Patients with lactose intolerance can not digest milk sugar and suffer after ingestion of milk-products from dyspepsia, nausia and bellyache. Further symptoms like vertigo, sleep disorders, akne or depressions can also be triggered by lactose intolerance. A Therapy for affected persons is very simple and can be done by lactose-free diet. In Germany, about 15 million people are affected from primary lactase deficiency.
The main reason for lactose intolerance is a genetically based deficiency of the enzyme lactase phlorizin hydrolase (LPH), which is responsible for the disassembly of milk sugar. This widely distributed genetic disorder is a T/C polymorphism located at position –13910 in the regulatory region of this gene. Person homozygous for C/C-genotype are consequently deficient for enzyme lactase and posses higher risk for lactose intolerance. These results are in excellent accordance with results obtained by the lactose hydrogen breath test for the diagnosis of lactase non-persistence. Nevertheless, not all C/C-carriers must show typical symptoms because a fall short of individual level is necessary.
Furthermore, in some cases lactose intolerance can be due to secondary causes like mal-resorption problems (e. g. Morbus Crohn patients), infections or chemotherapy.
In babyhood and infancy the lactase production is very high but it decreases with higher age resulting in manifestation of primary lactase deficiency. Also a North-/ South gradient is visible: In Scandinavia the homozygous C/C-constellation is very rare whereas in Germany prevalence is about 15-20%. In Southern European countries up to 30% of all adults carry the C-allels homozygous.
Patients suffering from lactose intolerance have also a higher risk for osteoporosis due to the reduced calcium-intake via milk products. In consequence, the C/C-genotype associated with primary lactose intolerance is a genetic risk factor for bone fractures for elderly people.