A Heterozygous Mutation in the Triple Helical Region of the Alpha 1 (II) Chain of the COL2A1 Protein Causes Non-lethal Spondyloepiphyseal Dysplasia Congenita.

Objective: Heterozygous pathogenic variants in the COL2A1 gene result in several clinical features including impaired skeletal growth, ocular and otolaryngological abnormalities. Missense mutations, specifically, a c.1357G>A (p.G453S) in the triple helical region of COL2A1 protein causes lethal spondyloepiphyseal dysplasia (SED), a form of hypochondrogenesis. In this study, we aimed to identify the underlying cause of a case of SED congenita (SEDC) in a 27-month-old child. Materials and Methods: A patient who was diagnosed initially as an osteochondrodysplasia underwent a detailed clinical and radiological examination to obtain a conclusive diagnosis. The patient did not show any clinical features of hypochondrogenesis. Whole exome sequencing of the COL2A1 gene was carried out to identify the underlying genetic cause of the disorder. Results: Variant annotation and filtration detected a heterozygous missense mutation c.1357G>A (p.G453S) in the exon 21 of the COL2A1 gene of the proband which was confirmed by Sanger sequencing. Neither parent carried the mvariant suggesting this was a new mutation. Conclusion: The COL2A1 mutation (c.1357G>A), identified in this case, results in more mild phenotype than other missense mutations in exon 21 which are known to cause lethal hypochondrogenesis. We showed, for the first time, that missense mutation (p.G453S) in the triple helical region of the alpha 1 (II) chain of the COL2A1 protein underlies SEDC and is not always lethal.