Decreased levels of BAG3 in a family with a rare variant and in idiopathic dilated cardiomyopathy

Abstract

The most common cause of dilated cardiomyopathy and heart failure (HF) is ischemic heart disease; however, in a third of all patients the cause remains undefined and patients are diagnosed as having idiopathic dilated cardiomyopathy (IDC). Recent studies suggest that many patients with IDC have a family history of HF and rare genetic variants in over 35 genes have been shown to be causative of disease. We employed whole-exome sequencing to identify the causative variant in a large family with autosomal dominant transmission of dilated cardiomyopathy. Sequencing and subsequent informatics revealed a novel 10-nucleotide deletion in the BCL2-associated athanogene 3 (BAG3) gene (Ch10:del 121436332_12143641: del. 1266_1275 [NM 004281]) that segregated with all affected individuals. The deletion predicted a shift in the reading frame with the resultant deletion of 135 amino acids from the C-terminal end of the protein. Consistent with genetic variants in genes encoding other sarcomeric proteins there was a considerable amount of genetic heterogeneity in the affected family members. Interestingly, we also found that the levels of BAG3 protein were significantly reduced in the hearts from unrelated patients with end-stage HF undergoing cardiac transplantation when compared with non-failing controls. Diminished levels of BAG3 protein may be associated with both familial and non-familial forms of dilated cardiomyopathy.

Figure 1

BAG3-Associated Dilated Cardiomyopathy Pedigree. Males are represented by squares. Circles indicate females. Open symbols represent unaffected individuals and black symbols represent affected individuals. The presence or absence of the 10-nucleotide deletion in BAG3 is indicated by either a (+) or a (−) respectively. An arrow denotes the proband. An asterisk is used to denote individuals whose DNA was used for whole exome sequencing. A diagonal line is used to denote individuals who are deceased.

Figure 2

A: Sequencing alignment for BAG3 10-nucleotide deletion. B: Representative Sanger sequencing shows the deletion in the BAG3 gene in an affected individual.

Figure 3

Representative Western blot of BAG3 and GAPDH levels in non-failing (NF) and failing (F) human heart. C. Quantification of BAG3 protein levels in non-failing and failing human heart. Values are normalized to the level of GAPDH in order to account for variations in protein loading. Horizontal lines represent mean and standard error of the mean. Statistical analysis was performed using unpaired t-test with Welch’s correction for unequal variance,