Schmid type metaphyseal chondrodysplasia: a spondylometaphyseal dysplasia identical to the "Japanese" type

Background. Schmid-type metaphyseal chondrodysplasia (Schmid MCD) is an aut osomal dominant chondrodysplasia resulting from various mutations in the CO L10A1 gene. This disorder has been well delineated at a clinical level and has been classified radiographically as a pure metaphyseal chondrodysplasia . A missense mutation in the COL10A1 gene has also been shown to cause a ra re spondylo-metaphyseal chondrodysplasia (SMD) named the "Japanese" type wh ich, apart from exhibiting a mild spinal phenotype, shares striking clinica l and radiographic similarities to Schmid MCD. Objective. The clinical, rad iographic and molecular similarities between Schmid MCD and Japanese SMD le d to the hypothesis that these conditions could be identical type X collage nopathies. Materials and methods. We analyzed 33 cases of typical Schmid MCD from the International Skeletal Dysplasia Registry, looking specifically for any rad iographic evidence of spinal involvement. Results. We found that in 9.1% (3/33) of cases reviewed there was definite radiographic evidence of spinal involvement comprising mild platyspondyly, vertebral body abnormalities, and end-plate irregularity. Conclusion. These data indicate that spinal changes are an uncommon but var iable component of Schmid MCD and that this condition and "Japanese" SMD ar e identical collagen type X disorders. Furthermore, the fact that the speci fic mutation reported in the family with Japanese type SMD, resulting in th e substitution of a glutamic acid residue for a glycine at codon 595 (G595 E), has also been reported in a patient with Schmid MCD strongly supports t his conclusion.