Editor—Pseudoachondroplasia (PSACH) is an autosomal dominant chondrodysplasia. In the majority of clinically defined cases, mutations have been identified in the gene encoding cartilage oligomeric matrix protein (COMP).1 Mutations in theCOMP gene have also been identified in some forms of multiple epiphyseal dysplasia (MED), a related skeletal dysplasia.1 All of the mutations associated with PSACH and MED have been found in exons encoding the type III repeat region or C-terminal domain of COMP.

Clinically, PSACH is characterised by short limbed dwarfism, which first becomes apparent in infancy, short fingers, ligamentous laxity, scoliosis, and early onset osteoarthritis (OA).2Radiographic features include small irregular epiphyses with delayed ossification, flared metaphyses, anterior beaking of the vertebral bodies, and delayed maturation of the triradiate cartilage and acetabulum.3

We report three patients who had previously been given erroneous diagnoses, in whom mutations in exon 13 of theCOMP gene have been identified. This emphasises the utility of molecular diagnosis, particularly in adult patients where radiological diagnosis can be difficult.

All three affected subjects were born to unaffected parents. Each was of normal intelligence and normal facial appearance.

Case 1 presented at 5 years because of pain in both hips. Numerous diagnoses, including spondyloepiphyseal dysplasia congenita with coxa vara and Morquio's syndrome, were considered followingx ray examination. Extensive surgery over the following years included a left femoral osteotomy and bilateral Girdlestones operations to treat her osteoarthritis. She has had two unaffected children. Examination at 65 years showed her height at 136 cm (<3rd centile), reduced …