Hereditary disorders of intestinal transport.

Hereditary abnormalities of intestinal transport are rare conditions but are of disproportionate 
importance because of the information they give regarding the mechanisms of 
intestinal absorption in man. The main disability is usually diarrhoea, but 
there may be abnormalities from lack of absorption of an essential 
nutrient or occasionally from absorption of compounds in excess due to 
failure of a normal control mechanism. These diseases are experiments of 
nature which cannot be exactly simulated in the laboratory animal, and 
thus may on occasions give information unobtainable from other sources. Most 
often, however, they confirm that the mechanisms of absorption studied in 
detail in smaller mammals are probably applicable to man. In some 
of these diseases there is an associated defect of transport in 
the proximal renal tubules as well as in the gut. They 
furnish evidence, therefore, that transport processes are closely related in the 
gut and in the kidney, or at least that an important 
step in transport is identical at the two sites. Such disorders 
include disorders of carbohydrate absorption, hereditary defects of amino acid absorption, 
hereditary defects in the absorption of fat, hereditary disorders of the 
intestinal absorption of electrolytes, and hereditary defects of vitamin B12 absorption. 
