A newborn baby refuses breast milk since the 2nd day of bih but accepts glucose-water, develops vomiting and severe jaundice by the 5th day. Benedict's test was positive for urine and blood glucose was low. The most likely cause is due to the deficiency of

The above clinical features suggest a disorder of galactose metabolism. Galactose-1-phosphate uridyl transferase deficiency leads to classical galactosemia. It is an autosomal recessive disorder. Clinical features : Accumulation of galactose-1-phosphate in the liver causes liver damage & leads to hepatomegaly, vomiting, convulsions. Accumulation of galactose-1-phosphate depletes the liver of inorganic phosphate leading to diminished ATP synthesis which affects gluconeogenesis resulting in hypoglycemia. Accumulation of galactose-1-phosphate in the nerves causes intellectual disability. Accumulation of galactitol in the lens causes oil-drop cataract. Urinary reducing sugar (Benedict's test) and Mucic acid test is positive. Treatment is galactose-free diet. Reference: Lippincott's Illustrated biochemisty 6th Edition Pg 141