Previous human genetic studies have identified the etiology of many heritable cardiovascular disorders. Hypertrophic cardiomyopathy (HCM), the most common heritable cardiovascular disorder (prevalence 1:500), has been associated with mutations in at least 19 genes, most of which encode sarcomere proteins, along with a few encoding Z-disc and calcium handling proteins. However, mutations are detected in previously identified genes in only ~50% of patients. Therefore, we hypothesize that variants in other heretofore undiscovered genes that regulate the sarcomere, the Z-disc, or cellular calcium homeostasis, including metabolic genes, can directly cause disease. Large scale forward genetics in mice is a novel approach to identifying these undiscovered genes. The NHLBI has funded a mouse ethylnitrosourea (ENU) mutagenesis program that is identifying genetic pathways contributing to congenital heart disease. Preliminary studies show that 6% of fetuses homozygous for a given mutation have isolated cardiac hypertrophy. Therefore, our overall objective is to leverage the unique resource available to us through this ENU mutagenesis program to recover novel genes associated with HCM.
Our specific aims are: 1. To recover ENU mutagenized mouse pedigrees with HCM. Pedigrees exhibiting HCM in the homozygous state in fetuses will be interrogated for the presence of the disease phenotype in the heterozygous state in adults, specifically, abnormalities on echocardiograms and histopathology characteristic of HCM. Phenotypes evident in the heterozygous state are more likely to be clinically relevant. 2. To identify novel genes with mutations leading to HCM. Abnormal heterozygous adults will be genotyped to exclude mutations in genes previously associated with HCM and functionally related genes, using sequence capture arrays. We will select ~6 pedigrees with potentially novel genetic mutations (including an HCM pedigree that we have already identified). From 2 of these pedigrees, we will identify mutations in novel genes using massively parallel whole genome sequencing. This exploratory proposal is meant to establish a foundation for multiple future studies: banking of pedigrees of interest for further analysis by the wider scientific community;expansion of this strategy, once proven, to larger cohorts of mice;further mechanistic studies of novel mutations in mice and other model systems;determination of the role of novel genetic variants in our large pre-existing cohorts of human subjects with HCM. We feel that it is imperative for us to pursue the proposed project, so that the opportunity for both us and other investigators to study mouse pedigrees with HCM that are generated by this ENU mutagenesis program is not wasted.
Inherited genetic mutations leading to abnormal thickening of the muscle of the heart are among the most common causes of sudden death, particularly in the young. Although enormous progress has been made in the past 20 years to identify the genetic causes of this disorder, approximately half of all patients do not have an identified cause. Studying mice, this project will identify some of these unknown causes of inherited heart disease. These findings will allow physicians to determine who is at high risk of sudden death and to intervene early to prevent death. In the long term, these findings will lead to the development of improved treatments.
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