Novel amino acid substitution in the Y-position of collagen type II causes spondyloepimetaphyseal dysplasia congenita.

We report on monozygotic twins with short stature and severe spondyloepimetaphyseal dysplasia congenita (SEMDC) from the Polish population. Phenotype of the twin girls resembles spondyloepiphyseal dysplasia congenita Spranger-Wiedemann (SEDC-SW), but shortening of the stature is more severe and the cranioface is normal. The distinctive radiographic features, in spite of similarity to SEDC-SW, indicate different spinal and, notably, severe metaphyseal involvement. Molecular analysis of the COL2A1 gene revealed an A to G transition at nucleotide +79 of exon 41 that converted the codon for arginine at amino acid 792 to a codon for glycine (Arg792Gly). The twins were heterozygous for the mutation and neither parent had this change. The Arg792Gly substitution is located at the Y-position of Gly-X-Y triplet, and it is likely that this substitution decreased the thermal stability of the triple helix and may affect fibril growth by replacement of an arginine residue, which is important for a conformation of the triple helix.