Hypochondroplasia is characterized by disproportionate short stature, mild lumbar lordosis and limited extension of the elbow joints. Prevalence is estimated at around 1 in 33,000. The clinical manifestations generally become apparent during childhood. Bowlegs may also be present. Facial dysmorphism, orthopedic malformations and neurologic problems are not features of hypochondroplasia. An association with intellectual deficit has been reported. The disorder is transmitted in an autosomal dominant manner and is caused by mutations in the fibroblast growth factor receptor-3 gene (FGFR3; 4p16.3). Typical radiological findings in hypochondroplasia include moderate narrowing of the interpeduncular distances, shortened tubular bones with distal lengthening of the fibula, and short and broad femoral necks. Hypochondroplasia closely resembles achondroplasia (also caused by mutations in the FGFR3 gene; see this term), although the short stature and skeletal disproportion are clearly less pronounced in hypochondroplasia and the two conditions can be differentiated on the basis of the milder radiological findings in hypochondroplasia. Treatment is symptomatic only. Final adult height varies between 132 and 147 cm and life expectancy is normal.
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