Lysinuric protein intolerance (LPI)
- Solute carrier family 7 member 7 (SLC7A7)
LPI is an autosomally recessively inherited amino acid disorder caused by defective transport of cationic amino acids lysine, arginine and ornithine in the intestine and kidney tubules. The transport protein y+LAT-1, encoded by the gene SLC7A7 at chromosome 14q11-13 directs the absorption of lysine at the basolateral membrane of intestinal epithelial cells and the reabsorption in the tubular cells of the kidney. The absence or dysfunction of the transport process leads to low plasma and high urine concentration of the cationic (dibasic) amino acids. Clinical presentation of the disease varies greatly, usually taking place during the weaning period, when breast feeding is replaced by cows milk and other high protein diets. Nausea, vomiting and mild diarrhea usually are the first symptoms followed by failure to thrive and growth retardation. Later liver and spleen become enlarged, muscles are hypotonic and osteoporosis can cause bone fractures. High protein intake can lead to hyperammonemia and even to coma, possibly accounting for the mild intellectual deficit found in few cases of LPI. Many patients have spontaneously developed aversion to protein rich food. A pulmonary complication of unknown mechanism, alveolar proteinosis has occurred in few patients during adulthood with fatal outcome. No specific cure is available, but with protein restriction and citrulline suplementation amino acid metabolism can be controlled and the patients are capable of a near normal life. Diagnosis of LPI is based on amino acid assays in plasma and urine. A gene test for the founder mutation is available to confirm the diagnosis.
UMLS Concept names
- Torrents D, Mykkänen J, Pineda M, FeliubadalÃ³ L, EstÃ©vez R, de Cid R, Sanjurjo P, Zorzano A, Nunes V, Huoponen K, Reinikainen A, Simell O, Savontaus ML, Aula P, PalacÃn M. Identification of SLC7A7, encoding y+LAT-1, as the lysinuric protein intolerance gene. Nat Genet. 1999 Mar;21(3):293-6. (Pubmed)