In this video the biochemical mechanism for the presence of jaundice in classic galactosemia is explained. Classic galactosemia is due to defect in galactose 1-phosphate uridyltransferase enzyme. this leads to elevation of galactose 1-phosphate thereby trapping the inorganic phosphate which can lead to fasting hyperglycemia, mental retardation. Elevated galactose 1-phosphate acts negatively on phosphoglucomutase enzyme and decrease the availability of glucose 1-phosphate leading to decreased UDP-glucose and consequently decreased UDP-glucoronate. Decreased availability of UDP-glucoronate lead to decreased activity of UGT1A1. Decreased activity of UGT1A1 lead to decreased conjugation of bilirubin and hence elevated levels of unconjugated bilirubin leading to jaundice. bilateral cataract seen in classic galactosemia is due to increased galactitol formation.
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