Lactose intolerance and lactase genotype
Lactose intolerance occurs when the enzyme lactase, which breaks down lactose into glucose and galactose, is reduced in the small intestine. When lactose is not digested properly, it is transported further to the large intestine, where it is fermented by intestinal bacteria. This process can lead to gas, bloating, osmotic diarrhea and stomach discomfort, often within a few hours of consuming dairy products.
Lactase deficiency can be primary (genetically determined) or secondary, which means that lactase production is temporarily or permanently reduced due to damage to the intestinal mucosa. Secondary lactase deficiency can occur in celiac disease, intestinal infections, inflammatory bowel diseases or after intestinal surgery. Primary lactose intolerance is hereditary and is most common in populations where lactase production is naturally downregulated in adulthood, while secondary lactose intolerance can be transient if the underlying cause is treated.
What is lactose?
Lactose is a disaccharide consisting of glucose and galactose and is the primary milk sugar in dairy products. In order to be absorbed in the small intestine, lactose must be broken down by the enzyme lactase, which allows its components to be absorbed as an energy source. Lactose is particularly important during infancy but has a reduced biological importance in adulthood in many populations.
What is lactase?
Lactase is an enzyme produced in the mucosa of the small intestine and catalyzes the breakdown of lactose. Genetic regulation determines the production of lactase, which varies between individuals and ethnic groups. In most infants, lactase activity is high, but in some adults there is a gradual downregulation, which can lead to lactose intolerance.
Indication for testing for lactose intolerance
In cases of suspicion of lactose intolerance, it is recommended to first eliminate lactose followed by provocation to see if symptoms occur. Genotyping of the lactase gene (LCT-13910 C/T) may be justified in cases where uncertainty remains or where there is a need to determine a genetic predisposition.
Genotype and interpretation of lactose intolerance test
Primary lactose intolerance is linked to genetic variants at position 13910 upstream of the lactase gene (LCT).
LCTg.-13910 C/C (homozygous), Primary lactose intolerance- Lactase production gradually decreases after childhood, and symptoms occur when lactose is ingested.
- Common in many parts of the world (90-100% in some regions of Africa and Asia), but occurs in a few percent of Swedes.
- Individuals usually tolerate lactose, but some may develop milder symptoms in adulthood.
- Continued lactase production throughout life.
Individuals with the C/C genotype have normal lactase activity as infants, but a downregulation occurs gradually, leading to manifest lactose intolerance in adolescence or adulthood. Children with this genotype therefore often do not show symptoms early in life.
Limitations and population-specific interpretation
The test is validated primarily in European populations, where the C/C genotype strongly correlates with lactose intolerance. In some cases, individuals of non-European origin and the C/C genotype may still have preserved lactase production due to mutations in other regions of the lactase gene.
Summary
Blood test for the B-Lactase gene genotype analyzes the LCT-13910 C/T polymorphism and can be used to determine genetic predisposition for primary lactose intolerance. However, the test cannot diagnose secondary lactose intolerance, and clinical assessment should always include dietary testing (elimination/provocation) if intolerance is suspected.