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Xu, C. Hyperlysinemia. Encyclopedia. Available online: (accessed on 04 December 2023).
Xu C. Hyperlysinemia. Encyclopedia. Available at: Accessed December 04, 2023.
Xu, Camila. "Hyperlysinemia" Encyclopedia, (accessed December 04, 2023).
Xu, C.(2020, December 23). Hyperlysinemia. In Encyclopedia.
Xu, Camila. "Hyperlysinemia." Encyclopedia. Web. 23 December, 2020.

Hyperlysinemia is an inherited condition characterized by elevated blood levels of the amino acid lysine, a building block of most proteins.

genetic conditions

1. Introduction

Hyperlysinemia is caused by the shortage (deficiency) of the enzyme that breaks down lysine. Hyperlysinemia typically causes no health problems, and most people with elevated lysine levels are unaware that they have this condition. Rarely, people with hyperlysinemia have intellectual disability or behavioral problems. It is not clear whether these problems are due to hyperlysinemia or another cause.

2. Frequency

The incidence of hyperlysinemia is unknown.

3. Causes

Mutations in the AASS gene cause hyperlysinemia. The AASS gene provides instructions for making an enzyme called aminoadipic semialdehyde synthase. This enzyme performs two functions in the breakdown of lysine. First, the enzyme breaks down lysine to a molecule called saccharopine. It then breaks down saccharopine to a molecule called alpha-aminoadipate semialdehyde.

Mutations in the AASS gene that impair the breakdown of lysine result in elevated levels of lysine in the blood and urine. These increased levels of lysine do not appear to have any negative effects on the body.

When mutations in the AASS gene impair the breakdown of saccharopine, this molecule builds up in blood and urine. This buildup is sometimes referred to as saccharopinuria, which is considered to be a variant of hyperlysinemia. It is unclear if saccharopinuria causes any symptoms.

4. Inheritance

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

5. Other Names for This Condition

  • alpha-aminoadipic semialdehyde deficiency disease

  • familial hyperlysinemia

  • lysine alpha-ketoglutarate reductase deficiency disease

  • saccharopine dehydrogenase deficiency disease

  • saccharopinuria


  1. Markovitz PJ, Chuang DT, Cox RP. Familial hyperlysinemias. Purification andcharacterization of the bifunctional aminoadipic semialdehyde synthase withlysine-ketoglutarate reductase and saccharopine dehydrogenase activities. J Biol Chem. 1984 Oct 10;259(19):11643-6.
  2. Sacksteder KA, Biery BJ, Morrell JC, Goodman BK, Geisbrecht BV, Cox RP, Gould SJ, Geraghty MT. Identification of the alpha-aminoadipic semialdehyde synthasegene, which is defective in familial hyperlysinemia. Am J Hum Genet. 2000Jun;66(6):1736-43.
  3. Saudubray JM, Rabier D. Biomarkers identified in inborn errors for lysine,arginine, and ornithine. J Nutr. 2007 Jun;137(6 Suppl 2):1669S-1672S. doi:10.1093/jn/137.6.1669S. Review.
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Update Date: 23 Dec 2020