Lactose intolerance is a common condition where the body reacts adversely to milk sugar due to decreased lactase activity in the small intestine's epithelium. This condition is not to be confused with cow's milk allergy, which involves the immune system's response to milk protein.
Symptoms of lactose intolerance may vary from one individual to another and can appear immediately or a few hours after consuming milk, milk products, or foods containing lactose. Some common symptoms include stomach pain, nausea, diarrhea, and gas, and their intensity can vary.
Lactase-phlorizin hydrolase (LPH) is an enzyme responsible for lactose digestion. The LPH enzyme is encoded by the lactase gene (LCT) and expressed in the small intestine. Studies have shown that lactose intolerance may be due to genetic factors, as the ability to digest lactose is a trait that follows a dominant inheritance pattern. This trait is especially common among descendants of populations that have traditionally practiced cattle domestication.
The decline in lactase levels over time is a natural process, but the exact reason for this decline is not yet known. Two genetic variants have been identified that are related to the expression of the LPH enzyme and its production in adulthood. These variants are not located within the LCT gene but within a regulatory region called MCM6 that modulates LCT expression.
Some variants in the MCM6 gene can lead to decreased LCT expression in intestinal cells, which over time can eventually lead to lactose intolerance and discomfort when lactose is consumed in certain amounts.
It is important to differentiate a person with reduced LPH enzyme activity from other conditions such as congenital lactase deficiency and secondary hypolactasia. Congenital lactase deficiency is rare and occurs at the onset of lactation, caused by severe mutations in both alleles of the LCT gene. Secondary hypolactasia is caused by direct damage to the intestinal mucosa, resulting in a transient reduction of lactase activity, and has no genetic basis.
TellmeGen is a genetic testing service that can help identify genetic variants associated with lactose intolerance. This service can provide insight into how an individual's genes may affect their ability to digest lactose and inform them of potential lactose intolerance. However, it is essential to note that genetic testing alone cannot provide a definitive diagnosis of lactose intolerance, and consultation with a healthcare professional is necessary for proper diagnosis and treatment.