GENETIC RISK MARKERS
Genetic Medicine is a rapidly evolving field which allows us to identify personalized features that exist amongst each of us which make us unique. It helps to answer the sort of questions "why is it that two people can both live an equally unhealthy lifestyle, but, only one will develop the disease?", or "why don't all people respond the same way to a given medication even though they are making the same positive lifestyle changes and taking the same treatment drug and dosage?".
We are now identifying ways to identify high risk heart patients before they present with significant heart disease. That is important because approximately, 40-50% of people with coronary disease present for the first time with sudden death without ever having known that they had any sort of problem.
Until now, there have been limitations in the primary tools which we have been utilizing to assess our patients. Many patients with normal LDL cholesterol can still have heart attacks.
The Framingham risk score is a useful tool for identifying patients at risk. Unfortunately, it reflects the “average person” and is imperfect at identifying the “individual patient” who may have unique features that place him at high risk.
Consequently, the American Heart Association and the Canadian Cardiovascular Society have begun to advocate the use of some novel modalities that may be reserved for refining risk estimates in our patients who are at intermediate risk of vascular events. Some of these modalities are biochemical lab tests (see section on Inflammatory Markers of heart disease), while others are genetic markers some of which are discussed below.
The application of genetic screening may help us to identify those patients who may be genetically predisposed to certain cardiovascular conditions later in life and to help in identifying patients who may respond better to one medication rather than to another. Some of these tests are currently available in Canada.
It is important to remember that having a "bad gene" is not necessarily a "done deal". It simply means that you are at risk for a future problem. The current thinking of genetic specialists is that we can modify these predetermined risks by changing our environmental exposures to things like proper sleep, exercise, diet, and stress, etc. So, genetic testing is not necessarily something to be feared, but, rather embraced for those of us who are prepared to use the information in a positive way.
This gene codes for the production of a type of lipoprotein (apoE) that is associated with high cholesterol levels and increased cardiovascular disease. Depending on the type of ApoE, the response to cholesterol lowering strategies may vary.
LpA Intron25 gene
This variant is associated with coronary disease and determines Lp(a) blood levels. It is associated with increased cardiovascular risk (1.5x)
This gene is associated with an increased risk of premature coronary disease, and abdomial aortic aneurysm. (the risk is 1.5x if 1 allele, 2x if 2 alleles).
This gene when present may be associated with an increased risk of cardiovascular event. But, it is also associated with a good response to treatment with either lipitor or pravachol
Patients with this genotype have a higher risk of cardiovascular events and respond well to aspirin therapy
This is referred to as the “statin tolerance gene” and individuals with this genotype may be at increased risk of adverse effects from statins (cramps/cpk elevation) on muscles.
In 2013, evidence was published illustrating that carriers of this genotype had a 4x risk of complications when taking 80mg/day of zocor, or 2x risk of complications on 40mg/day of zocor.
There are two SNPs that are associated with increased risk of Atrial fibrillation and are more common than we might have expected (ie. 20-30% of the population depending on ethnicity). One SNP (rs2200733) is associated with a 1.7x chance of atrial fibrillation. Perhaps looking for these SNPs maybe useful in a patient with an unexplained stroke where you suspect but havent proven the presence of atrial fibrillation.
This is a gene that codes for a type of enzyme (cytochrome P450) which is involved in metaboliizing certain medications like plavix into its activated form.
Individuals with either 1 or 2 of one of these genetic variants appear to respond poorly to plavix and have an increased risk of cardiovascular events and/or stent thrombosis while taking plavix
IndIviduals with either 1or 2 of the other genetic variant appear to respond too well to plavix and are more prone to bleeding on it.