Type II achondrogenesis-hypochondrogenesis: Identification of abnormal type II collagen

We have extended the study of a mild case of type II achondrogenesis-hypochondrogenesis to include biochemical analyses of cartilage, bone, and the collagens produced by dermal fibroblasts. Type I collagen extracted from bone and types I and III collagen produced by dermal fibroblasts were normal, as was the hexosamine ratio of cartilage proteoglycans. Hyaline cartilage, however, contained approximately equal amounts of types I and II collagen and decreased amounts of type XI collagen. Unlike the normal SDS-PAGE mobility of coextracted types I and XI collagen chains, type II collagen chains exhibited retarded mobility. Two-dimensional SDS-PAGE revealed extensive overmodification of all type II cyanogen bromide peptides in a pattern consistent with heterozygosity for an abnormal proα1(II) chain which impaired the assembly and/or folding of type II collagen. This interpretation implies that dominant mutations of the COL2A1 gene may cause type II achondrogenesis-hypochondrogenesis. More generally, emerging data implicating defects of type II collagen in the type II achondrogenesis-hypochondrogenesis-spondyloepiphyseal dysplasia congenita spectrum and in the Kniest-Stickler syndrome spectrum suggest that diverse mutations of this gene may be associated with widely differing phenotypic outcome.