Genetic mapping of a locus for multiple epiphyseal dysplasia (EDM2) to a region of chromosome 1 containing a type IX collagen gene.

Multiple epiphyseal dysplasia (MED) is a dominantly inherited chondrodysplasia characterized by mild short stature and early-onset osteoarthrosis. Some forms of MED clinically resemble another chondrodysplasia phenotype, the mild form of pseudoachondroplasia (PSACH). On the basis of their clinical similarities as well as similar ultrastructural and biochemical features in cartilage from some patients, it has been proposed that MED and PSACH belong to a single bone-dysplasia family. Recently, both mild and severe PSACH as well as a form of MED have been linked to the same interval on chromosome 19, suggesting that they may be allelic disorders. Linkage studies with the chromosome 19 markers were carried out in a large family with MED and excluded the previously identified interval. Using this family, we have identified an MED locus on the short arm of chromosome 1, in a region containing the gene (COL9A2) that encodes the alpha 2 chain of type IX collagen, a structural component of the cartilage extracellular matrix.

Mutation screening by a combination of biotin-SSCP and direct sequencing.

We have developed a mutation detection strategy that combines single strand conformational polymorphism (SSCP) analysis of one strand of a double-stranded amplification product with direct sequencing of the other. Using this strategy, which we find economical of both time and resources, we have identified a G to A transition, which substitutes a serine for glycine residue at position 862 in the major helix of the alpha 1 chain of Type I collagen. We use this mutation, which causes a lethal form of osteogenesis imperfecta, to illustrate the technique.