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Inherited Metabolic Disorders

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Types of Inherited Metabolic Disorders

Hundreds of inherited metabolic disorders have been identified, and new ones continue to be discovered. Some of the more common and important genetic metabolic disorders include:

Lysosomal storage disorders : Lysosomes are spaces inside cells that break down waste products of metabolism. Various enzyme deficiencies inside lysosomes can result in buildup of toxic substances, causing metabolic disorders including:

  • Hurler syndrome (abnormal bone structure and developmental delay)
  • Niemann-Pick disease (babies develop liver enlargement, difficulty feeding, and nerve damage)
  • Tay-Sachs disease (progressive weakness in a months-old child, progressing to severe nerve damage; the child usually lives only until age 4 or 5)
  • Gaucher disease (bone pain, enlarged liver, and low platelet counts, often mild, in children or adults)
  • Fabry disease (pain in the extremities in childhood, with kidney and heart disease and strokes in adulthood; only males are affected)
  • Krabbe disease (progressive nerve damage, developmental delay in young children; occasionally adults are affected)

Galactosemia: Impaired breakdown of the sugar galactose leads to jaundice, vomiting, and liver enlargement after breast or formula feeding by a newborn.

Maple syrup urine disease: Deficiency of an enzyme called BCKD causes buildup of amino acids in the body. Nerve damage results, and the urine smells like syrup.

Phenylketonuria (PKU): Deficiency of the enzyme PAH results in high levels of phenylalanine in the blood. Mental retardation results if the condition is not recognized.

Glycogen storage diseases: Problems with sugar storage lead to low blood sugar levels, muscle pain, and weakness.

Mitochondrial disorders: Problems inside mitochondria, the powerhouses of cells, lead to muscle damage.

Friedreich ataxia: Problems related to a protein called frataxin cause nerve damage and often heart problems. Inability to walk usually results by young adulthood.

Peroxisomal disorders: Similar to lysosomes, peroxisomes are tiny spaces filled with enzymes inside cells. Poor enzyme function inside peroxisomes can lead to buildup of toxic products of metabolism. Peroxisomal disorders include:

  • Zellweger syndrome (abnormal facial features, enlarged liver, and nerve damage in infants)
  • Adrenoleukodystrophy (symptoms of nerve damage can develop in childhood or early adulthood depending on the form.)

Metal metabolism disorders: Levels of trace metals in the blood are controlled by special proteins. Inherited metabolic disorders can result in protein malfunction and toxic accumulation of metal in the body:

  • Wilson disease (toxic copper levels accumulate in the liver, brain, and other organs)
  • Hemochromatosis (the intestines absorb excessive iron, which builds up in the liver, pancreas, joints, and heart, causing damage)

Organic acidemias: methylmalonic acidemia and propionic acidemia.

Urea cycle disorders: ornithine transcarbamylase deficiency and citrullinemia

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