Thanatophoric dysplasia is a severe skeletal disorder characterized by extremely short limbs and folds of extra skin on the arms and legs. Other features of this condition include a narrow chest, short ribs, underdeveloped lungs, and an enlarged head with a large forehead and prominent, wide-spaced eyes. Most infants with thanatophoric dysplasia are stillborn or die shortly after birth from respiratory failure. A few affected individuals have survived into childhood with extensive medical help. Thanatophoric dysplasia is caused by mutations in the FGFR3 gene. While this condition is considered to be autosomal dominant, virtually all cases have occurred in people with no history of the disorder in their family.Two major forms of thanatophoric dysplasia have been described, type I and type II. Type I thanatophoric dysplasia is distinguished by the presence of curved thigh bones and flattened bones of the spine (platyspondyly). Type II thanatophoric dysplasia is characterized by straight thigh bones and a moderate to severe skull abnormality called a cloverleaf skull.

FGFR3 gene. This gene provides instructions for making a protein that is involved in the development and maintenance of bone and brain tissue. Mutations in this gene cause the FGFR3 protein to be overly active, which leads to the severe problems with bone growth that are seen in thanatophoric dysplasia. It is not known how FGFR3 mutations cause the brain and skin abnormalities associated with this disorder.

FGFR3 gene in each cell causes the condition. However, almost all cases of thanatophoric dysplasia are caused by new mutations in the FGFR3 gene and occur in people with no history of the disorder in their family. No affected individuals are known to have had children, so the disorder has not been passed to the next generation.