A common MYBPC3 (cardiac myosin binding protein C) variant associated with cardiomyopathies in South Asia

Abstract

Heart failure is a leading cause of mortality in South Asians. However, its genetic etiology remains largely unknown. Cardiomyopathies due to sarcomeric mutations are a major monogenic cause for heart failure (MIM600958). Here, we describe a deletion of 25 bp in the gene encoding cardiac myosin binding protein C (MYBPC3) that is associated with heritable cardiomyopathies and an increased risk of heart failure in Indian populations (initial study OR = 5.3 (95% CI = 2.3-13), P = 2 x 10(-6); replication study OR = 8.59 (3.19-25.05), P = 3 x 10(-8); combined OR = 6.99 (3.68-13.57), P = 4 x 10(-11)) and that disrupts cardiomyocyte structure in vitro. Its prevalence was found to be high (approximately 4%) in populations of Indian subcontinental ancestry. The finding of a common risk factor implicated in South Asian subjects with cardiomyopathy will help in identifying and counseling individuals predisposed to cardiac diseases in this region.

Figure 1

Morphology and histopathology of heart, and cardiac transcript analysis of individuals with the 25-bp deletion. (a) Morphology of the heart of a subject with DCM. The subject was a child homozygous for the deletion. Note the marked dilation of the left and right ventricles. (b) Histopathological section of the same subject showing hypertrophied myofibers separated from each other by increased connective tissue (hematoxylin and eosin, × 400). (c) Transverse section through both ventricles of a 40-y-old man homozygous for the deletion showing marked asymmetric hypertrophy involving septum (IVS). (d) Histopathological section of the septal myocardium of the same individual showing ‘swirling’ of hypertrophied myofibers amid connective tissue disarray (hematoxylin and eosin, × 400). (e) Characterization of cardiac transcripts. The mRNA from the endomyocardial biopsies of an affected subject heterozygous for the 25-bp deletion was reverse transcribed, amplified, subcloned and sequenced. The sequence shows a normal transcript and a mutant transcript with absence of exon 33. AO, aorta; RA, right atrium; PA, pulmonary artery; RV, right ventricle; LV, left ventricle; TV, tricuspid valve; IVS, intraventricular septum; MV, mitral valve; AV, aortic valve.

Figure 2

Expression and localization of cMyBP-C^WT and cMyBP-C^ΔEx33 proteins in neonatal rat cardiomyocytes. Recombinant adenoviruses that expressed mouse cMyBP-C^WT (WT) or cMyBP-C^ΔEx33 (mutant) were introduced into rat neonatal cardiomyocytes. Noninfected cardiomyocytes were used as control. (a,b) Three days after infection, cardiomyocytes were fixed and immunostained with either cMyBP-C antibodies (green) (a) raised against the C0-C1 domain carried by native, WT and mutant proteins or myc-tag antibodies carried only by the WT and mutant proteins (green) (Roche) (b) and costained with α-tropomyosin (red) (Sigma). (c,d) Representative protein blots obtained by using cMyBP-C (c) and Myc (d) antibodies in control and WT- and mutant-infected neonatal rat cardiomyocytes. Twenty μg of total cardiomyocytes lysates was separated on a 4–15% linear gradient SDS-PAGE, transferred to nitrocellulose membrane, and immunoblotted as described in Supplementary Methods. In lysates from noninfected neonatal cardiomyocytes and WT-infected cells, the cMyBP-C antibody detected a major band of the expected molecular weight of 144 kDa and overexpression of mutant cMyBP-C showed the predicated truncated protein of approximately 140 kDa. α-TM was used as a load control.

Figure 3

Global distribution of MYBPC3 deletion in indigenous populations. For populations with the MYBPC3 deletion, the frequency of the deletion-containing allele is shown. See Supplementary Table 5 for details of the populations studied.