<prompt> A two year old child presents with persistent diarrhaea acidic stools and presence of one per cent of reducing substance in the fresh stools. What is the most probable diagnosis ?Cystic fibrosisLactose intoleranceRotavirus induced diarrhoeaIntestinal tuberculosis  <response>: DISACCHARIDASES DEFECIENCY Lactase defeciency diagnosis based on presence of more than .5of reducing substance in the fresh stools acidic stools abnormal oral sugar tolerance test breath Hydrogen excretion of more than 11ppm following a loading dose of lactose enzyme assay on mucosal biopsies showing low levels of disaccharidases Ref : ESSENTIAL PEDIATRICS,O.P.GHAI,PG NO:274, 7th edition 