Polymorphic acetylation of sulphamethazine in rural bedouin and urban-dwellers in Saudi Arabia.

1. The polymorphic acetylation of sulphamethazine (sulphadimidine, sulphamezathine) has been investigated in a population of 109 Saudi male arabs of rural bedouin origin and in 126 Saudi female arabs from urban cosmopolitan areas of Jeddah. 2. Rural males excreted 5-79% of the administered dose (1 X 5 g/m2 body surface area) in the 0-12 h urine and the urban females excreted 5-97%. 3. The frequency distribution of the ratio acetyl sulphamethazine/sulphamethazine was bimodal in rural, urban and the combined populations with a clear antimode at 70% acetylation of the recovered dose. 4. The incidence of slow acetylators was 67 X 9, 59 X 5 and 63 X 4% in the rural, urban and combined populations. The incidence of the As allele in Saudi arabs was thus 0 X 80+/-0 X 03 S.E.M., which is similar to that found in the neighbouring countries, of Egypt and Sudan. Since no significant difference in As frequency was apparent between the rural (pure) and urban (cosmopolitan) arabs, it is concluded that immigrants to Saudi Arabia from other muslim countries have not affected the gene frequencies with respect to acetylation. 5. Methodology of assessing acetylation phenotype is discussed. It would appear that urine analysis alone gives satisfactory discrimination between phenotypes.