Aminoacidopathies

Investigations

• Amino acid profile (plasma or urine), e.g. PKU-phenylalanine increases
• Enzyme or molecule test confirmation may be necessary

Management

• Very low protein diet
• Specialized medications
• Supplementary specialized formula (vitamins, minerals, carbohydrates, and all essential amino acids expert one[s] the patient cannot metabolize to make a complete diet), e.g. for PKU, low-phenylalanine diet for life (some phenylalanine must be given as this amino acid is not synthesized in the body). During pregnancy, the diet must be strictly adhered to because high phenylalanine levels result in fetal abnormalities, e.g. CHD, and mental retardation.

Phenylketonuria

• The most common metabolic disorder: incidence 1 in 15000
• Phenylketonuria (PKU) is caused by a defect in the breakdown of phenylalanine. The enzyme phenylalanine hydroxylase is low or absent and phenylalanine and its alternative pathway metabolites accumulate in the tissues.
  
  
  

Clinical features:

These only develop if the condition is untreated:

• Slowly progressive mental retardation
• Spastic cerebral palsy, athetosis, hyperactivity, acquired microcephaly
• Fair hair and skin, blue eyes

Neonatal screening is well established for PKU (Guthrie test - phenylalanine levels increases) and the classical phenotype is now rarely seen.

Maple syrup urine disease

This is an inability to break down the branched-chain amino acids isoleucine, leucine, and valine. It usually presents in the neonatal period with encephalopathy.

Tyrosinaemia

This presents with acute or chronic liver disease and renal disease with renal rickets.