Hypochondroplasia.

Hypochondroplasia is a hereditary form of short-limbed dwarfism which somewhat resembles achondroplasia, but which is clinically, roentgenographically, and genetically distinct. The pertinent findings in 6 new cases are: moderate rhizomelic shortness of stature; normal craniofacial appearance and hand configuration; and later recognition of the presence of the abnormality than in achondroplasia (which can be recognized at birth). A review of the 35 previously described cases in the literature reveals a preponderance of affected females and a high incidence of spontaneous mutation, although when once evident the trait is passed as an autosomal dominant. Two of our patients had seizures, and mental deficiency may be an associated finding although it is by no means usually present. Orthopedists should be aware of this entity, which may be somewhat more common than has been thought, because of the different implications for ultimate height, which is greater in hypochondroplasia than in achondroplasia, the lack of cauda equina compression findings, and the need for genetic counseling.