: A rare inborn urea cycle disorder characterized by an enzyme defect in the amino acid transporter gene SLC7A7 (positive amino acid transporter).
* Pulmonary alveolar proteinosis * Glomerulonephritis * Osteoporosis * Immune deficiency
It has been associated with SLC7A7.
The diagnosis is based on the biochemical findings (increased concentrations of lysine, arginine and ornithine in urine and low concentrations of these amino acids in plasma, elevation of urinary orotic acid excretion after protein-rich meals, and inappropriately high concentrations of serum ferritin and lactate dehydrogenase isoenzymes) and the screening of known mutations of the causative gene from a DNA sample.
Under proper dietary control and supplementation, the majority of the LPI patients are able to have a nearly normal life.
Treatment of LPI consists of protein-restricted diet and supplementation with oral citrulline. Citrulline is a neutral amino acid that improves the function of the urea cycle and allows sufficient protein intake without hyperammonemia.