A study found that attention-related responses to d-amphetamine differed across COMT genotype groups. The association is evidence about variability in a research sample, not a validated genetic test for predicting an individual’s cognitive response.
Hamidovic and colleagues studied 161 healthy young adults of European ancestry. Participants received placebo and 10- and 20-mg d-amphetamine doses in a counterbalanced, double-blind design. The study examined Digit-Symbol Substitution Test performance and, in a smaller subset, deviations from the typical reaction time as an attention-lapse measure.
A blood sample was collected for genotyping. That specimen identified inherited variation; it was not a measured amphetamine concentration serving as an impairment threshold.
Genotype groups did not differ significantly on the digit-symbol task under placebo. They did differ on the attention-lapse measure, with met/met participants showing fewer lapses than participants carrying a val allele.
D-Amphetamine improved the reported task measures in val/val and val/met groups, while corresponding benefits were not demonstrated in the met/met group. Mood responses did not show the same genotype-related differences.
The absence of a baseline digit-symbol difference shows that a genotype association can depend on the endpoint. A smaller response to a drug also does not necessarily imply poorer function, particularly when baseline performance differs.
The attention-lapse analysis involved only a subset of the original sample. Age and caffeine-related factors required consideration, and the restricted ancestry and healthy-volunteer selection limit generalization.
The paper does not establish diagnostic accuracy for predicting benefit, impairment or medication requirements in a new person. It does not justify substituting a genotype for observed functioning or an exposure history.
Its contribution is to show that stimulant effects can vary with participant characteristics and task demands. Clinical and forensic conclusions still require evidence specific to the person, the function and the circumstances.
Related reading: Selected performance improvements in human methamphetamine experiments.