SLC7A7 encodes the y+L amino acid transporter 1 (y+LAT1). As a heterodimer with SLC3A2 in the plasma membrane, SLC7A7 mediates the exchange of arginine (L-Arg) for leucine (L-Leu) and a sodium ion (Na+). The physiological concentrations of arginine and leucine are expected to favor arginine export (Schweikhard & Ziegler 2012). Defects in SLC7A7 can cause Lysinuric protein intolerance (LPI; MIM:222700), a metabolic disorder characterised by decreased cationic amino acid (CAA) transport at the basolateral membrane of epithelial cells in the intestine and kidney, increased renal excretion of CAA and orotic aciduria. There is extreme variability clinically but typical symptoms include refusal to feed, vomiting and consequent failure to thrive. Hepatosplenomegaly, hematological anomalies and neurological involvement are recurrent clinical features (Sperandeo et al. 2008, Sebastio et al. 2011).