Metabolic Disorders

Metabolic Disorders
Inborn Errors of Metabolism
Shari Simone
Background
  • Genetic metabolic disorders, also known as inborn errors of metabolism (IEM), are individually rare, but collectively numerous and occur in 1 of 1,500 children.
  • Most metabolic disorders are inherited as autosomal recessive traits.
General Classification
  • Disorders of protein metabolism.
    • Amino acid disorders (e.g., phenylketonuria or PKU).
    • Organic acid disorders (e.g., propionic acidemia).
    • Urea cycle disorders (e.g., ornithine transcarbamylase (OTC) deficiency).
  • Disorders of glucose metabolism.
    • Glycogen storage disease (GSD) (e.g., Pompe disease).
    • Other carbohydrate disorders (e.g., galactosemia).
  • Disorders of fat metabolism.
    • Fatty acid oxidation disorders (e.g., medium-chain acyl-CoA dehydrogenase (MCAD) deficiency).
  • Disorders of organelles.
    • Mitochondrial disorders (e.g., Leigh syndrome).
    • Lysosomal storage disorders (e.g., mucopolysaccharidosis such as Hurler syndrome, sphingolipidoses such as Tay-Sachs disease).
    • Peroxisomal disorders (e.g., Zellweger syndrome).
  • Other disorders: purine and pyrimidine disorders, porphyrias, metal disorders (e.g., Wilson disease).
    • These disorders are extremely rare and only Wilson disease will be discussed.
Specific Metabolic Disorders
Disorders of Protein Metabolism
  • Amino acid disorders.
    • Pathophysiology.
      • A defect in the metabolic pathways of amino acids resulting in abnormal accumulation of amino acids in the plasma.
      • Examples: PKU, nonketotic hyperglycinemia.
    • Clinical presentation.
      • Often presents in newborns who may initially be well and then become acutely symptomatic.
      • May experience metabolic decompensation with poor feeding and lethargy after a period of protein feeding.
      • Symptoms in newborn range from none to metabolic acidosis, hyperammonemia, hypoglycemia, ketosis, and liver dysfunction.
      • May progress to encephalopathy, coma, or death if not recognized.
    • Diagnostic evaluation.
      • Quantitative plasma amino acids and qualitative urine organic acids.
      • Specific enzyme analysis.
    • Management.
      • Complete protein restriction initially, then change to amino acid-restricted diet (i.e., phenylalanine-restricted diet) when specific amino acid disorder identified.
      • Infants and children should be monitored regularly during the developmental period.
      • Strict dietary therapy is recommended to be continued for life for some disorders (i.e., maple syrup urine disease).
  • Urea cycle disorders.
Jan 30, 2021 | Posted by in NURSING | Comments Off on Metabolic Disorders

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