What is Thanatophoric Dysplasia?

Thanatophoric dysplasia is a fatal skeletal abnormality that is considered a variation of dwarfism. Dysplasia is a term that describes the presence of a developmental abnormality. The term thanatophoric is a Greek word that means “death bringing” and refers to the fact that this condition is always fatal. An infant with thanatophoric dysplasia typically will die within just a few hours of birth. This genetic disorder occurs in equal numbers in male and female children, at a rate of approximately one in 20,000 to 50,000 births.

Thanatophoric dysplasia is caused by a mutation in a gene called FGFR3. This is not, however, a hereditary disorder, and a parent cannot have this condition and pass it directly to a child. Instead, the mutation that causes this condition is known as a de novo mutation, which means that it occurs spontaneously during the production of sperm or eggs. The mutation in the gene FGFR3 leads to dysfunctional bone growth, causing a characteristic array of growth abnormalities.

The physical signs of thanatophoric dysplasia can be seen immediately after birth. These include severely shortened limbs, a narrow trunk, a protruding abdomen and a condition called macrocephaly, in which the head is larger than normal. The infant also is much smaller than normal, with an average length of approximately 16 inches (40 cm). In addition, hypotonia, or generalized muscle weakness, is a feature of babies born with this disorder.

Before birth, certain features of this disorder can be seen upon ultrasound examination of the fetus. Growth deficiency, particularly of the limbs; macrocephaly; bowed femurs; a narrow chest cavity; and shortened ribs can be seen on an ultrasound when a fetus is affected by thanatophoric dysplasia. Despite the characteristic appearance of these symptoms, it often is difficult to conclusively diagnose the disorder by ultrasound alone.

Children who are born with this disorder cannot survive without extensive and aggressive inpatient medical care. Most of these children have significant respiratory distress at birth and must be admitted to an intensive neonatal unit for intubation and monitoring. Depending on the needs of the child, medication might be used to alleviate medical conditions that arise as a result of the dysplasia. In cases where parents do not wish to follow an aggressive course of treatment, the child is fed and kept comfortable for as long as he or she survives.

Even with aggressive treatment, however, it is rare for a child with this disorder to live more than a few hours after birth. In the rare event that a child does survive, he or she is admitted to a long-term care unit, because inpatient care is needed for an extended period before the child can be taken home. Complications such as severe developmental delay, growth delay and seizures are likely for children who survive the neonatal period. A child who survives the neonatal period might live for a year or two before succumbing to fatal respiratory complications.