MED, COMP, multilayered and NEIN: an overview of multiple epiphyseal dysplasia.

This overview covers the group of disorders that presents radiographically as multiple epiphyseal dysplasia (MED). The disorders include "classic MED" (Ribbing and Fairbank types): MED that is caused by mutations in the cartilage oligomeric matrix protein (COMP), type IX collagen, and matrilin 3 genes (MATN3); and MED with multilayered patella, brachydactyly, and clubbed feet resultant from mutations in gene defect diastrophic dysplasia (DTDST). The recently identified gene/molecular abnormalities in these disorders have made more exact identification possible in many cases, although clinical testing is not always available. However, there are specific radiographic findings that allow the accurate diagnosis to be made, thus potentially guiding which molecular defect(s) should be investigated. The modes of inheritance of these distinct MED conditions are not identical. When a specific diagnosis is made, proper genetic counseling as well as prognostication, management issues and complications can be delineated to the patient and family. This review will include the mechanics of diagnostic and molecular triage for these disorders.