A 3 day child vomits everything he feeds, has a distened abdomen & diarrhoea. The urine is positive for benedicts test for reducing substance. The substance in urine is

Galactosemia caused by the deficiency of enzyme GALT(galactose-1-phosphate uridyl transferase).Patients appear normal at bih,but by 3-4 days of breast milk,/formula feeding,show life threatening disease with vomiting,diarrhoea,poor weight gain,hepatic and renal manifestations and cataract.In case if suspected galactosemia,the urine should be tested simultaneously with Benedict reagent and by glucose-oxidase method.A negative dipstick by glucose oxidase method with positive Benedict reaction indicates nonglucose reducing substances,like galactose. Reference:Essential pediatrics-Ghai,8th edition,page no:657.