Acampomelic form of campomelic dysplasia with SOX9 missense mutation

A review of skeletal dysplasia research in India

We aimed to review the contributions by Indian researchers to the subspecialty of skeletal dysplasias (SDs). Literature search using specific keywords in PubMed was performed to retrieve all the published literature on SDs as on July 6, 2017. All published literature on SDs wherein at least one author was from an Indian institute was included. Publications were grouped into different categories based on the major emphasis of the research paper. Five hundred and forty publications in English language were retrieved and categorized into five different groups. The publications were categorized as reports based on: (i) phenotypes (n = 437), (ii) mutations (n = 51), (iii) novel genes (n = 9), (iv) therapeutic interventions (n = 31), and (v) reviews (n = 12). Most of the publications were single-patient case reports describing the clinical and radiological features of the patients affected with SDs (n = 352). We enlisted all the significant Indian contributions. We have also highlighted the reports in which Indians have contributed to discovery of new genes and phenotypes. This review highlights the substantial Indian contributions to SD research, which is poised to reach even greater heights given the size and structure of our population, technological advances, and expanding national and international collaborations.

The ontogeny of Robin sequence

The triad of micrognathia, glossoptosis, and concomitant airway obstruction defined as "Robin sequence" (RS) is caused by oropharyngeal developmental events constrained by a reduced stomadeal space. This sequence of abnormal embryonic development also results in an anatomical configuration that might predispose the fetus to a cleft palate. RS is heterogeneous and many different etiologies have been described including syndromic, RS-plus, and isolated forms. For an optimal diagnosis, subsequent treatment and prognosis, a thorough understanding of the embryology and pathogenesis is necessary. This manuscript provides an update about our current understanding of the development of the mandible, tongue, and palate and possible mechanisms involved in the development of RS. Additionally, we provide the reader with an up-to-date summary of the different etiologies of this phenotype and link this to the embryologic, developmental, and genetic mechanisms.

A mutation creating an upstream initiation codon in the SOX9 5' UTR causes acampomelic campomelic dysplasia

Background

Campomelic dysplasia (CD) is a semilethal developmental disorder caused by mutations in and around SOX9. CD is characterized by multiple skeletal malformations including bending (campomelia) of long bones. Surviving patients frequently have the acampomelic form of CD (ACD).

Methods

This is a single case report on a patient with clinical and radiological features of ACD who has no mutation in the SOX9 protein‐coding sequence nor a translocation with breakpoint in the SOX9 regulatory domain. We include functional studies of the novel mutant protein in vitro and in cultured cells.

Results

The patient was found to have a de novo heterozygous mutation c.‐185G>A in the SOX9 5′UTR. The mutation creates an upstream translation start codon, uAUG, with a much better fit of its flanking sequence to the Kozak consensus than the wild‐type AUG. By in vitro transcription‐translation and transient transfection into COS‐7 cells, we show that the uAUG leads to translation of a short peptide from a reading frame that terminates just after the wild‐type AUG start codon. This results in reduced translation of the wild‐type protein, compatible with the milder phenotype of the patient.

Conclusion

Findings support the notion that more mildly affected, surviving CD/ACD patients carry mutant SOX9 alleles with residual expression of SOX9 wild‐type protein. Although rarely described in human genetic disease and for the first time here for CD, mutations creating upstream AUG codons may be more common than generally assumed.

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

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.