Hypochondroplasia

Hypochondroplasia is an autosomal dominant discrete form of short-limbed dwarfism with roentgenographic changes similar to, but distinctive from, achondroplasia. The patients are normal at birth and in early childhood present with short-limbed dwarfism, thick body build, long trunk, normal head, moderate lumbar lordosis and broad, stubby hands and feet. A high incidence of mental retardation and absence of other neurologic complications is distinctive from achondroplasia. Diagnosis of hypochondroplasia is primarily radiogrpahic. No single diagnostic radiographic sign is present, and thus, a complete radiographic survey of the whole skeleton is required for diagnosis. Pertinent radiographic findings include a normal skull, short, broad long bones with prominent bony sites of muscle attachment, normal growth plate, prominent styloid process of the ulna and lateral malleolus of the fibula, shortened base of the iliac bones, horizontal hypoplastic low-set sacrum and mild narrowing of the interpediculate distance of the lumbar spine. Differential diagnosis is from other types of short-limbed dwarfism, particularly achondroplasia. Kozlowski, an authority on hypochondroplasia, believes this form of short-limbed dwarfism, if carfully searched for, may be more common than achondroplasia.