Multiple epiphyseal dysplasia, Fairbank type: morphologic and biochemical study of cartilage.

We have performed histochemical, immunohistochemical, electron microscopic, and biochemical studies on the upper tibial cartilage from a case of multiple epiphyseal dysplasia, Fairbank type. Most chondrocytes had intracytoplasmic inclusions which took the stains for proteins and were resistant to microbial collagenase digestion. The electron microscopic study showed that the inclusions are dilatations of the rough endoplasmic reticulum containing a material with alternately wide electron dense and electron lucent layers. Both in optical and in electron microscopy the inclusions fixed antibodies against the core protein of the large cartilage proteoglycans (aggrecans). They didn't stain with antibodies against type II collagen. The gel electrophoretic pattern of the large proteoglycans was different from normal controls. The morphologic and biochemical alterations found in multiple epiphyseal dysplasia are similar to those already described in pseudoachondroplasia (Stanescu et al.: Eur J Pediatr 138:121-225, 1982; Stanescu et al.: J Bone Joint Surg 66A:817-836, 1984). However, the inclusions are smaller and the growth cartilage much less disorganized in multiple epiphyseal dysplasia. The similarity of morphologic and biochemical abnormalities strongly suggests that the two diseases have a similar pathogenesis and belong to the same bone dysplasia family.