Focal dermal hypoplasia is a genetic disorder that primarily affects the skin, skeleton, eyes, and face. About 90 percent of affected individuals are female. Males usually have milder signs and symptoms than females. Although intelligence is typically unaffected, some individuals have intellectual disability.

Mutations in the PORCN gene cause focal dermal hypoplasia. This gene provides instructions for making a protein that is responsible for modifying other proteins, called Wnt proteins. Wnt proteins participate in chemical signaling pathways in the body that regulate development of the skin, bones, and other structures before birth.

Focal dermal hypoplasia appears to be a rare condition, although its exact prevalence is unknown.

Focal dermal hypoplasia is inherited in an X-linked dominant pattern. The gene associated with this condition is located on the X chromosome, which is one of the two sex chromosomes. In females (who have two X chromosomes), a mutation in one of the two copies of the gene in each cell is sufficient to cause the disorder. The X chromosome that contains the mutated PORCN gene may be turned on (active) or turned off (inactive) due to a process called X-inactivation. Early in embryonic development in females, one of the two X chromosomes is permanently inactivated in somatic cells (cells other than egg and sperm cells). X-inactivation ensures that females, like males, have only one active copy of the X chromosome in each body cell. Usually X-inactivation occurs randomly, so that each X chromosome is active in about half the body's cells. Sometimes X-inactivation is not random, and one X chromosome is active in more than half of cells. When X-inactivation does not occur randomly, it is called skewed X-inactivation. Researchers suspect that the distribution of active and inactive X chromosomes may play a role in determining the severity of focal dermal hypoplasia in females.

Published Date: July 01, 2014
Published By: National Institutes of Health