Identification of SLC7A7, encoding y(+)LAT-1, as the lysinuric protein intolerance gene

Lysinuric protein intolerance (LPI; OMIM 222700) is a rare, recessive disor der with a worldwide distribution, but with a high prevalence in the Finnis h population(1); symptoms include failure to thrive, growth retardation, mu scle hypotonia and hepatosplenomegaly. A defect in the plasma membrane tran sport of dibasic amino acids has been demonstrated at the basolateral membr ane of epithelial cells in small intestine and in renal tubules(2-4) and in plasma membrane of cultured skin fibroblasts(5) from LPI patients. The gen e causing LPI has been assigned by linkage analysis to 14q11-13. Here we re port mutations in SLC7A7 cDNA (encoding y(+)L amino acid transporter-1, y()LAT-1), which expresses dibasic amino-acid transport activity and is locat ed in the LPI region, in 31 Finnish LPI patients and 1 Spanish patient. The Finnish patients are homozygous for a founder missense mutation leading to a premature stop codon. The Spanish patient is a compound heterozygote wit h a missense mutation in one allele and a frameshift mutation in the other. The frameshift mutation generates a premature stop codon, eliminating the last one-third of the protein. The missense mutation abolishes y(+)LAT-1 am ino-acid transport activity when co-expressed with the heavy chain of the c ell-surface antigen 4F2 (4F2hc, also known as CD98) in Xenopus laevis oocyt es. Our data establish that mutations in SLC7A7 cause LPI.