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Clinical and molecular characterization of a Brazilian cohort of campomelic dysplasia patients, and identification of seven new SOX9 mutations

Abstract

Campomelic dysplasia (CD) is an autosomal, dominantly inherited, skeletal abnormality belonging to the subgroup of bent bone dysplasias. In addition to bowed lower limbs, CD typically includes the following: disproportionate short stature, flat face, micrognathia, cleft palate, bell-shaped thorax, and club feet. Up to three quarters of 46, XY individuals may be sex-reversed. Radiological signs include scapular and pubic hypoplasia, narrow iliac wings, spaced ischia, and bowed femora and tibiae. Lethal CD is usually due to heterozygous mutations in SOX9, a major regulator of chondrocytic development. We present a detailed clinical and molecular characterization of nine Brazilian CD patients. Infants were either stillborn (n = 2) or died shortly after birth and presented similar phenotypes. Sex-reversal was observed in one of three chromosomally male patients. Sequencing of SOX9 revealed new heterozygous mutations in seven individuals. Six patients had mutations that resulted in premature transcriptional termination, while one infant had a single-nucleotide substitution at the conserved splice-site acceptor of intron 1. No clear genotype-phenotype correlations were observed. This study highlights the diversity of SOX9 mutations leading to lethal CD, and expands the group of known genetic alterations associated with this skeletal dysplasia.

campomelic dysplasia; skeletal dysplasia; osteochondrodysplasias; SOX9; prenatal diagnosis


Introduction

Campomelic dysplasia (CD) is an autosomal dominant condition classified among the bent bone skeletal dysplasias (Warman et al., 2011Warman ML, Cormier-Daire V, Hall C, Krakow D, Lachman R, LeMerrer M, Mortier G, Mundlos S, Nishimura G, Rimoin DL et al. (2011) Nosology and classification of genetic skeletal disorders: 2010 revision. Am J Med Genet A 155A:943–968.). Typical manifestations of CD include shortening and bowing of the long bones, hypoplasia of the scapula, absence of ossification of the dorsal vertebral pedicles, and an abnormal pelvic bone pattern, with narrow iliac wings, spaced ischia, and hypoplastic/absent pubis bones. These findings warrant the diagnosis of CD in both prenatal ultrasonographic evaluation and postnatal radiological examination.

Clinically, CD is characterized by disproportionally short stature, short and bowed limbs, pretibial skin dimples, club feet, hip dislocation, thoracic constriction, cleft palate, micro- and/or retrognathia, and midface hypoplasia (Maroteaux et al., 1971Maroteaux P, Spranger J, Opitz JM, Kucera J, Lowry RB, Schimke RN, Kagan SM (1971) The campomelic syndrome. Presse Med 79:1157–1162.; Spranger et al., 2002Spranger JW, Brill PW, Poznanski A (2002) Bone Dysplasias -An Atlas of Genetic Disorders of Skeletal Development. 2nd edition. Oxford University Press, New York, 613 pp.). Additionally, up to three quarters of karyotypically male (46,XY) patients are sex-reversed, with phenotypically normal external female genitalia (Massardier et al., 2008Massardier J, Roth P, Michel-Calemard L, Rudigoz RC, Bouvier R, Dijoud F, Arnould P, Combourieu D and Gaucherand P (2008) Campomelic dysplasia: Echographic suspicion in the first trimester of pregnancy and final diagnosis of two cases. Fetal Diagn Ther 24:452–457.). Most infants with typical CD die shortly after birth due to pulmonary hypoplasia. However, patients diagnosed with a CD variant known as acampomelic campomelic dysplasia (ACD) usually survive the neonatal period and may reach adult life without major disabilities, but give birth to affected children (Gordon et al., 2009Gordon CT, Tan TY, Benko S, Fitzpatrick D, Lyonnet S and Farlie PG (2009) Long-range regulation at the SOX9 locus in development and disease. J Med Genet 46:649–656.; Lecointre et al., 2009Lecointre C, Pichon O, Hamel A, Heloury Y, Michel-Calemard L, Morel Y, David A and Le Caignec C (2009) Familial acampomelic form of campomelic dysplasia caused by a 960 kb deletion upstream of SOX9. Am J Med Genet A 149A:1183–1189.).

CD has been the subject of intense investigation for over twenty years, since its original genetic linkage to human chromosome 17 (Tommerup et al., 1993Tommerup N, Schempp W, Meinecke P, Pedersen S, Bolund L, Brandt C, Goodpasture C, Guldberg P, Held KR and Reinwein H (1993) Assignment of an autosomal sex reversal locus (SRA1) and campomelic dysplasia (CMPD1) to 17q24.3-q25.1. Nat Genet 4:170–174.) and the subsequent characterization of SOX9 as the locus involved (Foster et al., 1994Foster JW, Dominguez-Steglich MA, Guioli S, Kwok C, Weller PA, Stevanovic M, Weissenbach J, Mansour S, Young ID and Goodfellow PN (1994) Campomelic dysplasia and autosomal sex reversal caused by mutations in an SRY-related gene. Nature 372:525–530.; Wagner et al., 1994Wagner T, Wirth J, Meyer J, Zabel B, Held M, Zimmer J, Pasantes J, Bricarelli FD, Keutel J, Hustert E et al. (1994) Autosomal sex reversal and campomelic dysplasia are caused by mutations in and around the SRY-related gene SOX9. Cell 79:1111–1120.). The vast majority of CD cases (as well as some ACD cases) are attributed to haploinsufficiency, due to de novo mutations in the coding region of SOX9, a master regulator of chondrogenesis and SRY-mediated testicular development (Foster et al., 1994Foster JW, Dominguez-Steglich MA, Guioli S, Kwok C, Weller PA, Stevanovic M, Weissenbach J, Mansour S, Young ID and Goodfellow PN (1994) Campomelic dysplasia and autosomal sex reversal caused by mutations in an SRY-related gene. Nature 372:525–530.; Wagner et al., 1994Wagner T, Wirth J, Meyer J, Zabel B, Held M, Zimmer J, Pasantes J, Bricarelli FD, Keutel J, Hustert E et al. (1994) Autosomal sex reversal and campomelic dysplasia are caused by mutations in and around the SRY-related gene SOX9. Cell 79:1111–1120.; Gordon et al., 2009Gordon CT, Tan TY, Benko S, Fitzpatrick D, Lyonnet S and Farlie PG (2009) Long-range regulation at the SOX9 locus in development and disease. J Med Genet 46:649–656.). Conversely, a greater proportion of ACD patients is characterized by genomic imbalances in the vicinity of SOX9, a gene desert region that encompasses approximately 2 Mb in chromo-some 19q24.3-25 (Gordon et al., 2009Gordon CT, Tan TY, Benko S, Fitzpatrick D, Lyonnet S and Farlie PG (2009) Long-range regulation at the SOX9 locus in development and disease. J Med Genet 46:649–656.).

In this paper, we present nine Brazilian CD patients who were diagnosed either prenatally or shortly after birth. Major clinical and radiologic findings are detailed for all cases. Sequencing of SOX9 revealed mutations in seven of them, all of which had not been previously described. This work is a report on one of the largest cohorts of CD patients, and it highlights the mutational diversity of SOX9 mutations.

Material, Subjects and Methods

From April 2012 to November 2013, clinical data from patients suspected of having CD were either retrospectively (for patient 1 and patients 3 to 7) or prospectively (patients 2, 8, and 9) referred to our Institution from different Brazilian medical genetics services, and here they were evaluated by two clinical geneticists (MTVS or DPC). Photographs, radiographs, and medical records were used to characterize the findings of each patient, both clinically and radiologically. Standard growth curves were utilized to determine percentiles for birth length (BL), birth weight (BW), and occipitofrontal circumference (OFC).

DNA was extracted from peripheral blood and used to amplify all exons and exon-intron boundaries of SOX9 by polymerase chain reaction (PCR), in nine patients. For patient 9 only, DNA from both parents was also obtained. Amplification products were purified by treatment with an exonuclease I / shrimp alkaline phosphatase protocol and subjected to conventional Sanger sequencing using an ABI 3130xl Genetic Analyzer (Applied Biosystems). CodonCode Aligner software, version 4.2.1 demo (CodonCode Corporation), was used to align sequences and analyze electropherograms. SOX9 reference sequences ENSG00000125398.5 (genomic) and ENSP00000245479.2 (protein) from ENSEMBL were used as wild type references. Nucleotide numbering of mutations followed the base positions of SOX9 cDNA reference sequence CCDS_11689.1 from NCBI.

When the karyotype was not available, the genotypic sex of patients was inferred from the amplification of X and Y chromosome-specific sequences in zinc finger protein, X-linked (ZFX), and sex determining region Y (SRY) genes, respectively. Primer sequences and PCR conditions are available upon request. The Spliceman web server (Lim and Fairbrother, 2012Lim KH and Fairbrother WG (2012) Spliceman - A computational web server that predicts sequence variations in pre-mRNA splicing. Bioinformatics 28:1031–1032.) was used to estimate the pathogenicity of the splice-site mutation identified in patient 3.

Ethical approval for this study was obtained from both the Institutional Review Board of the Hospital de Clínicas de Porto Alegre, and the Brazilian National Committee for Ethics in Research (project number 07044212.3.0000.5327).

Results

The main clinical data from the nine CD patients are summarized in Table 1. Examples of typical clinical and radiological findings are also illustrated in Figure 1. All infants displayed the typical CD phenotype, and they were either stillborn or died shortly after birth. Sex reversal was found in one of the 46,XY patients (patient 7). The mean gestational age (GA) at birth, considering live births only, was 36.4 ± 2.5 weeks. BW was within the normal range in the majority of patients (mean = 2,672.8 ± 699.0 g), while BL was below the 10th percentile in all patients whose measurement data were available (mean = 40.7 ± 3.1 cm). Most infants had macrocephaly, with OFCs above the 90th percentile for the GA (mean = 36.1 ± 1.8 cm). No live born infants survived the neonatal period. Shortened and bowed limbs were found in all patients — additional dysmorphic features are detailed in Table S1 Table S1 Detailed clinical evaluation of CD patients included in the study. . Of note, craniofacial anomalies (micro/retrognathia, flat face, flat nasal bridge) were highly prevalent in this cohort. Post-natal radiographies were obtained for all patients — a detailed assessment of skeletal abnormalities is presented in Table S2 Table S2 Detailed radiological evaluation of CD patients included in the study. . Bowing of the femora and tibia and malformation of the pelvic bones were consistently found.

Table 1
Clinical characteristics of the investigated CD patients.
Figure 1
Typical campomelic dysplasia findings observed in the patients included in this study. A: Antero-posterior (AP) radiography of patient 7, showing short long bones with bowed femora and tibiae, a short thorax with eleven pairs of ribs, and hypoplastic pubic bones, although no SOX9 mutation was identified. B: Lateral radiography of patient 2. Bowing of the femora and tibiae, as well as thoracic constriction, are identifiable. C: AP radiography of patient 9. In addition to the skeletal abnormalities already described in patients 1 and 2, hypoplastic scapulae are present. D: Clinical picture of patient 2 at necropsy. A small, flat face can be observed, as well as micro- and retrognathia, and cleft palate. E: Clinical picture of patient 1 at necropsy, illustrating the club feet and the pre- and post-tibial skin dimples characteristic of CD.

DNA was available for molecular analysis for all patients, and putative pathogenic heterozygous SOX9 mutations were found in seven individuals, which equates to a mutational detection rate of 78% (see Table 1). Mutations shown in Figure 2 for patients 1, 2, 5, 6, 8, and 9 predicted the insertion of a premature termination codon, either due to a stop codon mutation (patients 2, 5, and 6), or a frame shift mutation (patients 1, 8, and 9).

Figure 2
SOX9 mutations identified in six CD patients included in the study. For each image, a fragment of the wild type (wt) allele with the corresponding codified amino acids is shown (except for C, where the junction between the first exon and intron is depicted). Altered nucleotides in the mutant (mt) allele are depicted in red. A: frame shift mutation of patient 1 due to a 1-bp deletion. B-E: Single-nucleotide change observed in patients 2, 3, 5, and 6,respectively. F: frame shift mutation in patient 8 due to a 1-bp deletion. G: frame shift mutation in patient 9 due to a 7-bp deletion.

An A-to-G substitution was identified in the conserved 3′ splice-site of intron 1 of patient 3. In silico analysis using the Spliceman web server, which ranks putative donor and acceptor splice-site mutations based on exon/intron sequence conservation among different species, predicted a pathogenic consequence for this mutation, with a probability of 67%. Representative sequencing results are shown in ± for each patient with an identified mutation. Because of the absence of DNA from parents in most cases, molecular confirmation of a de novo mutation was only possible for patient 9, although parents of all patients were phenotypically normal.

Discussion

In this study, we sought to characterize a large cohort of CD patients in Brazil at the clinical, radiological and molecular levels. Our study recapitulated several observations previously reported, and this illustrated a striking degree of homogeneity among CD patients, considering clinical and radiological findings. We were able to identify different heterozygous mutations in the coding region of SOX9, in seven of the nine patients. However, not unlike others (Wagner et al., 1994Wagner T, Wirth J, Meyer J, Zabel B, Held M, Zimmer J, Pasantes J, Bricarelli FD, Keutel J, Hustert E et al. (1994) Autosomal sex reversal and campomelic dysplasia are caused by mutations in and around the SRY-related gene SOX9. Cell 79:1111–1120.; Kwok et al., 1995Kwok C, Weller PA, Guioli S, Foster JW, Mansour S, Zuffardi O, Punnett HH, Dominguez-Steglich MA, Brook JD and Young ID (1995) Mutations in SOX9, the gene responsible for campomelic dysplasia and autosomal sex reversal. Am J Hum Genet 57:1028–1036.; Meyer et al., 1997Meyer J, Südbeck P, Held M, Wagner T, Schmitz ML, Bricarelli FD, Eggermont E, Friedrich U, Haas OA, Kobelt A et al. (1997) Mutational analysis of the SOX9 gene in campomelic dysplasia and autosomal sex reversal: Lack of genotype/phenotype correlations. Hum Mol Genet 6:91–98.), a subset of the screened patients (2 out of 9) did not have any nucleotide variation in the coding region of SOX9. Of course, a heterozygous deletion within SOX9 or imbalances of regulatory elements in its genomic vicinity cannot be ruled out. These hypotheses shall be further investigated for patients 4 and 7.

Although SOX9 is a small gene, spanning little more than 5 kb and three exons, a plethora of studies have characterized regulatory DNA elements located both upstream and downstream from the gene that regulates SOX9 expression, both temporally and tissue-specifically (Bagheri-Fam et al., 2006Bagheri-Fam S, Barrionuevo F, Dohrmann U, Günther T, Schüle R, Kemler R, Mallo M, Kanzler B and Scherer G (2006) Long-range upstream and downstream enhancers control distinct subsets of the complex spatiotemporal Sox9 expression pattern. Dev Biol 291:382–397.). For instance, cumulative evidence has suggested that a 78 kb genomic region upstream from SOX9 plays a role in testicular expression, given that deletion of this putative regulatory element has been observed in some 46,XY sex-reversed individuals (Pop et al., 2004Pop R, Conz C, Lindenberg KS, Blesson S, Schmalenberger B, Briault S, Pfeifer D and Scherer G (2004) Screening of the 1 Mb SOX9 5′ control region by array CGH identifies a large deletion in a case of campomelic dysplasia with XY sex reversal. J Med Genet 41:e47.). Likewise, isolated Pierre-Robin (Fukami et al., 2012Fukami M, Tsuchiya T, Takada S, Kanbara A, Asahara H, Igarashi A, Kamiyama Y, Nishimura G and Ogata T (2012) Complex genomic rearrangement in the SOX9 5′ region in a patient with Pierre Robin sequence and hypoplastic left scapula. Am J Med Genet A 158A:1529–1534.), brachydactyly-anonychia (Kurth et al., 2009Kurth I, Klopocki E, Stricker S, van Oosterwijk J, Vanek S, Altmann J, Santos HG, van Harssel JJT, de Ravel T, Wilkie AOM et al. (2009) Duplications of noncoding elements 5′ of SOX9 are associated with brachydactyly-anonychia. Nat Genet 41:862–863.), and congenital heart defects (Sanchez-Castro et al., 2013Sanchez-Castro M, Gordon CT, Petit F, Nord AS, Callier P, Andrieux J, Guérin P, Pichon O, David A, Abadie V et al. (2013) Congenital heart defects in patients with deletions upstream of SOX9. Hum Mutat 34:1628–1631.) have already been linked to pathological copy number variations of putative regulators of SOX9 expression in this chromosomal region.

Different studies have tried to establish genotypephenotype correlations in CD/ACD, but these have mostly remained elusive (Wagner et al., 1994Wagner T, Wirth J, Meyer J, Zabel B, Held M, Zimmer J, Pasantes J, Bricarelli FD, Keutel J, Hustert E et al. (1994) Autosomal sex reversal and campomelic dysplasia are caused by mutations in and around the SRY-related gene SOX9. Cell 79:1111–1120.; Meyer et al., 1997Meyer J, Südbeck P, Held M, Wagner T, Schmitz ML, Bricarelli FD, Eggermont E, Friedrich U, Haas OA, Kobelt A et al. (1997) Mutational analysis of the SOX9 gene in campomelic dysplasia and autosomal sex reversal: Lack of genotype/phenotype correlations. Hum Mol Genet 6:91–98.; Ninomiya et al., 2000Ninomiya S, Yokoyama Y, Teraoka M, Mori R, Inoue C, Yamashita S, Tamai H, Funato M and Seino Y (2000) A novel mutation (296 del G) of the SOX90 gene in a patient with campomelic syndrome and sex reversal. Clin Genet 58:224–227.; Pop et al., 2005Pop R, Zaragoza MV, Gaudette M, Dohrmann U and Scherer G (2005) A homozygous nonsense mutation in SOX9 in the dominant disorder campomelic dysplasia: A case of mitotic gene conversion. Hum Genet 117:43–53.). Mutations in SOX9 also display a great degree of variable expressivity (Cameron et al., 1996Cameron FJ, Hageman RM, Cooke-Yarborough C, Kwok C, Goodwin LL, Sillence DO and Sinclair AH (1996) A novel germ line mutation in SOX9 causes familial campomelic dysplasia and sex reversal. Hum Mol Genet 5:1625–1630.). Moreover, it has been demonstrated that patients with the same SOX9 mutation may develop CD or ACD, have different degrees of sexual development disorders, and even stark differences in survival (Wagner et al., 1994Wagner T, Wirth J, Meyer J, Zabel B, Held M, Zimmer J, Pasantes J, Bricarelli FD, Keutel J, Hustert E et al. (1994) Autosomal sex reversal and campomelic dysplasia are caused by mutations in and around the SRY-related gene SOX9. Cell 79:1111–1120.; Meyer et al., 1997Meyer J, Südbeck P, Held M, Wagner T, Schmitz ML, Bricarelli FD, Eggermont E, Friedrich U, Haas OA, Kobelt A et al. (1997) Mutational analysis of the SOX9 gene in campomelic dysplasia and autosomal sex reversal: Lack of genotype/phenotype correlations. Hum Mol Genet 6:91–98.; McDowall et al., 1999McDowall S, Argentaro A, Ranganathan S, Weller P, Mertin S, Mansour S, Tolmie J and Harley V (1999) Functional and structural studies of wild type SOX9 and mutations causing campomelic dysplasia. J Biol Chem 274:24023–24030.; Friedrich et al., 2000Friedrich U, Schaefer E, Meinecke P and Scherer G (2000) SOX9 mutation in a previously published case of campomelic dysplasia without overt campomelia. Clin Dysmorphol 9:233.; Moog et al., 2001Moog U, Jansen NJ, Scherer G, Schrander-Stumpel CT (2001) Acampomelic campomelic syndrome. Am J Med Genet 104:239–245.; Wada et al., 2009Wada Y, Nishimura G, Nagai T, Sawai H, Yoshikata M, Miyagawa S, Hanita T, Sato S, Hasegawa T, Ishikawa S et al. (2009) Mutation analysis of SOX9 and single copy number variant analysis of the upstream region in eight patients with campomelic dysplasia and acampomelic campomelic dysplasia. Am J Med Genet A 149A:2882–2885.).

Since changes in SOX9 associated with CD are mainly private mutations, the alterations identified here expand the spectrum of SOX9 pathogenic variations to about seventy (Table S3 Table S3 Compilation of all reported SOX9 mutations associated to CD and ACD. ) (Thong et al., 2000Thong MK, Scherer G, Kozlowski K, Haan E and Morris L (2000) Acampomelic campomelic dysplasia with SOX9 mutation. Am J Med Genet 93:421–425.; Giordano et al., 2001Giordano J, Prior HM, Bamforth JS and Walter MA (2001) Genetic study of SOX9 in a case of campomelic dysplasia. Am J Med Genet 98:176–181.; Preiss et al., 2001Preiss S, Argentaro A, Clayton A, John A, Jans DA, Ogata T, Nagai T, Barroso I, Schafer AJ and Harley VR (2001) Compound effects of point mutations causing campomelic dysplasia/autosomal sex reversal upon SOX9 structure, nuclear transport, DNA binding, and transcriptional activation. J Biol Chem 276:27864–27872.; Sock et al., 2003Sock E, Pagon RA, Keymolen K, Lissens W, Wegner M and Scherer G (2003) Loss of DNA-dependent dimerization of the transcription factor SOX9 as a cause for campomelic dysplasia. Hum Mol Genet 12:1439–1447.; Michel-Calemard et al., 2004Michel-Calemard L, Lesca G, Morel Y, Boggio D, Plauchu H and Attia-Sobol J (2004) Campomelic acampomelic dysplasia presenting with increased nuchal translucency in the first trimester. Prenat Diagn 24:519–523.; Hsiao et al., 2006Hsiao H-P, Tsai L-P, Chao M-C, Tseng H-I and Chang YC (2006) Novel SOX9 gene mutation in campomelic dysplasia with autosomal sex reversal. J Formos Med Assoc 105:1013–1016.; Shotelersuk et al., 2006Shotelersuk V, Jaruratanasirikul S, Sinthuwiwat T and Janjindamai W (2006) A novel nonsense mutation, E150X, in the SOX9 gene underlying campomelic dysplasia. Genet Mol Biol 29:617–620.; Beaulieu et al., 2009Beaulieu BM, Lemyre E, Rypens F, Scherer G, Lemieux N and Fournet J-C (2009) Diagnosis of true hermaphroditism in a fetus with acampomelic campomelic dysplasia. Prenat Diagn 29:528–530.; Gentilin et al., 2010Gentilin B, Forzano F, Bedeschi MF, Rizzuti T, Faravelli F, Izzi C, Lituania M, Rodriguez-Perez C, Bondioni MP, Savoldi G et al. (2010) Phenotype of five cases of prenatally diagnosed campomelic dysplasia harboring novel mutations of the SOX9 gene. Ultrasound Obstet Gynecol 36:315–323.; Okamoto et al., 2010Okamoto T, Nakamura E, Nagaya K, Hayashi T, Mukai T and Fujieda K (2010) Patient reports: Two novel frameshift mutations in the SOX9 gene in two patients with campomelic dysplasia who showed long-term survival. J Pediatr Endocrinol Metab 23:1189–1193.; Staffler et al., 2010Staffler A, Hammel M, Wahlbuhl M, Bidlingmaier C, Flemmer AW, Pagel P, Nicolai T, Wegner M and Holzinger A (2010) Heterozygous SOX9 mutations allowing for residual DNA-binding and transcriptional activation lead to the acampomelic variant of campomelic dysplasia. Hum Mutat 31:E1436–1444.; Kim et al., 2011Kim H-Y, Yoon CH, Kim G-H, Yoo H-W, Lee BS, Kim KS and Kim EA-R (2011) A case of campomelic dysplasia without sex reversal. J Korean Med Sci 26:143–145.; Stoeva et al., 2011Stoeva R, Grozdanova L, Scherer G, Krasteva M, Bausch E, Krastev T, Linev A and Stefanova M (2011) A novel SOX9 nonsense mutation, q401x, in a case of campomelic dysplasia with XY sex reversal. Genet Couns 22:49–53.; Chen et al., 2012Chen S-Y, Lin S-J, Tsai L-P and Chou Y-Y (2012) Sex-reversed acampomelic campomelic dysplasia with a homozygous deletion mutation in SOX9 gene. Urology 79:908–911.; Gopakumar et al., 2013Gopakumar H, Superti-Furga A, Unger S, Scherer G, Rajiv PK and Nampoothiri S (2013) Acampomelic Form of Campomelic Dysplasia with SOX9 Missense Mutation. Indian J Pediatr 81:98–100.; Matsushita et al., 2013Matsushita M, Kitoh H, Kaneko H, Mishima K, Kadono I, Ishiguro N and Nishimura G (2013) A novel SOX9 H169Q mutation in a family with overlapping phenotype of mild campomelic dysplasia and small patella syndrome. Am J Med Genet A 161:2528–2534.; Tonni et al., 2013Tonni G, Ventura A, Pattacini P, Bonasoni MP and Baffico AM (2013) p.His165Pro: A novel SOX9 missense mutation of campomelic dysplasia. J Obstet Gynaecol Res 39:1085–1091.). Premature termination codons (PTCs) are the most prevalent mutational class in CD, accounting for approximately 45% of all the alterations identified. Consistently, six of the nine patients (67%) in our series had a PTC mutation. In these cases, non-sense mediated mRNA decay (NMD) could potentially be employed to prevent translation of truncated peptides (Chang et al., 2007Chang Y-F, Imam JS and Wilkinson MF (2007) The nonsense-mediated decay RNA surveillance pathway. Annu Rev Biochem 76:51–74.). Even if expression from the mutated alleles escaped NMD, these would generate SOX9 proteins lacking all, or at least some, of the essential domains for proper protein activity (Figure S1 Figure S1 Putative SOX9 proteins resultant from the premature stop codon mutations identified in six CD patients. ).

Since truncated SOX9 polypeptides have been shown to retain some residual activity (Cameron et al., 1996Cameron FJ, Hageman RM, Cooke-Yarborough C, Kwok C, Goodwin LL, Sillence DO and Sinclair AH (1996) A novel germ line mutation in SOX9 causes familial campomelic dysplasia and sex reversal. Hum Mol Genet 5:1625–1630.), different authors have associated larger protein truncations with greater life expectancy of CD patients (Meyer et al., 1997Meyer J, Südbeck P, Held M, Wagner T, Schmitz ML, Bricarelli FD, Eggermont E, Friedrich U, Haas OA, Kobelt A et al. (1997) Mutational analysis of the SOX9 gene in campomelic dysplasia and autosomal sex reversal: Lack of genotype/phenotype correlations. Hum Mol Genet 6:91–98.; Pop et al., 2005Pop R, Zaragoza MV, Gaudette M, Dohrmann U and Scherer G (2005) A homozygous nonsense mutation in SOX9 in the dominant disorder campomelic dysplasia: A case of mitotic gene conversion. Hum Genet 117:43–53.). In this cohort, patient 1 would, theoretically, retain the largest portion of SOX9, with approximately 54% of the wild-type peptide. However, this observation did not translate into less severity, because we did not identify any correlation between the identified mutations and survival of patients.

Splice-site mutations in SOX9 account for approximately only 4% of CD mutations reported to date (see Table S3 Table S3 Compilation of all reported SOX9 mutations associated to CD and ACD. ). Only one patient in this series had a splice-site mutation. This gives rise to an A-to-G transition at nucleotide position -2 from the acceptor splice-site of intron 1 (IVS1-2A > G), which was predicted in silico to affect splicing with a probability of 67%. Kwok et al. (1995)Kwok C, Weller PA, Guioli S, Foster JW, Mansour S, Zuffardi O, Punnett HH, Dominguez-Steglich MA, Brook JD and Young ID (1995) Mutations in SOX9, the gene responsible for campomelic dysplasia and autosomal sex reversal. Am J Hum Genet 57:1028–1036. identified an A-to-C transition at the same nucleotide position -2 in a female infant with typical CD findings and 46,XY karyotype (Kwok et al., 1995Kwok C, Weller PA, Guioli S, Foster JW, Mansour S, Zuffardi O, Punnett HH, Dominguez-Steglich MA, Brook JD and Young ID (1995) Mutations in SOX9, the gene responsible for campomelic dysplasia and autosomal sex reversal. Am J Hum Genet 57:1028–1036.). Our patient had a normal 46, XX karyotype.

Interestingly, while many studies report mutations in the coding sequence of SOX9 in 46,XY sex-reversed CD individuals, we did not identify any nucleotide alteration in a patient with sex-reversal. CD patients were observed to encode mutations of any of the mutational classes already described (see Table S3 Table S3 Compilation of all reported SOX9 mutations associated to CD and ACD. ). Some researchers argue that sex reversal may be a phenotype with incomplete penetrance (Meyer et al., 1997Meyer J, Südbeck P, Held M, Wagner T, Schmitz ML, Bricarelli FD, Eggermont E, Friedrich U, Haas OA, Kobelt A et al. (1997) Mutational analysis of the SOX9 gene in campomelic dysplasia and autosomal sex reversal: Lack of genotype/phenotype correlations. Hum Mol Genet 6:91–98.), but this proposition needs further support. Further investigations of the molecular basis of CD and related disorders are likely to contribute to a better understanding of the physiological roles of SOX9, which is a key transcription factor in the early embryonic development of several tissues.

Supplementary Material

Table S1

Detailed clinical evaluation of CD patients included in the study.

Table S2

Detailed radiological evaluation of CD patients included in the study.

Table S3

Compilation of all reported SOX9 mutations associated to CD and ACD.

Figure S1

Putative SOX9 proteins resultant from the premature stop codon mutations identified in six CD patients.

The following online material is available for this article:
  • Table S1 - Detailed clinical evaluation of CD patients included in the study.

  • Table S2 - Detailed radiological evaluation of CD patients included in the study.

  • Table S3 - Compilation of all reported SOX9 mutations associated to CD and ACD.

  • Figure S1 - Putative SOX9 proteins resultant from the premature stop codon mutations identified in six CD patients.

This material is available as part of the online article from http://www.scielo.br/gmb.

The authors would like to thank the patients and their families for participating in this study. The technical assistance of Dr. Sandra Leistner Segal (Medical Genetics Service, HCPA) for ZFX/SRY genotyping is greatly appreciated. Financial support was partially provided by the Grupo de Pesquisa e Pós-Graduação do Hospital de Clínicas de Porto Alegre (grant 12-0467 to EPM, MTVS and LS-F) and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (grants 402008/2010-3 and 590148/2011-7 to DPC).

  • Associate Editor: Maria Luiza Petzl-Erler

References

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Internet Resources

Publication Dates

  • Publication in this collection
    Jan-Mar 2015

History

  • Received
    08 May 2014
  • Accepted
    19 Aug 2014
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