Glutamate formiminotransferase deficiency is a rare disorder; approximately 20 affected individuals have been identified. Of these, about one-quarter have the severe form of the disorder. Everyone reported with the severe form has been of Japanese origin. The remaining individuals, who come from a variety of ethnic backgrounds, are affected by the mild form of the condition.

Mutations in the FTCD gene cause glutamate formiminotransferase deficiency. The FTCD gene provides instructions for making the enzyme formiminotransferase cyclodeaminase. This enzyme is involved in the last two steps in the breakdown (metabolism) of the amino acid histidine, a building block of most proteins. It also plays a role in producing one of several forms of the vitamin folate, which has many important functions in the body.

FTCD gene mutations that cause glutamate formiminotransferase deficiency reduce or eliminate the function of the enzyme. It is unclear how these changes are related to the specific health problems associated with the mild and severe forms of glutamate formiminotransferase deficiency, or why individuals are affected by one form or the other.