| Talli et al. (2016)30
|
Greece |
To investigate whether specific language disorders and dyslexia are different disorders or whether reading deficiencies are always present in DLD. |
Cross-sectional study. The sample comprised 15 preschoolers with language disorders diagnosed with DLD by speech-language-hearing therapists, and 15 children diagnosed with dyslexia in 2nd and 3rd grades with an interdisciplinary assessment in Greek hospitals. The control group had 30 children in elementary school. Decoding, phonological awareness, and reading comprehension skills were assessed. |
This study did not consider DLD and dyslexia as comorbid disorders, as the group comparison revealed more evidence of phonological skill deficits in the DLD group than in the dyslexia group. The reading comprehension performance of 8 out of the 30 children in the two clinical groups was within normative standards (3 in the DLD group and 5 in the dyslexia group).
80% of children with DLD had phonological deficits, in contrast with only 47% in the dyslexia group. |
| Ramus et al. (2013)21
|
England |
To compare children with DLD and dyslexia, with DLD alone, and with dyslexia alone to verify their phonological and cognitive skills. |
Cross-sectional study. The sample initially comprised 129 children: 30 with DLD and dyslexia, 13 with DLD alone, 21 with dyslexia alone, and 65 children in the control group. The following skills were assessed: phonological awareness, morphosyntax, prosody, nonword reading, vocabulary, phonological working memory, and reading comprehension. |
The language skills assessed in the study revealed that children with DLD do not always have phonological deficits and reading impairments. While DLD and dyslexia may often coexist, there is DLD alone and dyslexia alone.
Children with dyslexia alone are characterized by phonological skill impairments, just below average in vocabulary, not in grammar skills. Children with comorbid DLD and dyslexia were characterized by deficits in the three language dimensions studied, and these deficits were generally more severe than in children with DLD or dyslexia alone. Children with DLD alone are similarly impaired in expression and phonological skills. |
| Lauterbach et al. (2017)28
|
United States of America |
To explore the performance of cognitive and language variables in predicting reading skills in children with dyslexia and DLD and analyze which variables are more predictive to distinguish the two groups. |
Cross-sectional study. The sample comprised 44 participants with dyslexia and 19 with DLD. The following skills were assessed: phonological awareness, nonword reading, reading comprehension, cognitive variables, and working memory. |
The group of participants with dyslexia performed better in overall intellectual skills, reading, and verbal and oral comprehension. However, they had lower scores in phonemic awareness skills than the DLD group. Working memory was the main predictor of pseudoword reading in the DLD group; in the dyslexia group, it was phonological awareness. It was observed that verbal comprehension, phonological awareness, and reading decoding efficiency can be used to distinguish both groups. |
| McCarthy (2014)23
|
United States of America |
To investigate how oral language and word reading relate to spelling skills in children with DLD, dyslexia, and both, in comparison with peers with typical development. |
Case-control. The sample comprised 43 children with DLD, 21 with dyslexia, and 18 with both. Word reading and spelling performance were assessed. |
Children with dyslexia and DLD/dyslexia had low spelling precision, and additional support to the theory that dyslexia and DLD are comorbid, characterized by phonological, spelling, and semantic errors. |
| Farquharson et al.(2014)29
|
United States of America |
To examine the influence of phonological and lexical characteristics on phonological awareness in children with dyslexia and/or DLD. |
Cross-sectional study. The sample comprised 33 children with typical development, 13 with DLD, and 18 with dyslexia, studying in 2nd grade. Phonological awareness and word decoding skills were assessed. Each child completed a battery of assessments encompassing language, word decoding, nonverbal intelligence, and phonological awareness. Measures included both standardized assessments and experimental tasks. |
Children with dyslexia had greater difficulties characterized by phonological deficits than their peers with DLD and typical development. |
| Spanoudis et al.(2019)24
|
Cyprus |
To investigate the possible co-occurrence of DLD and dyslexia and the nature of such a co-occurrence in linguistical and cognitive terms in an orthographically consistent language. |
Cross-sectional study. The sample comprised 140 2nd- and 4th-grade Greek Cypriot children, divided into 4 groups: comorbid group, dyslexia group, DLD group, and control group with no deficits. The following skills were assessed: reading, grammar, receptive vocabulary, mental lexicon access, phonological working memory, semantics, and spelling. |
In cognitive measures, the DLD group had a worse result in memory figures, digits, phonological memory, and naming speed. In language, they had comparable deficits in semantics and reading comprehension, without related impairments in phonological awareness.
Children with DLD and dyslexia have characteristics in common, with impaired semantics, reading comprehension, short-term verbal memory, and word spelling identification. However, they manifest different symptoms. The control group performed significantly better, with fewer cognitive and language impairments. |
| Snowling et al. (2019)25
|
England |
To screen the progress reading problems from initial developmental stages. |
Longitudinal study. The sample comprised 260 children, divided into children with risk factors for language changes, at family risk, and with typical development. The following skills were assessed: reading, receptive and expressive grammar, rapid automatic naming, phonological awareness, vocabulary, comprehension, and executive functions. |
Phonological deficits are risk factors present in both dyslexia and DLD. Those with comorbid DLD and dyslexia have more severe impairments in reading and phonological awareness than children with either disorder alone. |
| Schuchardt et al.(2013)27
|
Germany |
To investigate whether children with learning disorders have working memory deficits like children with DLD. |
Cross-sectional study. The sample comprised 113 children divided into 5 groups: 30 children with dyslexia; 16 with dyslexia that receive special education; 19 with combined school skill difficulties; 18 with combined school skill difficulties that receive special education; and 30 in a control group. Working memory, executive functions, and visuospatial skills were assessed. |
Deficits were found in the phonological loop and executive functions in children with dyslexia and with DLD. Phonological functioning deficits were broader and deeper in children with DLD. |
| Wong et al. (2017)26
|
China |
To examine whether working memory and superior language skills were responsible for individual differences between Chinese children in reading comprehension and whether children with DLD or dyslexia had deficits in these skills. |
Cross-sectional study. The sample comprised 82 Cantonese-speaking Chinese children aged 7 and 8 years, with typical development, dyslexia, DLD, and both. Working memory and reading comprehension skills were assessed. |
Children with DLD alone and dyslexia alone had different deficit profiles. The comorbid DLD-D group was worse in reading comprehension than the DLD alone group, but not the D alone group. The comorbid DLD-D group did not perform worse than either group with a disorder alone in superior language skills associated with reading comprehension. |
| Adlof et al.(2021)31
|
United States of America |
To examine group differences in word learning overall measures in children with DLD alone and dyslexia alone, comparing with one another, with peers with both DLD and dyslexia, and with peers with typical development. |
Cross-sectional study. The sample comprised children (N = 244) aged 7 years and 10 months to 9 years and 4 months. Language, reading fluency, phonological memory, nonverbal cognitive, and semantic skills (naming and recalling) were assessed. |
Children with dyslexia alone performed significantly better in existing vocabulary measures than their peers with DLD alone. In experimental word learning measures, children in dyslexia alone and DLD+dyslexia groups performed significantly worse than children with typical development in all word learning tasks. Children with DLD alone significantly differed from the typical development group in a single word learning task assessing verbal semantic recalling. |
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