Distribution of human adult lactose phenotypes in Egypt.

Lactose absorption was studied 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. The existence of a north-south gradient of decreasing frequencies of the hypolactasia gene from the Nile Delta to the Sudan is suggested.