Lactase Intolerance, Adult Type

Alternative Names

  • Disaccharide Intolerance III
  • Adult Lactase Deficiency
  • Lactose Intolerance
  • Hereditary Persistence of Intestinal Lactase
  • Hypolactasia, Adult Type

Associated Genes

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WHO-ICD-10 version:2010

Endocrine, nutritional and metabolic diseases

Metabolic disorders

OMIM Number


Mode of Inheritance

Autosomal recessive

Gene Map Locus



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.

Epidemiology in the Arab World

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Other Reports


Hussein et al. (1982) studied lactose absorption in 570 health adolescent and adult males in Egypt.A total of 156 (27.4%) lactose absorbers and 414 (72.6%) lactose malabsorbers were identified. The age-specific prevalence of the lactose phenotypes indicated that lactase repression is complete at the age of 14 years in Egyptians. The authors suggested the existence of a north-south gradient of decreasing frequencies of the hypolactasia gene from the Nile Delta to the Sudan.


Hijazi et al. (1983) identified 39 lactose malabsorbers among 162 Jordanian Bedouins (24%), and 111 lactose malabsorbers among 148 subjects from the urban/agricultural zone of western Jordan and Palestine (75%). This highly significant difference supports the hypothesis that milk dependence in nomadic desert populations resulted in selective pressures in favor of the lactase persistence gene. Within the urban/agricultural zone which extends from the desert border in Jordan to the Mediterranean shore, a significant increase in the frequency of lactose malabsorbers (and hypolactasia gene frequencies) from east to west was observed. The suggested genetic cline is problably due to migration from the desert populations to the agricultural zone.


Al Sanae et al. (2003) compared the incidence of lactose intolerance between 70 Kuwaiti and 70 matched Asian adult volunteers.  The results showed a comparatively higher basal BHT level among the Kuwaiti subjects, although the Asians had a slightly higher positive result (58% compared to 47% among the Kuwaitis). Overall, positive BHT was found to be a good indicator of clinical symptoms. Flatulence, abdominal pain, and diarrhea seemed to have a stronger association with a positive BHT.


Nasrallah (1979) performed lactose tolerance tests on 74 healthy Lebanese volunteers and 12 patients with mediterranean lymphoma. Of the healthy subjects, 78% were found to have lactose malabsorption, whereas all the lymhoma patients were lactose intolerant. 


See: Jordan > Hijazi et al., 1983.


Bayoumi et al. (1981) studied the distribution of lactase phenotypes in the population of Sudan. The study included 549 males and 14 females who were subjected to lactose tolerance test. Lactose malabsorbers (LM) accounted for 55.1% of the total subjects. Accordingly, the frequency of the hypolactasia gene was 0.742. Nomadic pastoralists had the lowest prevalence rate of LM (38.1%), whereas the highest rates were among the residential agriculturalists of aboriginal Negroid (76.2%) and the North Nile (64.1%). In central Sudan, the relatively low prevalence of LM (47.9%) might be attributed to the migration from nomadic populations to the central Sudan. All groups showed frequencies of the hypolactasia gene greater than 0.5. In all subgroups, with the possible exception of Bedja, the hypolactasia gene was more frequent than the lactase persistence gene. A considerable "dilution" of the frequency of hypolactasia gene in the Nile valley population was expected due to increased migrations of Bedja tribe population to the Nile valley. These findings supported the claim that in the Old World, only few populations outside the central and Northern Europe have lactase persistence gene frequencies greater than 0.5.

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