Formin homology 2 domain containing 3 variants associated with hypertrophic cardiomyopathy

Abstract

Background: Incomplete penetrance and variable expression of hypertrophic cardiomyopathy (HCM) is well appreciated. Common genetic polymorphisms variants that may affect HCM penetrance and expression have been predicted but are not well established.

Methods and results: We performed a case-control genomewide association study to identify common HCM-associated genetic polymorphisms and then asked whether such common variants were more represented in HCM or could explain the heterogeneity of HCM phenotypes. We identified an intronic FHOD3 variant (rs516514) associated with HCM (odds ratio, 2.45; 95% confidence interval, 1.76-3.41; P=1.25×10(-7)) and validated this finding in an independent cohort. Next, we tested FHOD3-V1151I (rs2303510), a nonsynonymous variant in partial linkage disequilibrium with rs516514, and we detected an even stronger association with HCM (P=1.76×10(-9)). Although HCM patients were more likely to carry these, FHOD3 allele subjects homozygous for FHOD3-1151I had similar HCM phenotypes as carriers of the V1151 allele. FHOD3 expression is increased in the setting of HCM, and both alleles of FHOD3-V1151I were detected in HCM myectomy tissue. Previously, FHOD3 was found to be required for formation of the sarcomere, and here we demonstrate that its fly homolog fhos is required for normal adult heart systolic contraction.

Conclusions: Here we demonstrate the association of a common nonsynonymous FHOD3 genetic variant with HCM. This discovery further strengthens the potential role of gene mutations and polymorphisms that alter the amino acid sequence of sarcomere proteins and HCM.

Figure 1

Chromosome 18 locus that includes FHOD3 is associated with HCM. A. Graph shows the − log(p-value) and the location of each SNP contained on the 370CNV array that is within the chromosome 18 locus identified by the HCM GWA study. The SNP with the strongest association with HCM is shown in blue. SNPs in LD with rs516514 are shown from red (strong LD) to yellow (weak LD). Relative sites of recombination are shown in blue lines. B. Quantitative real time PCR demonstrating expression of FHOD3 RNA in mouse tissues. The strongest expression was found in the heart. C. Alignment of FHOD3 peptide showing conservation of FHOD3-V1151 (red box) in mammals. Amino acids conserved across all species shown are marked by asterisk.

Figure 2

FHOD3 expression in heart and HCM tissue. A. Quantitative PCR analysis demonstrates significantly increased expression of FHOD3 transcript in heart tissue from 19 HCM case hearts and 17 controls. B. Quantitative Western blot analysis demonstrates significantly increased expression of FHOD3 protein in heart tissue from six HCM cases compared with six controls. C. Sequence analysis of the FHOD3 transcript in human myectomy samples demonstrates the presence of both nucleotide alleles of rs2303510 (green and black peaks at the position marked by arrow) indicating that both peptide forms of FHOD3-V1151I may be expressed. Asterisk, p<0.05.

Figure 3

Decrease in fhos expression produces reduced fly heart contraction. Fly heart contractile function in flies expressing the fhos RNAi in the heart was examined by optical coherence tomography (OCT). Compared with control hearts (n=21) flies expressing the fhos RNAi in the heart (n=21) showed increased A. end-diastolic dimension, B. end-systolic dimension and C. reduced fractional shortening. D. representative OCT images from control and fhos RNAi flies. Asterisk, p<0.05.