Hyperlysinuria is an inborn error of metabolism, characterized by high amounts of the amino acid lysine in the urine causing a heavy load on the renal tubules. This condition arises due to the deficiency of the aminoadipic semialdehyse synthase enzyme that is involved in the metabolism of lysine. Apart from the high levels of lysine in the urine, usually, no other clinical signs can be seen. Thus, the condition is a benign one, with no adverse physical or mental effects.