|Fumarate is broken down by fumarase|
Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
Fumarase deficiency is an enzyme irregularity that causes severe mental retardation, unusual facial features, brain malformation, and epileptic seizures due to an abnormally low amount of fumarase in cells. The condition is congenital and is the result of receiving two defective recessive genes on the first chromosome that influence the functioning of the Krebs Cycle.
Fumarase deficiency is extremely rare. Until a few years ago scientists knew of only thirteen cases worldwide. However, recently twenty additional cases have been documented in the border towns of Colorado City, Arizona, and Hildale, Utah. These two towns constitute a closed and controlled community, and were settled in the 1930s by the Fundamentalist Church of Jesus Christ of Latter Day Saints, which is a breakaway sect of The Church of Jesus Christ of Latter-day Saints. As such, many of the surrounding communities refer to this disease as "Polygamist's Down's"
The fumarase deficiency gene has become very common in this community, due to the practice of inbreeding. It is believed that either Joseph Smith Jessop or one of the founders of the communities, or his wife carried the gene and passed it on to their descendants.
The populations of Colorado City and Hildale are examples of the founder effect.
Signs and symptoms
- Ammonia levels raised (blood)
- Organic aciduria
- Corpus callosum hypoplasia
- Learning disability
- U.S. polygamist community faces rare genetic disorder, June 14, 2007, Reuters
- Deseret Morning News article from February 9, 2006, about Fumarase Deficiency in Hildale, Utah, and Colorado City, Arizona.
- Phoenix New Times article from December 29, 2005, about Fumarase Deficiency in Hildale, Utah, and Colorado City, Arizona.