Chapter 695 Primary Chondrodystrophy (Metaphyseal Dysplasia)

Skeletal dysplasias fall under 3 major subgroupings: osteodysplasias, chondrodysplasias, and dysostoses. The osteodysplasias affect bone density and often lead to osteopenia. The chondrodysplasias are genetic disorders of cartilage and result in deficient linear growth. The dysostoses affect a single bone.

In primary chondrodystrophy, which is an autosomal dominant condition, bowing of the legs, short stature, and a waddling gait appear in the absence of abnormalities of serum levels of calcium and phosphate, alkaline phosphatase activity, or vitamin D metabolites. Metaphyseal chondrodysplasia (Jansen type) is typified by cupped and ragged metaphyses, which develop mottled calcification at the distal ends of bone over time (Fig. 695-1). Hypercalcemia, with serum values of 13-15 mg/dL, can occur. The spine can also be deformed by the irregular growth of vertebrae. Three different mutations have been identified in parathyroid hormone receptor type I as the molecular cause of this syndrome, as have some of the downstream target genes that can contribute to the pathogenesis of the disease. The Schmid type

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