Supplementary Material for: Lysinuric Protein Intolerance: not only a disorder for pediatric nephrologists. Case report.

Introduction. Lysinuric Protein Intolerance (LPI) is a multisystemic inborn error of metabolism with a variable clinical expressivity, that usually begins in childhood with growth failure and gastroenterological/neurological problems related to the altered urea cycle and later complications involving the renal, pulmonary and immuno-hematological systems.
Case report: We present the case of a 40-year-old woman suffering from chronic kidney disease in the context of a LPI, whose diagnosis was challenging because the signs of the disease were always blurred and the patient never manifested critical episodes typical of this multisystemic disease. In addition to renal disease, splenomegaly, thrombocytopenia, elevated lactate dehydrogenase (LDH), hyperferritinemia and hypertriglyceridemia were also present. A thorough investigation of the patient’s food preferences revealed her spontaneous aversion to protein-containing foods and excessive drowsiness during the occurrence of infectious episodes or on the rare occasions of excessive protein intake, although without ever coming to medical attention. These nuanced signs led us to suspect an impairment of the urea cycle and ultimately allowed us to narrow down the diagnosis to LPI through biochemical and genetic investigations.
Conclusion. Nephrologists should consider LPI in the differential diagnosis, whenever a patient presents with mixed proteinuria, tubular dysfunction and/or chronic kidney failure of unknown origin. In these circumstances, we suggest looking for other signs such as growth failure, signs and symptoms ascribed to urea-cycle impairment, pulmonary involvement, hepatosplenomegaly and laboratory alterations such as pancytopenia, hyperferritinemia, lipid abnormalities, elevated LDH.