Thanatophoric dysplasia type I.

Thanatophoric dysplasia is a sporadic, nearly always lethal congenital skeletal dysplasia. It is characterized by shortening of the limbs, a severely small thorax, macrocephaly, and platyspondyly. There are two major subtypes: a short, curved femur characterizes type I, and a straighter femur with cloverleaf skull characterizes type II. Recently, mutations in the fibroblast growth factor receptor 3 (FGFR-3) gene have been identified in both subtypes, which suggest that thanatophoric dysplasia is a genetically homogenous skeletal disorder. Most affected neonates die of respiratory failure, due to narrow thorax with pulmonary hypoplasia. Antenatal sonographic diagnosis is feasible in the second trimester of pregnancy, but differentiating thanatophoric dysplasia from non-lethal skeletal disorders is very important. At the present time, however, prenatal genetic screening seems unpractical.