Fumarase deficiency is a condition that primarily affects the nervous system, especially the brain.
Fumarase deficiency is a very rare disorder. Approximately 100 affected individuals have been reported worldwide. Several were born in an isolated religious community in the southwestern United States.
Fumarase deficiency is caused by mutations in the FH gene. This gene provides instructions for making an enzyme called fumarase (also known as fumarate hydratase). Fumarase participates in an important series of reactions known as the citric acid cycle or Krebs cycle, which allows cells to use oxygen and generate energy. Specifically, fumarase helps convert a molecule called fumarate to a molecule called malate.
Mutations in the FH gene disrupt the enzyme's ability to help convert fumarate to malate, interfering with the function of this reaction in the citric acid cycle. Impairment of the process that generates energy for cells is particularly harmful to cells in the developing brain, and this impairment results in the signs and symptoms of fumarase deficiency.
This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition. However, people with one mutated copy of the FH gene in each cell, including parents of individuals with fumarase deficiency, tend to develop benign tumors containing smooth muscle tissue (leiomyomas) in the skin and, in females, the uterus. They also have an increased risk of kidney cancer. This condition is called hereditary leiomyomatosis and renal cell cancer (HLRCC).
This entry is adapted from the peer-reviewed paper https://medlineplus.gov/genetics/condition/fumarase-deficiency