Novel and recurrent COMP (cartilage oligomeric matrix protein) mutations in pseudoachondroplasia and multiple epiphyseal dysplasia

S. Ikegawa, Hirofumi Ohashi, Gen Nishimura, Kyoung Chang Kim, Akio Sannohe, Mamori Kimizuka, Yoshimitsu Fukushima, Toshiro Nagai, Yusuke Nakamura

Pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED) are common skeletal dysplasias with impaired enchondral ossification and premature degenerative joint disease. The two disorders were in the past considered to be distinct clinical entities; however, recent studies have proven that both diseases can result from mutations of the gene encoding cartilage oligomeric matrix protein (COMP). To characterize further COMP mutations and investigate phenotype-genotype relationships, we screened this gene in 15 patients with PSACH or MED by directly sequencing polymerase chain reaction products from genomic DNA. We identified ten mutations involving conserved residues among the eight calmodulin-like repeats of the gene product: seven were novel missense mutations in exons 9, 10, 11, 13 or 14, and the other three resulted from deletion of one of the five GAC repeats in exon 13. We have found that the GAC repeats in the 7th calmodulin-like repeat in exon 13 represent a hot-spot for mutation, and that mutations in the 7th calmodulin-like repeat produce severe PSACH phenotypes while mutations elsewhere in the gene exhibit mild PSACH or MED phenotypes. These genotype-phenotype correlations may facilitate molecular diagnosis and classification of PSACH and MED, and provide insight into the relationship between structure and function of the COMP gene product.