Editorial Focus Lysinuric protein intolerance: one gene, many problems

AMINO ACIDS are efficiently absorbed in intestine and kidney by epithelial cells endowed with transporters for specific groups of amino acids. Inherited renal aminoacidurias arise as a result of mutations inactivating apical or basolateral transport systems. Although aminoacidurias are diagnosed by urine amino acid analysis, most of the disorders affect both intestinal and renal transport. In the intestine, peptide transporters and amino acid transporters work in parallel in the apical membrane to aid in protein absorption. Mutations in apical transporters, as a result, show predominantly renal phenotypes because intestinal mal-absorption is compensated by peptide transport (5). Lysinuric protein intolerance (LPI), by contrast, is an autosomal reces-sive disorder affecting the basolateral transporter for cationic amino acids in the kidney and intestine (12). It is generally assumed that a block of basolateral membrane transport i