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.
Hussein et al. (1982) studied lactose absorption in 570 health adolescent and adult males in Egypt. Employing a field version of the noninvasive hydrogen breath test, 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 regional distribution showed significant differences between the Nile Delta and the northern and southern part of Upper Egypt. Hussein et al. (1982) also 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) conducted lactose tolerance tests with breath hydrogen determination and 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 Kuwaiti and Asian adults. A total of 70 Kuwaiti and 70 matched Asian volunteers were administered to the Breath Hydrogen Test (BHT) after a lactose challenge following an overnight fast. 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.
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 with multiple breath collection and gas chromatographic hydrogen determination. The subjects were divided according to the geographic areas and to the tribes into North Nile (Nubians, Dongolawi, Shaygi), central Sudan (Jaali), Northern Nomads (Gomoeia, Kahli, Bedja), Baggara (Misseri, Habbani), Aboriginal Negroid (Nuba), and Southern Sudan (Nilotics). Lactose malabsorbers (LM) were accounts for 55.1% of the total subjects with a change of H2 concentration over 16 vpm. 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.