GTR Home > Conditions/Phenotypes > Hyperlysinemia


Hyperlysinemia type I is an autosomal recessive metabolic condition with variable clinical features. Some patients who present in infancy with nonspecific seizures, hypotonia, or mildly delayed psychomotor development have been found to have increased serum lysine and pipecolic acid on laboratory analysis. However, about 50% of probands are reported to be asymptomatic, and hyperlysinemia is generally considered to be a benign metabolic variant (summary by Tondo et al., 2013; Houten et al., 2013). The AASS gene encodes a bifunctional enzyme: lysine alpha-ketoglutarate reductase and saccharopine dehydrogenase. In hyperlysinemia type I, both enzymatic functions of AASS are defective; in hyperlysinemia type II, also known as saccharopinuria (268700), some of the first enzymatic function is retained (Cox, 1985; Cox et al., 1985). [from OMIM]

Available tests

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Associated genes

Clinical features

  • Anemia
  • Short attention span
  • Intellectual disability
  • Cognitive impairment
  • Seizure
  • Abnormality of the genitourinary system
  • Delayed speech and language development
  • Hyperactivity
  • Ectopia lentis
  • Muscular hypotonia
  • Hyperlysinemia
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