Tyrosinemia Enzymes : Mnemonic

Mnemonic:ย FAHeem TATtooes because of Histrionic Personality Disorder (HPD)

Tyrosine is necessary for biosynthesis of catecholamines, thyroid hormones and melanin pigment.


1. Tyrosinemia type I (Tyrosinosis/Hepatorenal tyrosinemia):

  • Enzyme defect: FAH (Fumaryl-acetoacetate hydroxylase)
  • Last enzyme in the cycle
  • Cabbage like odor
  • Hepatocellular carcinoma
  • Renal tubular acidosis
  • Peripheral neuropathy

2. Tyrosinemia type II (Oculo-cutaneous/Richner-Hanhart):

  • Enzyme defect: TAT (Tyrosine Amido-Transferase)
  • 1st enzyme in the cycle (hepatic enzyme)
  • Corneal erosions
  • Palmoplantar keratosis
  • Mental retardation

3. Tyrosinemia type III (Neonatal):

  • Enzyme defect: HPD (Hydroxy-Phenylpyruvate-Dioxygenase)
  • Second enzyme in the cycle
  • Neurologic dysfunction


Alkaptonuria: Mnemonic – HAO

  • Enzyme defect: HAO (Homogentisic Acid Oxidase)
  • Clinical features:
    • Homogentisic aciduria (urine turns black on standing; Benedict’s/FeCl3 test positive)
    • Arthritis (large joints; narrowing of joint space and calcification of IV disc)
    • Ochronosis (darkening of sclera, ear and nose cartilage, tympanic membrane, palmoplantar skin, large joints and IV disc due to deposition of benzoquinone acetate, i.e. oxidized homogentisic acid)

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