Both multiple epiphyseal dysplasia (MED) and psudoachondroplasia (PSACH) are characterized by short limbed dwarfism, identifiable during childhood, with a normal face and head. Skeletal findings in MED include epiphyseal dysplasia, hip dysplasia and degenerative arthritic changes, brachydactyly with shortened metacarpals and phalanges, and hyperextensible finger joints. Findings in PSACH are typically more severe and include lordosis, kyphosis, and scoliosis as well as other vertebral/spinal anomalies and a waddling gait. In addition, brachydactyly and “telescoping” fingers, ulnar deviation of the wrists; short tubular bones, fragmented epiphyses and irregular mushroomed metaphyses, limited elbow and hip extension, lax ligaments, genu valgum, varum, and recurvatum may be seen. Cervical cord compression myelopathy is a complication of this condition. Clinical diagnosis in these disorders may be difficult due to the absence of characteristic facial features (in contrast to achondroplasia) and the fact that growth retardation may not be apparent until the second year of life. Mutation in the COMP gene (cartilage oligomeric matrix protein), a member of the thrombospondin gene family, underly both disorders, as they are allelic. Almost all cases of PSACH are thought to be due to mutation in COMP, and approximately 80% of classical MED cases are a result of a mutation in this gene. The COMP gene encompasses 19 exons. Exons 4-19, which encode the EGF-like (type II) repeats, calmodulin-like (type III) repeats, and the C-terminal domain, correspond in sequence and intron location to the thrombospondin genes, while exons 1-3 are unique to COMP.