Genetic hypolactasia (primary lactose intolerance) is a genetic disorder that is characterized by the inability of lactase in the mucous membrane of the small intestine to digest lactose into glucose and galactose. The disaccharide lactose is found in milk and processed foods. Therefore, patients with this condition must avoid consumption of these types of food. The disease usually appears at 20-40 years of age because the enzyme activity declines with aging. Patients with primary lactose intolerance have loose stools, abdominal bloating and pain, flatulence, nausea, and borborygmi. Lactose intolerance is the most common enzyme deficiency worldwide with the highest prevalence rates among individuals of African origin. Males and females are equally affected.
Genetic hypolactasia is inherited as an autosomal recessive disorder. A non-coding mutation in the minichromosome maintenance (MCM6) gene affects the transcription of the lactase (LCT) gene. This results in down-regulation of lactase activity and the symptoms of hypolactasia.