Question

Caffeine use has been linked to many physiological changes, including changes in heart rate. The following show the heart rate (beats per minute, bpm) results for 3 students at rest, and taken again at 30 minute intervals following ingestion of a standard dose (200mg) of caffeine.

STUDENT	Initial (bpm)	30 min post ingestion	60 minute post ingestion
Student 1	79	77	78
Student 2	81	88	95
Student 3	88	95	94

Choose the correct genotype/s for the CYP1A2 locus of each student, based on the test results.

The genotype choices are AA or AC, CC, AC or CC, AA or CC, AC, AA.

Answer 1

Caffeine is metabolized by the enzyme cytochrome P450 1A2 (CYP1A2). This enzyme has 2 allelic variants namely CYP1A2*1A and 1F. The CYP1A2*1A metabolizes caffeine faster than the second allele.

The persons who are homozygous for the allele CYP1A2*1F are slow metabolizers of caffeine.
The persons who are heterozygous for CYP1A2*1F/CYP1A2*1A are slow metabolizers of caffeine.
The persons who are homozygous for the allele CYP1A2*1A are fast metabolizers of caffeine.

The genotype choices are AA or AC, CC, AC or CC, AA or CC, AC, AA

Student 1 looks like slow metabolizer of caffeine, the genotype would be CC
Student 2 looks like medium metabolizer of caffeine, the genotype would be AC
Student 3 looks like fast metabolizer of caffeine, the genotype would be AA