Updated: 2/1/2021

Galactose Metabolism

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Snapshot
  • A 2-week-old boy is brought to the emergency department after progressive lethargy over the course of the previous week. His parents report extended episodes of vomiting after feeding ever since birth though this has not previously been extensively investigated. Physical exam shows the development of bilateral cataracts so based on clinical suspicion a metabolic panel is conducted in order to evaluate for disorders of galactose metabolism.
Overview
  • Source
    • lactose in dairy products
      • disaccharide composed of glucose and galactose
      • hydrolyzed by lactase in brush border of small intestine
  • Metabolic pathway
    • trapped in cell by galactokinase
    • converted into glucose-1-phosphate through UDP mediated epimerization
    • glucose-1-phosphate can then be used
      • directly in glycogenesis
      • converted to glucose-6-phosphate and used in glycolysis
      • released as free glucose in hepatocytes
Pathophysiology
  • Galactokinase deficiency
    • presentation 
      • galactosemia/galactosuria
      • cataracts in childhood
      • excess galactose is converted to galactitol
      • catalyzed by aldose reductase
      • galactitol is osmotically active
    • treatment
      • galactose free diet
  • Gal-1-P uridyl transferase deficiency
    • similar to galactokinase deficiency but more severe
      • Gal-1-P acts as a phosphate sink
    • presentation 
      • early cataracts
      • more severe, with vomiting/diarrhea after milk ingestion
      • liver disease
      • lethargy
      • mental retardation
      • hepatomegaly
      • hyperbilirubinemia
        • jaundice
    • treatment
      •  galactose free diet
  • Lactose intolerance
    • mechanism
      • lactase deficiency
        • primary
          • hereditary
            • ↑ frequency in african americans and asians
          • age-dependent
        • secondary
          • post-gastroenteritis
    • presentation
      • bloating, cramps, osmotic diarrhea
        • symptoms due to fermentation of indigestible lactose by intestinal bacteria 
        • leads to production of H2, CH4, organic acids
          • H2 used in diagnosis
          • detected on breath following oral lactose load
    • treatment
      • eliminate dairy from diet
      • take lactase pills when consuming dairy

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