Lactose Intolerance

Lactose Intolerance

Lactose intolerance is a clinical syndrome characterized by the inability to digest lactose, the main carbohydrate in milk and dairy products. Statistically, this problem occurs in 60% of the world's population (around 28% in European populations and up to 70% in the Middle East).

The primary cause of lactose intolerance is reduced activity of lactase, an enzyme required for lactose hydrolysis into glucose and galactose. Lactase LCT gene expression is regulated by a promoter region located upstream of the gene from the start of lactase transcription in the intron of the neighboring MCM6 gene.

The -13910 T>C polymorphism in the MCM6 gene intron plays a key role in regulating lactase-encoding LCT gene activity and the development of primary lactase deficiency. This is the most prevalent form of this clinical syndrome. Unlike secondary lactase deficiency, which stems from intestinal diseases (such as celiac disease, inflammatory bowel disease or infectious enteritis), the primary form is solely due to a genetically determined decrease in lactase activity. In European populations, the most common polymorphism is the -13910 C>T polymorphism in intron 13.

Epidemiologic data show considerable variation in the prevalence of primary lactase deficiency in different populations. In Northern European countries, where the prevalence of the -13910 T allele is high, lactase persistence is the norm and cases of lactose intolerance are relatively uncommon. In contrast, primary lactase deficiency is much more prevalent in Asian, African and South American populations where the -13910 C allele predominates.