Cloning and characterization of human FTCD on 21q22.3, a candidate gene for glutamate formiminotransferase deficiency.

We have identified a new human gene, FTCD, which maps to chromosome 21q22.3 and encodes the enzyme formiminotransferase cyclodeaminase, an intermediate metabolism enzyme that links histidine catabolism to folate metabolism. The major cDNA encodes a protein containing 541 amino acid residues and shows 84% identity with porcine FTCD. Several other cDNAs have been isolated, which may result from alternative splicing events and have the potential to code for three different protein isoforms. The gene is highly expressed in human fetal and adult liver. The two FTCD protein domains show high sequence similarity to two distinct open reading frames from eubacterial genomes, suggesting that eukaryotic FTCD appeared through a gene fusion event. Defects in the glutamate formiminotransferase pathway have been documented, and the deficiency is presumed to be inherited as an autosomal recessive trait. The sequence reported here may be helpful in identifying the primary defect in glutamate formiminotransferase deficiency and establishing a molecular diagnosis.