Les intolérances héréditaires aux disaccharides ou aux oses simples

Hereditary sugar intolerances essentially concern the metabolism of the two main disaccharides of our feeding, i.e. saccharose (or sucrose) and lactose. When the defecting enzyme is that which hydrolyses the disaccharide allowing the intestinal ingestion of simple oses, symptoms are mainly digestive with an osmotic diarrhoea as soon as the sugar is introduced in the diet. Most often, the diagnosis will be simply clinically, but biology can establish the diagnosis in borderline cases and in adults with biochemical analysis of the defecting tissue and sometimes with genetic analysis since we can characterize some mutations responsible for deleterious phenotypes. This diagnosis is important since it will impose specific sugar restriction, energetic replacement, and an eventual oral substitutive therapy. Lactose intolerance is more serious than saccharose intolerance. The intolerances for simple oses, fructose and galactose, are even more serious because the deficient enzymes concern the hepatic metabolism of these sugars. Symptoms are both digestive and hepatic, often with renal impairment, for example with Fanconi syndrome. Sometimes only liver transplantation will be able to save the child. Specific sugar restriction is indispensable. The biochemical diagnosis is always necessary; it can be done on liver biopsy for fructose intolerance, or on a blood sample for galactosemia. Genetic is more and more important for diagnosis, neonatal screening, and allows to improve nosology.