Homocysteinuria

Types (all autosomal recessive):

  • Cystathionine beta synthase deficiency
    • Cannot convert homocysteine to cystathionine
      • Treatment: ↓ methionine, ↑ cysteine, ↑ B6, B12, and folate in diet)
  • Decreased affinity of cystathionine synthase for pyridoxal phosphate
  • See Metabolism (summary)
  • Methionine synthase (homocysteine methyltransferase) deficiency (treatment: ↑ methionine in diet)
  • Methylene tetrahydrofolate reductase deficiency – most common genetic cause of hyperhomocysteinemia.
  • May be precipitated by low cobalamin, pyridoxine and folate.
  • All forms result in excess homocysteine.
  • HOMOCYstinuria: ↑↑ Homocysteine in urine, Osteoporosis, Marfanoid habitus, Ocular changes (downward and inward lens subluxation), Cardiovascular effects (thrombosis and atherosclerosis → stroke and MI), kYphosis, intellectual disability. In homocysteinuria, lens subluxes “down and in” (vs Marfan, “up and fans out”).

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