Metabolic Disorders

Metabolic Disorders

Inborn Errors of Metabolism

Shari Simone


  • 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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