Polymorphism of the 4-hydroxylation of debrisoquine in the San Bushmen of southern Africa.

1. The metabolic oxidation of debrisoquine has been studied in a group of 96 San Bushmen. 2. The amounts of debrisoquine and 4-hydroxy-debrisoquine excreted in 0-8 h urine were measured and the metabolic ratio (% dose as debrisoquine/% dose as 4-hydroxy-debrisoquine) calculated. 3. On the basis of Caucasian criteria, that metabolic ratios greater than 12.6 represent poor metabolizers, 19% of the Bushmen were poor metabolizers in contrast to the 8-10% found in Caucasian studies. 4. Probit plots showed four modes may be present in the data, which may represent at least three isozymes of the relevant enzyme which may also differ from the Caucasian isozymes.