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