Hyperlysinemia

Hyperlysinemia (also known as familial hyperlysinemia or lysine alpha-ketoglutarate reductase deficiency) is a rare autosomal recessive inborn error of lysine metabolism caused by deficiency of the enzyme alpha-aminoadipic semialdehyde synthase (AASS), which catalyzes the first two steps of lysine degradation. The condition is characterized by elevated levels of lysine in the blood and urine. It is classified under ICD-10 code E72.3 (disorders of lysine and hydroxylysine metabolism) and Orphanet code 2203. Historically, hyperlysinemia was associated with intellectual disability, seizures, and spasticity in early case reports. However, subsequent population studies and identification of affected but asymptomatic individuals have led to the current understanding that hyperlysinemia is likely a benign biochemical variant rather than a disease-causing condition. Many individuals identified through newborn screening or family studies have been found to be completely asymptomatic, and the neurological findings in earlier reports are now thought to have been coincidental or due to ascertainment bias. Because hyperlysinemia is now generally considered a benign metabolic trait, no specific treatment is typically recommended. Some earlier approaches included dietary lysine restriction, but this is no longer considered necessary in most cases. Genetic counseling may be offered to families, and monitoring may be considered on a case-by-case basis if any clinical concerns arise. The condition primarily affects lysine metabolism without consistent impact on other organ systems.

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