Myocardial infarction (MI) is the leading cause of death in the developed world. Low-density lipoprotein cholesterol (LDL-C) is a causal risk factor for the disease. Despite aggressive use of LDL-C-lowering medications such as statins, many individuals do not achieve the LDL-C levels recommended by clinical guidelines. There remains a need for additional methods of reducing LDL-C and MI risk. In rare families, extremely low or high LDL-C segregates in a Mendelian fashion and the study of such families has transformed our understanding of LDL biology and has suggested new therapeutic targets. However, in many such families, sequencing of known causal genes has failed to identify mutations. Recently, there has emerged a powerful and efficient method to discover genes underlying rare Mendelian disorders, namely exome sequencing. Exome sequencing refers to the sequencing and analysis of all protein-coding regions in the human genome. We hypothesize that: (1) additional novel genes responsible for Mendelian forms of low or high LDL-C exist;(2) the causal gene and mutation(s) in each family may be discovered with exome analysis of just a few affected individuals in each pedigree;and (3) the newly discovered genes can be demonstrated to relate not only to LDL-C but also to MI risk in the population. To test these hypotheses, we propose the following Specific Aims: (1) To perform sequencing of the exome in 2-4 affected individuals from each of 11 families with familial hypobetalipoproteinemia (FHBL) and discover the causal gene and mutation specific to each family. FHBL is a disorder characterized by extremely low levels of plasma LDL-C. We will only study families where known causes of FHBL (e.g., APOB and PCSK9) have been ruled out;(2) To perform sequencing of the exome in 2-4 affected individuals from each of 10 families with severe hypercholesterolemia and discover the causal gene and mutation specific to each family. We will study families where known causes of hypercholesterolemia (e.g., APOB, PCSK9, and LDLR) have been ruled out;and (3) To perform targeted sequencing of novel genes mapped in Aims 1 and 2, discover intermediate frequency variants with large effect on LDL-C, and test these variants for association with MI risk in the population. Successful completion of this proposal should have three major impacts on biomedical research. First, we will discover a set of novel genes that when perturbed in humans lead to dramatically high or low LDL-C. Second, we will know which of these genes change not only plasma LDL-C but also MI risk. This information will allow for rational selection among potential molecular targets for those most likely to successfully produce effective and safe therapeutics. Finally, gene discovery should fuel additional mechanistic studies that can provide new insights into LDL-C metabolism and MI risk.

Public Health Relevance

Higher blood levels of low-density lipoprotein (LDL) cholesterol cause heart attack and new therapies are needed to lower blood LDL cholesterol. In some families, extremely high blood LDL cholesterol or extremely low blood LDL cholesterol tracks as if a single gene is defective. Here, we propose to identify the causal genes in such families by using a newly developed technique where all of the protein coding genes in the genome - the exome- can be sequenced in one experiment. After identifying the causal genes in families, we will test whether these genes influence risk for heart attack in the general population.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL107816-04
Application #
8644306
Study Section
Genetics of Health and Disease Study Section (GHD)
Program Officer
Hasan, Ahmed a K
Project Start
2011-05-16
Project End
2016-03-31
Budget Start
2014-04-01
Budget End
2015-03-31
Support Year
4
Fiscal Year
2014
Total Cost
$531,649
Indirect Cost
$85,000
Name
Massachusetts General Hospital
Department
Type
DUNS #
073130411
City
Boston
State
MA
Country
United States
Zip Code
02199
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Tada, Hayato; Won, Hong-Hee; Melander, Olle et al. (2014) Multiple associated variants increase the heritability explained for plasma lipids and coronary artery disease. Circ Cardiovasc Genet 7:583-7
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TG and HDL Working Group of the Exome Sequencing Project, National Heart, Lung, and Blood Institute; Crosby, Jacy; Peloso, Gina M et al. (2014) Loss-of-function mutations in APOC3, triglycerides, and coronary disease. N Engl J Med 371:22-31
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Peloso, Gina M; Auer, Paul L; Bis, Joshua C et al. (2014) Association of low-frequency and rare coding-sequence variants with blood lipids and coronary heart disease in 56,000 whites and blacks. Am J Hum Genet 94:223-32
Stitziel, Nathan O; Fouchier, Sigrid W; Sjouke, Barbara et al. (2013) Exome sequencing and directed clinical phenotyping diagnose cholesterol ester storage disease presenting as autosomal recessive hypercholesterolemia. Arterioscler Thromb Vasc Biol 33:2909-14
(2013) Common variants associated with plasma triglycerides and risk for coronary artery disease. Nat Genet 45:1345-52

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