PGxCheck...What is our DNA saying?




We need to consider how genetic information

can help us with respect to healthcare. We are able to perform genetic testing more readily,

but how are we using the results? Join in the discussion!


Personalized medicine and pharmacogenomics (the influence of genetics on drugs) is here. It is in its infancy and we all will watch it grow. From healthcare professionals to the general public, pharmacogenomics and the broader area of personalized medicine will present a learning curve.

This blog is made possible through an individual making their genetic information available. 

As we learn what this individual's genetics are telling us...and what it is not telling us, we will discuss it. I am sure there will be many questions. We will have individuals from pharmacy, genetics, ethics, law, and other disciplines adding their expertise and thoughts to the discussion. I sincerely hope you will contemplate the information, formulate your thoughts, and participate in the discussion!

A preliminary look at drug response: Caffeine

Here is my first entry related to drug response. I am starting off with a result that is supported only by one study...not the strongest of data, but interesting nonetheless. I know that some of the terminology can be difficult, so I "cleaned the background information up a bit! I added a few [bracketed] comments. Note, use an online medical dictionary to look up some of the terms you may not be familiar with.

Coffee, CYP1A2 [CYP = cytochrome P450, a metabolizing enzyme] genotype, and risk of myocardial infarction.


Department of Nutritional Sciences, University of Toronto, Toronto, Ontario, Canada.



The association between coffee intake and risk of myocardial infarction (MI) remains controversial. Coffee is a major source of caffeine, which is metabolized by the polymorphic cytochrome P450 1A2 (CYP1A2) enzyme. Individuals who are homozygous for the CYP1A2*1A allele are "rapid" caffeine metabolizers, whereas carriers of the variant CYP1A2*1F are "slow" caffeine metabolizers.


To determine whether CYP1A2 genotype modifies the association between coffee consumption and risk of acute nonfatal MI.


Cases (n = 2014) with a first acute nonfatal MI and population-based controls (n = 2014) living in Costa Rica between 1994 and 2004, matched for age, sex, and area of residence, were genotyped by restriction fragment-length polymorphism polymerase chain reaction. A food frequency questionnaire was used to assess the intake of caffeinated coffee.


Relative risk of nonfatal MI associated with coffee intake, calculated using unconditional logistic regression.


Intake of coffee was associated with an increased risk of nonfatal MI only among individuals with slow caffeine metabolism, suggesting that caffeine plays a role in this association.

Here is what 23andMe posted in  my results:

Caffeine Metabolism

Some people get jumpy after drinking a single cup of coffee, while others can gulp down a Venti Americano [what is this?] without feeling a thing. Part of that variability is due to the development of tolerance by regular coffee drinkers; but there are genetic differences in how people metabolize caffeine as well.

The following results are based on  Preliminary Research for 1 reported marker.

Caffeine and MI risk

Caffeine MI_2

I find this interesting, because if I drink a cup of coffee, which I don't regularly at all, let alone a Venti Americano, I get so 'jittery' I can't stand it. Also, I once took a dose of a drug called theophylline for a study and I could not come close to sleeping! See if you can find out how theophylline is related to caffeine!

At any rate, my genetics say I am a 'fast caffeine metabolizer'. Thank goodness!

6 comments | Add a New Comment
1. Hayley Sayre | October 06, 2013 at 01:19 AM EDT

Theophylline is a member of the xanthine family, which shows that it is structural and pharmacological similar to caffeine. Theophylline is naturally found in cocoa beans, which are an ingredient in coffee. This shows that the reason you could not sleep is because this substances resembles caffeine, so if you get really jittery by drinking coffee, when you took this drug is had a very similar effect on you.

2. Katlyn Brown | October 06, 2013 at 11:02 AM EDT

Theophylline bears structural and pharmacological similarity to caffeine. By increasing heart rate and blood prressure it acts similar to how caffeine does in your body making you jittery and unable to sleep.

3. Kara Horvath | October 06, 2013 at 04:10 PM EDT

I understand that caffeine can be metabolized quickly or slowly and makes some people \jittery\. But, some people say that coffee/caffeine ONLY makes them tired, which is the opposite effect of typical caffeine. What factors cause this on the cellular level?

4. DFK | October 07, 2013 at 09:58 AM EDT

While not an expert here, I have this minimal understanding. There may be a 'energy deficit' or 'energy crash' after caffeine. This may be due to caffeine's (and theophylline's) effect of blocking adenosine. The body 'corrects' this and produces more adenosine. Adenosine receptors in the brain have altered effects in different parts of the brain. Early stimulation is followed by a 'wear-off'. Some people do not 'recognize the stimulation or it is not pronounced, but do recognize the post caffeine 'crash'.This is only part of a much larger biochemical story.

Caffeine and theophylline alter blood flow and perfusion to the different organs (e.g., the liver and brain;; and other organs and can alter cerebral blood flow by blocking adenosine, resulting in constriction of blood vessels (

Finally, caffeine acts as a diuretic and can cause people to lose sleep to go to the bathroom. This can make then tired in the morning.

5. Joshua Macks | October 17, 2013 at 07:03 PM EDT

I understand that caffeine has different effects on different people, and I am sure that this is due to differences in a gene. My question is, has the gene that causes different reactions to caffeine been identified? If so, which gene is it?

6. Kole Wallace | March 15, 2014 at 04:46 PM EDT

I think this explains my high tolerance for caffeine. Whenever I drink an energy drink it never seems to effect me, but I've seen some of my friends bounce off of the walls after a Red Bull. I must have a high caffeine metabolism.

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