The expression of type X collagen is restricted to hypertrophic chondrocytes in regions undergoing endochondral ossification, such as growth plates. The precise function of type X collagen is unknown but the tissue-specific expression prompted us to examine the gene in hereditary disorders of cartilage and bone growth (osteochondrodysplasias). We have identified a 13 base pair deletion in one type X collagen allele segregating with autosomal dominant Schmid metaphyseal chondrodysplasia in a large Mormon kindred (lod score= 18.2 at θ = 0). The mutation produces a frameshifl which alters the highly conserved C-terminal domain of the α1(X) chain and reduces the length of the polypeptide by nine residues. This mutation may prevent association of the mutant polypeptide during trimer formation, resulting in a decreased amount of normal protein.
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