Lactose intolerance, the inability to digest lactose, results from a deficiency of the enzyme lactase, leading to gastrointestinal issues after consuming dairy. While not typically life-threatening, it can cause significant discomfort. The incidence of lactose intolerance varies by race, with higher rates among Native Americans, Blacks, Latinos, Asians, Mediterraneans, and Jews (75-90%) compared to those of Northern and Central European descent (5%). This difference is attributed to a genetic mutation causing lactase persistence.
Are There Genetic Factors That Influence Lactose Intolerance?
Yes, genetic factors significantly influence lactose intolerance. Primary lactose intolerance, the most common type, is often due to a genetically determined decline in lactase production after weaning. This decline is normal in most mammals, but a genetic mutation allows some populations, particularly those of Northern European descent, to maintain lactase production into adulthood, known as lactase persistence. This mutation is a dominant trait, meaning only one copy of the gene is needed to confer lactose tolerance.
What Specific Genes Are Involved in Lactose Intolerance?
The primary gene associated with lactase persistence is LCT, which encodes the lactase enzyme. Variations near this gene, particularly a single nucleotide polymorphism (SNP) called -13910*T, are strongly associated with the ability to digest lactose into adulthood. Individuals with the -13910*T allele continue to produce lactase, while those without it typically experience a decline in lactase production after childhood.
How Does Genetics Explain Differences in Lactose Intolerance Among Ethnic Groups?
The prevalence of the lactase persistence allele varies significantly across different ethnic groups. It is most common in populations with a long history of dairy farming, such as those of Northern European descent. In these populations, the ability to digest lactose provided a nutritional advantage, leading to the selection and spread of the lactase persistence allele. Conversely, in populations without a history of dairy farming, the lactase persistence allele is less common, resulting in higher rates of lactose intolerance.
Can Lactose Intolerance Be Congenital?
Yes, congenital lactose intolerance exists, although it is rare. This condition is present from birth and is caused by a different genetic defect than primary lactose intolerance. Congenital lactose intolerance is typically caused by mutations in the LCT gene that result in a complete absence of lactase production. Infants with this condition cannot digest lactose in breast milk or formula and require lactose-free alternatives from birth.
What Other Factors Can Cause Lactose Intolerance?
Besides genetic factors, secondary lactose intolerance can develop due to damage to the small intestine. This damage can be caused by infections (such as rotavirus or giardia), inflammatory bowel disease, celiac disease, cystic fibrosis, or other conditions that injure the intestinal lining. Medical treatments like chemotherapy, radiation, and bowel surgery can also lead to secondary lactose intolerance. In these cases, lactose intolerance may be temporary and improve as the intestinal lining heals.
Are There Any Genetic Factors That Influence Colic?
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