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Boston Heart conducts genotyping for the following: SLCO1B1 (statin induced myopathy), apoE, clopidogrel response (CYP2C19), prothrombin (factor II) G20210A, factor V Leiden, and MTHFR. These tests aid in the selection of appropriate treatment options for individuals.
The SLCO1B1 gene is critical to the body’s uptake and metabolism of statins, drugs prescribed to reduce LDL-C levels for the prevention of heart attacks or strokes. Statin Associated Muscle Symptoms (SAMS) are the number one adverse side effect of statins. 60% of patients who are prescribed statins stop taking the drug within one year. Studies estimate the risk of SAMS in clinical practice is about 7-29%, which causes a significant amount of non-compliance. About 25% of people carry either one or two copies of the SLCO1B1 variant which makes them four-to seventeen-times more likely to suffer statin induced myopathy (muscle pain, tenderness and weakness with elevated creatine kinase (CK) levels) as a side effect of statin therapy. Statin induced myopathy occurs in about 1% of patients on statins.
Apolipoprotein E (apoE) is a protein constituent of triglyceride-rich lipoprotein and HDL, and is important for the absorption of cholesterol, as well as the uptake of triglyceride-rich lipoproteins by the liver.
About 65% of the population has the normal form of apoE, apoE3/3. About 20% of the population has the abnormal form of apoE known as apoE4, while another 15% carry the abnormal form known as apoE2. Boston Heart’s apoE genotype test measures the genetic variants of apoE.
- ApoE4 is associated with increased cholesterol absorption in the intestine, increased uptake of intestinally derived and liver derived remnants of triglyceride-rich particle metabolism, and increased LDL-C. People with this form of apoE are more responsive to LDL-C lowering diets that are low in animal fat and cholesterol and to the cholesterol absorption inhibitor ezetimibe, and they are less responsive to statins for LDL-C lowering.
- ApoE2 is associated with decreased uptake of intestinally-derived and liver-derived remnants of triglyceride-rich lipoprotein metabolism, and lower LDL-C. People with this form of apoE are responsive to statins to lower LDL-C levels.
- Subjects with the uncommon apoE2/2 genotype, if they are in families also affected with familial combined hyperlipidemia, are at increased risk of developing marked elevations in blood cholesterol and triglyceride levels. This is due to increases in intestinally- and liver-derived remnants of triglyceride-rich lipoprotein metabolism. Such patients respond extremely well to statins, niacin, and fibrate therapy aimed at lipid lowering.
Clopidogrel is indicated in acute coronary syndrome, myocardial infarction, or those undergoing angioplasty with stent placement to prevent clot formation or closure of stents. There are certain genetic variants in the cytochrome P450 enzyme 2C19 necessary for converting clopidogrel to its active form in the bloodstream. Boston Hearts’ Clopidogrel Response 2C19 Genotyping test identifies those variants.
- About 40% of the population have the *1/*1 genotype, which is classified as normal. These subjects have a normal ability to metabolize clopidogrel. The standard dose of clopidogrel is recommended.
- About 30% of the population have the *1/*17 and *17/*17 genotypes and are classified as increased clopidogrel metabolizers and markedly increased clopidogrel metabolizers respectively. These subjects have increased metabolism of clopidogrel to its active form. Only normal doses of clopidogrel, if indicated, are recommended for individuals with the *1/*17 genotype, and only normal doses or lower than normal doses are recommended, if indicated, for individuals with the *17/*17 genotype.
- About 20% of the population have the *1/*2 and *1/*3 genotypes, and are classified as decreased clopidogrel metabolizers. These subjects have a decreased ability to metabolize clopidrogrel to its active form. The clopidogrel dose, if indicated, may need to be increased.
- About 2-3% of the population (higher in Asians) have the *2/*2, *2/*3, and *3/*3 genotypes, and are classified as markedly decreased clopidogrel metabolizers. These subjects have insufficient ability to metabolize clopidrogrel to its active form. Another agent such as ticagrelor or prasugrel, if indicated, is recommended.
- About 7% of the population have the *2/*17 and *3/*17 genotypes. Clopidogrel metabolism by people in this genotype is not known but is assumed to fall in the normal category. Normal doses of clopidogrel can be used.
Factor V Leiden and Prothrombin are clotting factors. Boston Heart Diagnostics provides tests for the Factor V Leiden genotype (about 5% of the population) and the prothrombin G20210A variant (about 3% of the population).
- People who inherit either of these variants have an increased risk of venous thromboembolism. This is especially true for those who inherit both genetic variants and are on oral estrogen therapy.
- Individuals affected with these variants may benefit from aspirin therapy.
MTHFR (methylenetetrahydrofolate reductase) is the enzyme responsible for metabolizing folate which, in turn, is essential for converting homocysteine to methionine. Homocysteine is an amino acid that plays an important role in metabolism, but high levels are related to a higher risk of coronary heart disease, stroke and peripheral vascular disease. The intended use of MTHFR genetic testing is, along with assessing homocysteine levels, to assess a patient’s risk for cardiovascular disease (CVD) and potentially minimize this risk through nutritional therapy and possibly clot prevention with low dose aspirin.