A one year old child was detected with a reducing sugar in urine.Glucose oxidase test and seliwanoff's test were negative.What is the sugar likely to be?

The child is likely to have galactosemia which results in galactosuria.Inability to metabolize galactose occurs in the galactosemias, which may be caused by inherited defects of galactokinase, uridyl transferase, or 4-epimerase, though deficiency of uridyl transferase is best known.The condition is more severe if it is the result of a defect in the uridyl transferase since galactose 1-phosphate accumulates and depletes the liver of inorganic phosphate. Ultimately, liver failure and mental deterioration result. Glucose oxidase test is specific for glucose and seliwanoff's test for fructose.Lactosuria occurs in pregnancy and lactation when lactose is synthesized in the body. Ref: Bender D.A., Mayes P.A. (2011). Chapter 21. The Pentose Phosphate Pathway & Other Pathways of Hexose Metabolism. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper's Illustrated Biochemistry, 29e.