Novel mutation in exon 18 of the cartilage oligomeric matrix protein gene causes a severe pseudoachondroplasia

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Abstract
Pseudoachondroplasia (PSACH) is a common skeletal dysplasia characterized by disproportionate short stature, early‐onset osteoarthrosis, and dysplasia of the spine, epiphysis, and metaphysis. Multiple epiphyseal dysplasia (MED) is a similar but less severe disorder characterized by dysplasia of the epiphysis. Both disorders are caused by mutations in the cartilage oligomeric matrix protein (COMP) gene. COMP mutations cluster in a region of the gene that encodes calmodulin‐like repeats (CLRs) and correlate closely with disease severity. Typically, mutations in exon 13 that composes the seventh CLR produce severe PSACH phenotypes, whereas mutations found elsewhere in the gene produce mild PSACH or MED phenotypes. We have identified a PSACH patient carrying a novel mutation in exon 18 of COMP that composes the C‐terminal globular domain. This mutation produced a severe PSACH phenotype with marked short stature and deformities of the spine and extremities. Our results extend the range of disease‐causing mutations within the COMP gene and demonstrate the importance of the additional domain of COMP protein in its in vivo function.