Lysinuric protein intolerance (LPI) is a very rare multisystem disease caused by abnormalities in the metabolism of the amino acids lysine, arginine, and ornithine. Patients with LPI have features associated with protein intolerance, bone marrow abnormalities, altered immune response, osteopenia, intellectual disability, chronic renal disease, and lung involvement. Diagnosis is based on the concentration of lysine, arginine, and ornithine in plasma and urine; increased urinary excretion and low plasma concentrations indicate a positive diagnosis for LPI.
Mutations in the SLC7A7 gene have been identified in patients with LPI. SLC7A7 gene encodes the lighter protein subunit of a sodium-independent cationic amino acid transporter, which is involved in the transport of certain amino acids between cells. Mutations in SLC7A7 gene impair the transport of lysine, arginine, and ornithine amino acids, and increase the excretion of these amino acids through urine.