Page "Pharmacogenetics" Paragraph 17

Around 10 % of people are heterozygous-they carry one variant allele-and produce a reduced quantity of functional enzyme.

Overall, they are at greater risk of adverse effects, although as individuals their genotype is not necessarily predictive of their clinical outcome, which makes the interpretation of a clinical test difficult.

Recent research suggests that patients who are heterozygous may have a better response to treatment, which raises whether people who have two wild-type alleles could tolerate a higher therapeutic dose.