N-acetyltransferase 2 (NAT2) is the main enzyme metabolizing isoniazid and genotype-based treatment has been
studied for years without becoming common practice. To investigate whether genotype-based isoniazid treatment
is feasible in Greenland, we sequenced the coding sequence of NAT2 and determined the NAT2 enzyme-activity
by caffeine test.
No additional genetic variants were identified in the coding sequence of NAT2, so that genotype status in 260 study
participants could be assessed by a well-established 7-SNP panel. Studying the enzyme activity by the ratio of the
two caffeine metabolites AFMU and 1X in 260 participants showed a high rate of slow phenotypes with intermediate
or rapid genotype. These misclassifications were mainly observed in urine samples with pH<3, a deviation
from the standard protocol due to the field work character of the study, where immediate pH adjustment to pH=3.5
was not possible. We excluded these samples. For the remaining 143 individuals with pH>3, we observed a moderate
level of discrepancies (19 of the 116 individuals with intermediate or rapid genotype status having a slow
phenotype). Further investigation showed that drinking coffee and not tea or cola was the most important factor
for high levels of both metabolites.
The concordance between phenotype and genotype status with regard to slow metabolism supported the recommendation
of lower isoniazid doses in individuals with slow genotype status in order to avoid liver injury, a frequent
side effect. The phenotypical variation observed for individuals with intermediate or rapid genotype status
warrants further research before increased dosing of isoniazid can be recommended
