Intestinal folate transporter method

A method of diagnosing folate malabsorption in a human or determining whether a human may be a carrier of a nucleic acid associated with folate malabsorption, said method comprising

• (i) determining whether or not the human has a mutation in one or both copies of nucleic acid encoding proton-coupled folate transporter (PCFT), in comparison to a wild type PCFT nucleic acid, resulting in a loss of PCFT function or reduced PCFT activity, wherein a mutation in both copies of the nucleic acid encoding PCFT resulting in loss of PCFT function or reduced PCFT activity is diagnostic of folate malabsorption and a mutation in one copy of the nucleic acid encoding PCFT is indicative that the human may be a carrier of a gene associated with folate malaborption, wherein the wild type PCFT nucleic acid encodes the amino acid sequence of SEQ ID NO:2, wherein the mutation is selected from 5882G>A of SEQ ID NO:6, 2284delG of SEQ ID NO:6, 2844C>A of SEQ ID NO:6, 2946G>C of SEQ ID NO:6, 3461C>G of SEQ ID NO:6, 5927C>T of SEQ ID NO:6 or 7548C>G of SEQ ID NO:6;
• or
• (ii) determining whether or not the human expresses an active PCFT, wherein an active PCFT is indicative that the human has the ability to undergo intestinal folate absorption and the absence of an active PCFT is diagnostic of folate malabsorption, wherein the active PCFT has the amino acid sequence of SEQ ID NO:2.