12 s index, 3% ODI, mean and minimum SpO₂) achieved a sensitivity of 96% but reduced specificity to 52%.	HPO screening could halve the number of children with DS who require multichannel sleep studies and reduce the burden on children, families, and health services alike. This approach offers a practical universal screening approach for OSA in DS that is accessible to non-specialist pediatricians.
Beppler et al., 2018⁵²52 Beppler EC, Dieffenderfer J, Songkakul T, Krystal A, Bozkurt A. An ultra-miniaturized near infrared spectroscopy system to assess sleep apnea in children with Down syndrome. Annu Int Conf IEEE Eng Med Biol Soc. 2018 Jul;2018:2877-80. http://doi.org/10.1109/EMBC.2018.8513038 http://doi.org/10.1109/EMBC.2018.8513038...	Case series-pediBand (prototype)	-	5 years	-	The potential of pediBand in measuring physiological signals that can be used in the diagnosis of OSA has been demonstrated.	It was demonstrated the potential of pediBand to successfully measure physiological signals that can be used in the diagnosis of OSA.
Best et al., 2018⁶⁰60 Best J, Mutchnick S, Ida J, Billings KR. Trends in management of obstructive sleep apnea in pediatric patients with Down syndrome. Int J Pediatr Otorhinolaryngol. 2018 Jul;110:1-5. https://doi.org/10.1016/j.ijporl.2018.04.008 https://doi.org/10.1016/j.ijporl.2018.04...	Retrospective case series	65 (DS)	4.8	8.5 years	The mean AHI was 10.7 events/hour after AT. Twenty-three patients (35.4%) underwent at least one additional surgical procedure after AT; 5 (7.7%) patients had ≥two additional procedures. The most common additional surgical procedures were revision adenoidectomies (n=8) and LT (n=13). Fifteen (23.1%) patients underwent at least one DISE to help direct selection of surgical site/s.	This retrospective case series provided the foundation for an algorithm for management of persistent OSA following primary AT in children with DS
Akkina et al., 2018⁵⁹59 Akkina SR, Ma CC, Kirkham EM, Horn DL, Chen ML, Parikh SR. Does drug induced sleep endoscopy-directed surgery improve polysomnography measures in children with Down Syndrome and obstructive sleep apnea? Acta Otolaryngol. 2018 Nov;138(11):1009-13. https://doi.org/10.1080/00016489.2018.1504169 https://doi.org/10.1080/00016489.2018.15...	PSG	24 (DS)	<18 years	3.5 years	The primary outcome was change in PSG parameters including AHI, OAHI, oxygen nadir, oxygen desaturation index, and mean carbon dioxide level. While improvement was seen in all PSG parameters, only improvement in oxygen nadir in children who had undergone prior AT was statistically significant (88.5 to 90.9%, p=04).	This study confirms a high proportion of multisite airway obstruction in DS patients with OSA. Although we observed an improvement across PSG measures, this study lacked power to detect statistically significant changes. DISE directed surgery holds promise as a beneficial tool for children with DS but a larger prospective study is needed before specific recommendations may be made on incorporating DISE into the OSA diagnostic and treatment algorithm for children with DS.
Slaats et al., 2018⁶⁵65 Slaats M, Loterman Cedric van Holsbeke C, Vos W, Van Hoorenbeeck K, et al. The role of functional respiratory imaging in treatment selection of children with obstructive sleep apnea and Down syndrome. J Clin Sleep Med. 2018 Apr;14(4):651-9. https://doi.org/10.5664/jcsm.7064 https://doi.org/10.5664/jcsm.7064...	CT before the surgical procedure and PSG in the postoperative period	33 (DS)	4.3 years	3 years	Nineteen children underwent a second PSG after AT. Seventy-nine percent had persistent OSA (OAHI> 2 events/h). A greater than 50% decrease in OAHI was observed in 79% and these children had a significantly higher volume of the regions below the tonsils.	Children with severe OSA had a reduced air passage in the upper airway. Therefore, this study suggests that an image of the upper airway may have an influence on the choice of the text. This study is a pioneer in terms of analyzing the therapeutic response with CT analysis of upper airway.
Nehme et al., 2017⁴³43 Nehme J, LaBerge R, Pothos M, Barrowman N, Hoey L, Monsour A, et al. Predicting the presence of sleep-disordered breathing in children with Down syndrome. Sleep Med. 2017 Aug;36:104-8. https://doi.org/10.1016/j.sleep.2017.03.032 https://doi.org/10.1016/j.sleep.2017.03....	Case series-PSG and sleep questionnaires	119 (DS)	6.6 years	10 years	Sleep-disordered breathing (SDB) was present in 42.9% of children, with its highest prevalence at age 8 years. Gastroesophageal reflux disease (GERD) was associated with lower odds of OAHI>5 events/hour; Presence of difficulty breathing at night, reported in the questionnaires of parents/caregivers, was significantly associated with apnea.	SDB is highly prevalent at all ages in children with Down syndrome. Symptoms did not predict SDB in this population, although GERD may mimic SDB.
Skotko et al., 2017⁵¹51 Skotko BG, Macklin EA, Muselli M, Voelz L, McDonough ME, Davidson E, et al. A predictive model for obstructive sleep apnea and Down syndrome. Am J Med Genet A. 2017 Apr;173(4):889-96. http://doi.org/10.1002/ajmg.a.38137 http://doi.org/10.1002/ajmg.a.38137...	Case series-PSG, Questionnaire, image exam	102 (DS)	3.0–24.0 years	6 months	The main outcome measure was the AHI. Using a Logic Learning Machine (with a questionnaire, imaging exam, and PSG) the best model had a cross-validated negative predictive value of 73% for mild OSA and 90% for moderate or severe OSA; positive predictive values were 55 and 25%, respectively.	In areas of the country where PSG is less available or affordable or when patients with DS are unable or unwilling to tolerate a sleep study, the model might offer, after validation, a viable alternative for providers looking to exclude moderate or severe OSA with a questionnaire.
Dudoignon et al., 2017⁵⁵55 Dudoignon B, Amaddeo A, Frapin A, Thierry B, de Sanctis L, Arroyo JO, et al. Obstructive sleep apnea in Down syndrome: Benefits of surgery and noninvasive respiratory support. Am J Med Genet A. 2017 Aug;173(8):2074-80. https://doi.org/10.1002/ajmg.a.38283 https://doi.org/10.1002/ajmg.a.38283...	Retrospective cohort	57 (DS)	5.9–6.2 years	5.5 years	33% patients required noninvasive respiratory support. Mean age at noninvasive respiratory support initiation was 7±7 years. On 11 patients with objective adherence data available, mean compliance at 2±1 years of treatment was excellent with an average use per night of 8hr46±3hr59 and 9 patient suing then on invasive respiratory support >4 hr/night. Non-invasive respiratory support was associated with an improvement of nocturnal gas exchange.	The study confirms the high prevalence and increased severity of OSA in children with DS. Upper airway surgery represents a first line treatment but has a limited efficacy. CPAP or NIV represent a very effective therapeutic option in case of persistent OSA after upper airway surgery. The major problem of CPAP/NIV is compliance but good results may be achieved by an experienced pediatric CPAP/NIV team.
Elsharkawi et al., 2017⁵³53 Elsharkawi I, Gozal D, Macklin EA, Voelz L, Weintraub G, Skotko BG. Urinary biomarkers and obstructive sleep apnea in patients with Down syndrome. Sleep Med. 2017 Jun;34:84-9. http://doi.org/10.1016/j.sleep.2017.02.005 http://doi.org/10.1016/j.sleep.2017.02.0...	Urinary biomarkers	57 (DS)	4.0–9.1 years	-	Most night-sampled urinary biomarkers were elevated among individuals with DS relative to matched HC. No urinary biomarker levels differed between individuals with DS with vs. without OSA.	DS is associated with a different urinary biomarker profile when compared to HC. While urinary biomarkers may be predictive of OSA in the general pediatric population, a different approach is needed in interpreting urinary biomarker assays in individuals with DS.
Prosser et al., 2017⁵⁷57 Prosser JD, Shott SR, Rodriguez O, Simakajornboon N, Meinzen-Derr J, Ishman SL. Polysomnographic outcomes following lingual tonsillectomy for persistent obstructive sleep apnea in down syndrome. Laryngoscope. 2017 Feb;127(2):520-4. https://doi.org/10.1002/lary.26202 https://doi.org/10.1002/lary.26202...	PSG	21 (DS)	4.3–9.3 years	10 years	The median improvement in overall AHI and the OAHI were 5.1 events/hour and 5.3 events/hour (range, 22.9 to 41), respectively. The mean oxygen saturation nadir improved from 84 to 89%. The mean time with CO₂>50 mmHg, central index, and percentage of rapid eye movement sleep were not significantly different. After surgery, the OAHI was <5 events/hour in 61.9% and ≤1 in 19% of patients.	In children with DS, persistent OSA after AT and lingual tonsil hypertrophy, LT significantly improved AHI, OAHI, and O₂ saturation nadir. We recommend that children with DS should be evaluated for lingual tonsil hypertrophy if found to have persistent OSA following T&A.
Jayaratne et al., 2017⁵⁴54 Jayaratne YSN, Elsharkawi I, Macklin EA, Voelz L, Weintraub G, Rosen D, et al. The facial morphology in Down syndrome: A 3D comparison of patients with and without obstructive sleep apnea. Am J Med Genet A. 2017 Nov;173(11):3013-21. https://doi.org/10.1002/ajmg.a.38399 https://doi.org/10.1002/ajmg.a.38399...	Stereophotography 3dMDface	63 (DS)	4.86–7.49 years	-	Participants with DS had maxillomandibular hypoplasia with smaller	Anthropometric analysis of different craniofacial landmarks
					ear, nose, and eye measurements compared to neurotypically developing peers. We found no statistically significant differences in 3D photogrammetric measurements between participants with DS with or without OSA.	and measurements demonstrated that OSA cannot be correlated with the presence, absence, or degree of any of these structural alterations within this population
Hill et al., 2016¹⁷17 Hill CM, Evans HJ, Elphick H, Farquhar M, Pickering RM, Kingshott R, et al. Prevalence and predictors of obstructive sleep apnoea in young children with Down syndrome. Sleep Med. 2016 Nov-Dec;27-28:99-106. https://doi.org/10.1016/j.sleep.2016.10.001 https://doi.org/10.1016/j.sleep.2016.10....	Case series-Polygraphy	188 (DS)	0.6–6 years	-	Moderate or severe OSA, defined by an OAHI>5/hour, was found in 14%; and mild-moderate OSA (OAHI>1<5/h) in 59% of children. Male gender and habitual snoring predicted OSA but did not have independent predictive power in the presence of the other factors. Age in months, BMI, and tonsillar size did not predict OSA.	Moderate to severe OSA is common in very young children with DS. Examination of tonsillar size did not predict OSA severity. Population-based screening for OSA is recommended in these children and domiciliary cardiorespiratory polygraphy offers an acceptable screening approach. Further research is needed to understand the natural history, associated morbidity, optimal screening methodology, and treatment modality for OSA in these children.
Maris et al., 2016⁴⁶46 Maris M, Verhulst S, Wojciechowski M, Van de Heyning P, Boudewyns A. Prevalence of obstructive sleep apnea in children with Down syndrome. Sleep. 2016 Mar;39(3):699-704. http://doi.org/10.5665/sleep.5554 http://doi.org/10.5665/sleep.5554...	Case series-PSG and questionnaire to parents/caregivers	122 (DS)	4–18 years	5 years	The overall prevalence of OSA was 66.4%.	A significant inverse correlation was found between age and AHI
Maris et al., 2016³⁷37 Maris M, Verhulst S, Saldien V, Van de Heyning P, Wojciechowski M, Boudewyns A. Drug-induced sedation endoscopy in surgically naive children with Down syndrome and obstructive sleep apnea. Sleep Med. 2016 Aug;24:63-70. https://doi.org/10.1016/j.sleep.2016.06.018 https://doi.org/10.1016/j.sleep.2016.06....	DISE e PSG	41 (DS)	4.2 years	5.5 years	Adeno-/tonsillar obstruction was found in 75.6% of the patients, and these patients subsequently underwent UA surgery; A multilevel collapse was present in 85.4%. Tongue base obstruction was present in ten patients (24.4%) and epiglottic collapse in 48.8%; A significant improvement in oAHI from 11.4/h to 5.5/h was found, but persistent OSA was present in 52% of the children.	Most patients with DS and OSA present with multilevel collapse on DISE. Adenotonsillectomy results in a significant improvement of the oAHI; however more than half of the patients had persistent OSA, probably due to multilevel collapse.
Maris et al., 2017⁴⁴44 Maris M, Verhulst S, Wojciechowski M, Van de Heyning P, Boudewyns A. Outcome of adenotonsillectomy in children with Down syndrome and obstructive sleep apnoea. Arch Dis Child. 2017 Mar;102(4). http://doi.org/10.1136/archdischild-2015-310351 http://doi.org/10.1136/archdischild-2015...	PSG	34 (DS)	2.7–5.8 years	5.5 years	The majority presented with severe OSA (58.9%). AT was performed in 22 children, tonsillectomy in 10 and adenoidectomy in two. Postoperatively, a significant improvement of the OAHI was measured from 11.4/hour to 3.6/hour, with a parallel increase of the minimum oxygen saturation. Children with initially more severe OSA had	AT results in a significant improvement of OSA in children with DS without a change in sleep efficiency or sleep stage distribution. Severe OSA was associated with a larger reduction of OSA severity.
					significantly more improvement after UA surgery. Persistent OSA was found in 47.1% of the children.
Brockmann et al.; 2016¹⁴14 Brockmann PE, Damiani F, Nuñez F, Moya A, Pincheira E, Paul MA, et al. Sleep-disordered breathing in children with Down syndrome: usefulness of home polysomnography. Int J Pediatr Otorhinolaryngol. 2016 Apr;83:47-50. https://doi.org/10.1016/j.ijporl.2016.01.030 https://doi.org/10.1016/j.ijporl.2016.01...	Case Control-HPSG	44 (DS)	3.6 years	-	83% of individuals obtained HPSG results comparable to PSG; 61% of the study subjects had OSA, 18% of which were mild to moderate cases.	A portable polysomnographic home device may be helpful for diagnosing OSA in children with DS.
Diercks et al., 2016⁶²62 Diercks GR, Keamy D, Kinane TB, Skotko B, Schwartz A, Grealish E, et al. Hypoglossal nerve stimulator implantation in an adolescent with Down syndrome and sleep apnea. Pediatrics. 2016 May;137(5):e20153663. https://doi.org/10.1542/peds.2015-3663 https://doi.org/10.1542/peds.2015-3663...	Hypoglossal nerve stimulator (HGN) Case report	1 (DS)	14 years	6 months	Hypoglossal nerve stimulator therapy was well tolerated and effective, resulting in significant improvement in the patient's OSA (overall AHI: 3.4 events/hour; AHI: 2.5–9.7 events/hour at optimal voltage settings depending on sleep stage and body position). Five months after implantation, the patient's tracheotomy was successfully removed and he continues to do well with nightly therapy.	The study demonstrated that the therapeutic measure obtained a well-tolerated and effective result, significantly reducing the patient's respiratory impairment.
Ono et al., 2015³³33 Ono J, Chishaki A, Ohkusa T, Sawatari H, Nishizaka M, Ando S. Obstructive sleep apnea-related symptoms in Japanese people with Down syndrome. Nurs Health Sci. 2015 Dec;17(4):420-5. https://doi.org/10.1111/nhs.12206 https://doi.org/10.1111/nhs.12206...	Case series-Questionnaire	90 (DS)	16.6 years	-	71% of the sample suffered from snoring, 59% had excitation, 25% apnea, and 22% nocturia; 24% had an unusual sleep posture, with the majority being from 6 to 15 years old (52%); Nocturia was the strongest predictor of unusual sleep positions for all OSA symptoms.	Symptoms related to OSA such as snoring and arousal are frequently observed in Japanese people with DS. Anatomical factors might contribute to the pathogenesis of OSA in people with DS, especially in the younger age groups. The high prevalence of unusual sleep postures may indicate a need to protect or compensate for OSA in people with DS who were less likely to be obese.
Brooks et al., 2015²⁶26 Brooks LJ, Olsen MN, Bacevice AM, Beebe A, Konstantinopoulou S, Taylor HG. Relationship between sleep, sleep apnea, and neuropsychological function in children with Down syndrome. Sleep Breath. 2015;19(1). https://doi.org/10.1007/s11325-014-0992-y https://doi.org/10.1007/s11325-014-0992-...	PSG, MSLT and neuropsychological tests	25 (DS)	7.2–18.7 years	1 year	The study demonstrated that the clinical findings were not predictive of the presence of OSA (PSG identified OSA in 10 out of 25). The author presented that there was no divergence in neuropsychological tests between children who had and did not have OSA.	Although SDB is common in children with DS, it is not a major contributor to their cognitive deficits. Cognitive function is related to the amount of sleep and particularly slow wave sleep. Successful treatment of SDB may improve their attention.
Thottam et al., 2015³⁹39 Thottam PJ, Trivedi S, Siegel B, Williams K, Mehta D. Comparative outcomes of severe obstructive sleep apnea in pediatric patients with Trisomy 21. Int J Pediatr Otorhinolaryngol. 2015 Jul;79(7):1013-6. https://doi.org/10.1016/j.ijporl.2015.04.015 https://doi.org/10.1016/j.ijporl.2015.04...	PSG in the pre and postoperative period of AT	36 (DS)	9.0 years	5.5 years	Children with DS who underwent surgery showed significant reductions in PSG obstructive and central AHI; 86.7% of children with DS presented a significant reduction in AHI for moderate or mild disease and 66.7% had resolution of central sleep apnea in the postoperative period.	Children with DS who underwent AT demonstrated significant reductions in both obstructive and central apneic indices on PSG. A significant number of patients with central sleep apnea demonstrated resolution postoperatively.
Coverstone et al.; 2014¹⁵15 Coverstone AM, Bird M, Sicard M, Tao Y, Grange DK, Cleveland C, et al. Overnight pulse oximetry for evaluation of sleep apnea among children with trisomy 21. J Clin Sleep Med. 2014 Dec;10(12):1309-15. https://doi.org/10.5664/jcsm.4286 https://doi.org/10.5664/jcsm.4286...	PSG and McGill oximetry score	119 (DS)	7.0 years	3.5 years	OAHI was ≥2.5 for 50% of all individuals; 36.1% had McGill equal to 2 and 14.3% equal to 3 or 4; McGill oximetry scores 3 and 4 are related to OSA and indicate clinical follow-up.	McGill oximetry scores of 3 or 4 reliably identified patients with marked OSDB. The possibility of central apneas causing hypoxemia must be considered in those with McGill Score 2.
Lin et al., 2014¹⁹19 Lin SC, Davey MJ, Horne RS, Nixon GM. Screening for obstructive sleep apnea in children with Down syndrome. J Pediatr. 2014 Jul;165(1):117-22. https://doi.org/10.1016/j.jpeds.2014.02.032 https://doi.org/10.1016/j.jpeds.2014.02....	Case series-PSG and McGill oximetry scale	49 (C) 49 (DS)	6.3 (C) 6.2 (DS) years	-	34.69% of children with DS presented OSA; OSA in children with DS was more severe than in children in normal development; Children with DS had a higher mean of pCO₂ during sleep and worse scores on McGill oximetry.	Children with DS have more complicated OSA and more impaired gas exchange compared to children in the control group, with similar symptoms.
Breslin et al., 2014²⁷27 Breslin J, Spanò G, Bootzin R, Anand P, Nadel L, Edgin J. Obstructive sleep apnea syndrome and cognition in Down syndrome. Dev Med Child Neurol. 2014 Jul;56(7):657-64. https://doi.org/10.1111/dmcn.12376 https://doi.org/10.1111/dmcn.12376...	Case series-PSG and cognitive assessment	38 (DS)	9.7 years	3 months	Among children with DS, mean verbal IQ score was 9 points lower in those with comorbid OSA (AHI>1.5) than in those without OSA, and performance on measures of cognitive flexibility was poorer. Children with OSA showed increased light-stage sleep at the expense of slow-wave sleep.	The results suggest that more work is needed to understand the influence of poor sleep on learning in DS and other neurodevelopmental syndromes, many of which demonstrate disordered sleep to some extent.
Stores et al., 2014⁴⁷47 Stores RJ, Stores G. The significance of aspects of screening for obstructive sleep apnoea in children with Down syndrome. J Intellect Disabil Res. 2014 Apr;58(4):381-92. http://doi.org/10.1111/jir.12033 http://doi.org/10.1111/jir.12033...	Case series-Questionnaire, Oximetry	31 (DS)	2.3–16.7 years	-	No significant association was found between objective measures of restlessness during sleep and ‘snoring’, nor were objective measures of restlessness related to reductions in overnight blood oxygen levels. –The objective measure of snoring was significantly associated with reductions in overnight blood oxygen levels.	The overnight measures used in the present study proved feasible and largely acceptable to the children and their families. More time spent familiarizing children with the procedure and the use of more recently developed recording systems would be likely to improve the success rate with this particular procedure.
Austeng et al., 2014⁴⁰40 Austeng ME, Øverland B, Kværner KJ, Andersson EM, Axelsson S, Abdelnoor M, et al. Obstructive sleep apnea in younger school children with Down syndrome. Int J Pediatr Otorhinolaryngol. 2014 Jul;78(7):1026-9. https://doi.org/10.1016/j.ijporl.2014.03.030 https://doi.org/10.1016/j.ijporl.2014.03...	Case series-PSG	29 (DS)	8.0 years	-	AHI>1.5 in 28 of 29 children and an OAI>1 in 24 of 29 children. 19 children (66%) had an AHI>5 and 17 children (59%) had an OAI>5 which indicated moderate to severe OSA. No correlation was found between OSA and obesity or gender.	The high prevalence of disease found in these previously undiagnosed 8-year-old children underlines the importance of performing OSA diagnostics in children with DS throughout childhood. These findings suggest that the prevalence of OSA remains high up to early school years.

Author/year	Study	N° of patients	Mean of age (years/months)	Time of follow up	Outcome	Conclusion
Gomes et al., 2020²⁵25 Gomes MF, Giannasi LC, Fillietaz-Bacigalupo E, de Mancilha GP, de Carvalho Silva GR, Soviero LD, et al. Evaluation of the masticatory biomechanical function in Down syndrome and its Influence on sleep disorders, body adiposity and salivary parameters. J Oral Rehabil. 2020 Aug;47(8):1007-22. https://doi.org/10.1111/joor.13023 https://doi.org/10.1111/joor.13023...	Case series-maximum mouth opening-MMO; maximum bite force-MBF; maximum voluntary clench-MVC	35 (C) 35 (DS)	19–40 years	-	Electrical activities of the masseter and temporal muscles (at rest and in maximum voluntary clench-MVC), maximum bite force-MBF, and maximum mouth opening-MMO were investigated.	Masseter and temporal muscle hypotonia were found in all atypical subjects with DS. This muscle dysfunction strongly was related to overweight/obesity, risks for development of cardiovascular/metabolic diseases, OSA severity, successive snoring episodes, and salivary flow reduction in DS.

Author/Year	Study	N° of patients	Mean age (years/months)	Time of follow up	Outcome	Conclusion
Chawla et al., 2021²⁴24 Chawla JK, Howard A, Burgess S, Heussler H. Sleep problems in Australian children with Down syndrome: the need for greater awareness. Sleep Med. 2021 Feb;78:81-7. https://doi.org/10.1016/j.sleep.2020.12.022 https://doi.org/10.1016/j.sleep.2020.12....	Case series-CSHQ and sleep clinic	76 (DS)	-	-	The first study to report the prevalence of sleep problems in Australian children with DS and to compare a community and referred group of children with DS directly.	This study reports a high prevalence of sleep problems in both a community and referred group of Australian children with DS, and suggests that there are many children with DS and sleep problems, particularly non-respiratory difficulties, who are potentially not receiving adequate treatment.
Santoro et al., 2021³⁴34 Santoro JD, Del Rosario J, Osterbauer B, Gillett ES, Don DM. Sleep positions in children with Down syndrome and obstructive sleep apnea. Sleep Med. 2021 May;81:463-5. https://doi.org/10.1016/j.sleep.2021.03.018 https://doi.org/10.1016/j.sleep.2021.03....	PSG	82 (DS)	<18 years	-	Reported sleep positions were skewed towards lateral/decubitus (82.9%) compared to prone (11.0%) and supine (6.1%). This was consistent with hypnogram data where 71% of total sleep time in lateral/decubitus positions compared to prone (13%) and supine (6%). Tonsillectomy was associated with lower obstructive AHI (OAHI) Sleep position was not associated with age, gender, race, ethnicity, nor history of tonsillectomy. Preferred sleep position was not correlated with OAHI or OSA severity.	This study highlights the possibility that children with DS may have preferential sleep positions that cater to optimized airflow in the context of OSA, although further prospective study is needed.
Shaw et al., 2021²⁹29 Shaw D, Bar S, Champion JD. The Impact of developmental behavioral pediatrics in a population of children with Down syndrome. J Pediatr Nurs. 2021 Mar-Apr;57:38-42. https://doi.org/10.1016/j.pedn.2020.10.019 https://doi.org/10.1016/j.pedn.2020.10.0...	DSM 5 criteria and individual medical record numbers (MRN's) Chi-square test and Fisher's exact AND Student's t-test	370 (DS)	2–17 years	1.5 year	Compared to typically developing children, children with DS may have more challenges with adaptive functioning in the school setting (examples include complying with directions and task persistence). Parents and teachers report higher rates of	Developmental/behavioral assessment is integral for detection of co-morbid conditions among a pediatric DS population and prevention of diagnostic overshadowing.
					non-compliance in children with DS compared to those without DS secondary to their executive functioning and adaptive deficits
Bassam et al., 2021³¹31 Bassam A, Thacker J, Walter LM, Davey MJ, Nixon GM, Horne RS. Nocturnal dipping of heart rate is impaired in children with Down syndrome and sleep disordered breathing. Sleep Med. 2021 May;81:466-73. https://doi.org/10.1016/j.sleep.2021.03.020 https://doi.org/10.1016/j.sleep.2021.03....	Heart rate (HR) and pulse transit time (PTT) (a surrogate inverse measure of BP change)	19 (DS) 19 (C)	3–18 years	-	Children with DS exhibited reduced nocturnal dipping of HR during total sleep. Fewer children with DS exhibited a greater than 10% fall in HR between wake and REM sleep compared to TD+children.	Findings demonstrate significantly reduced nocturnal dipping of HR in children with DS compared to TD children matched for SDB severity, suggesting SDB has a greater cardiovascular effect in these children. Further studies are required to fully understand the mechanisms involved and to assess if treatment of SDB improves nocturnal dipping.
Siriwardhana et al., 2021³²32 Siriwardhana LS, Nixon GM, Davey MJ, Mann DL, Landry SA, Edwards BA, et al. Children with down syndrome and sleep disordered breathing display impairments in ventilatory control. Sleep Med. 2021 Jan;77:161-9. https://doi.org/10.1016/j.sleep.2020.12.005 https://doi.org/10.1016/j.sleep.2020.12....	PSG, nasal pressure, and transcutaneous carbon dioxide (TcCO₂)	14 (DS) 14 (C)	3–19 years	2.5 years	Children with Down syndrome also had significantly lower average oxygen saturation associated within each analysis window compared to typically developing children	Higher loop gain in children with Down syndrome and sleep disordered breathing indicates that these children have more unstable ventilatory control, compared to age, gender and sleep disordered breathing severity matched typically developing children. This may be due to an inherent impairment in ventilatory control in children with Down syndrome contributing to their increased risk of sleep disordered breathing, which may inform alternative treatment options for this population.
Richard et al., 2020⁴²42 Richard N, Beydon N, Berdah L, Corvol H, Aubertin G, Taytard J. Nocturnal hypoventilation in Down syndrome children with or without sleep apnea. Pediatr Pulmonol. 2020 May;55(5):1246-53. https://doi.org/10.1002/ppul.24703 https://doi.org/10.1002/ppul.24703...	Case series-PSG and clinical files	28 (DS) 28 (C)	<18 years	5 years	Mean transcutaneous partial pressure of carbon dioxide (PtcCO2) during sleep was significantly higher in patients with DS compared to controls.	This was the first study to compare nocturnal gas exchange in children with DS to a control group of children with similar OSA, but not DS. Data demonstrated that children with DS have increased transcutaneous partial pressure of carbon dioxide (PtcCO₂) regardless of the presence of OSA and its severity. This may be due to respiratory muscle hypotonia and/or ventilatory control alteration in patients with DS.
Giménez et al., 2018¹⁶16 Giménez S, Videla L, Romero S, Benejam B, Clos S, Fernández S, et al. Prevalence of sleep disorders in adults with down syndrome: a comparative study of self-reported, actigraphic, and polysomnographic findings. J Clin Sleep Med. 2018 Oct;14(10):1725-33. https://doi.org/10.5664/jcsm.7382 https://doi.org/10.5664/jcsm.7382...	Case series-PSG, self-reports and, actigraphy.	35 (C) 47 (DS)	39.2 (C) 39.6(DS) years	-	Adults with DS had lower sleep efficiency, lower %REM, higher prevalence of OSA (78 versus 14%) and a higher AHI than patients in the control group. The DS group questionnaires (PSQI and ESS) did not reflect the sleep disorders detected in the PSG.	Adults with DS have more sleep disorders, especially OSA. Sleep disorders were not detected by self-reported sleep measures. Actigraphy, PSG and simplified devices validated for OSA screening are important tools for diagnosis.
Maris et al., 2016²⁰20 Maris M, Verhulst S, Wojciechowski M, Van de Heyning P, Boudewyns A. Sleep problems and obstructive sleep apnea in children with down syndrome, an overview. Int J Pediatr Otorhinolaryngol. 2016 Mar;82:12-5. https://doi.org/10.1016/j.ijporl.2015.12.014 https://doi.org/10.1016/j.ijporl.2015.12...	Case series-CSHQ and PSG	54 (DS)	8.9 (C) 7.5 (DS) years	-	According to the CSHQ, 74.1% of children with DS had sleep problems.	Children with DS have a significantly higher prevalence of sleep problems, compared to.
					The general sleep problems were not related to age or gender, however, boys suffer more from daytime sleepiness. Symptoms of respiratory sleep disorders are related to parasomnias, longer sleep duration, and more daytime sleepiness.	normal developing healthy school-aged children. No correlations were found between the relative reports on sleep problems and the underlying OSA or severity of OSA.
Ong et al., 2018⁵⁶56 Ong AA, Atwood CM, Nguyen SA, Teufel RJ, Lal C, LaRosa AC, et al. Down syndrome and pediatric obstructive sleep apnea surgery: A national cohort. Laryngoscope. 2018 Aug;128(8):1963-9. https://doi.org/10.1002/lary.27063 https://doi.org/10.1002/lary.27063...	Case series-Retrospective cohort database analysis	51292 (DS)	0–20	15 years	Tonsillectomy with adenoidectomy was the most common procedure in both groups, but the proportion of tonsillectomy with adenoidectomy decreased over time. –The proportion of palatal surgery and tracheostomy also decreased significantly, whereas there was an increase in the proportion of lingual tonsillectomies, tongue-base reduction procedures, and supraglossoplasty performed in both groups over time. The relative rates of change in these procedures were higher in the DS population.	Tonsillectomy with adenoidectomy remains the most commonly performed procedure, although there was a significant increase in other sleep surgeries performed (LT, tongue-base reduction, and supraglossoplasty) between the two study periods, especially in children with DS.
Mylavarapu et al., 2016⁶⁴64 Mylavarapu G, Subramaniam D, Jonnagiri R, Gutmark EJ, Fleck RJ, Amin RS, et al. Computational modeling of airway obstruction in sleep apnea in down syndrome: a feasibility study. Otolaryngol Head Neck Surg. 2016 Jul;155(1):184-7. https://doi.org/10.1177/0194599816639544 https://doi.org/10.1177/0194599816639544...	Computational fluid dynamics, virtual surgery, CT and MRI	10 (DS)	5 years	-	There was a reduction, in 8 out of 10 patients, of AHI and the resistance of upper airway, when compared to baseline values.	This study highlights the need for future studies, before using this technique in surgical plans.
Hoffmire et al., 2014²³23 Hoffmire CA, Magyar CI, Connolly HV, Fernandez ID, van Wijngaarden E. High prevalence of sleep disorders and associated comorbidities in a community sample of children with Down syndrome. J Clin Sleep Med. 2014 Apr;10(4):411-9. https://doi.org/10.5664/jcsm.3618 https://doi.org/10.5664/jcsm.3618...	Case series-CSHQ and PSQ	107 (DS)	7–17 years	2 years	65% of children with DS had sleep problems in the CSHQ, but these problems were not reported by their parents; In PSQ, 46% of children had sleep-related breathing problems and 21% sleep-related movement disorders; Children with asthma, autism and a history of enlarged adenoids and tonsils had more frequent sleep problems than children without these comorbidities.	Sleep disorders are important but also under-recognized problems in children with DS. It appears to be correlated with some prevalent comorbidities, which may provide guidance to augment current practice guidelines to evaluate sleep problems in this population.
Nisbet et al., 2014³⁶36 Nisbet LC, Phillips NN, Hoban TF, O’Brien LM. Effect of body position and sleep state on obstructive sleep apnea severity in children with Down syndrome. J Clin Sleep Med. 2014 Jan;10(1):81-8. https://doi.org/10.5664/jcsm.3368 https://doi.org/10.5664/jcsm.3368...	Case series-PSG and body posture record during sleep	76 (C) 76 (DS)	5.1 (C) 4.6 (DS) years	4.5 years	Sensor-recorded position (supine, prone, lateral) was expressed as the percentage of total sleep time. The apnea-hypopnea index (AHI) was calculated in each sleep state (NREM, REM), position, and position-sleep state combination. AHI was higher in REM than NREM; nonetheless, the NREM AHI was higher in DS than NREM AHI that controls.	In DS and non-DS children alike, respiratory events are predominantly REM-related. However, when matched for OSA severity, children with DS have a higher NREM AHI, which is worse in the supine position, perhaps indicating a positional effect compounded by underlying hypotonia inherent to DS.
					The percentage of prone sleep was greater in DS than controls, but of supine or non-supine sleep was not different between them.
Konstantinopoulou et al., 2016⁴¹41 Konstantinopoulou S, Tapia IE, Kim JY, Xanthopoulos MS, Radcliffe J, Cohen MS, et al. Relationship between obstructive sleep apnea cardiac complications and sleepiness in children with Down syndrome. Sleep Med. 2016 Jan;17:18-24. https://doi.org/10.1016/j.sleep.2015.09.014 https://doi.org/10.1016/j.sleep.2015.09....	Case series-PSG, ECG and BPN	23 (DS)	2.7 months	-	At four months, there were no changes in cardiovascular outcomes or sleepiness between those on actual versus sham CPAP. Hours of actual CPAP use were associated with improved left ventricle function.	In children with DS, left ventricle diastolic function correlated with OSA severity, which improved with the use of CPAP. There was a tendency towards increased sleepiness in those with OSA, which correlated with the rate of awakening.
Senthilvel and Krishna, 2011³⁵35 Senthilvel E, Krishna J. Body position and obstructive sleep apnea in children with Down syndrome. J Clin Sleep Med. 2011 Apr;7(2):158-62.	PSG	17 (C) 17 (DS)	6 years	1.5 year	History of previous tonsillectomy (41%), congenital heart disease (of any type) (82%) and hypothyroidism (41%) of SD compared to 24%, 12 and 0%, respectively of C. SD assumed a unique body position sitting cross-legged flopped-forward with head resting on bed while asleep.	Some DS children assume a peculiar body position, sitting cross-legged flopped-forward with head resting on bed while asleep. This is absent in age and gender-matched controls showing otherwise similar PSG characteristics. The reason for this posture is unclear from this study.

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[1] Correspondence: Fernando Morgadinho Santos Coelho; Email: fernandomorgadinho@hotmail.com.