Ethnicity, consanguinity, and genetic architecture of hypertrophic cardiomyopathy

AIMS

Hypertrophic cardiomyopathy (HCM) is characterized by phenotypic heterogeneity that is partly explained by the diversity of genetic variants contributing to disease. Accurate interpretation of these variants constitutes a major challenge for diagnosis and implementing precision medicine, especially in understudied populations. The aim is to define the genetic architecture of HCM in North African cohorts with high consanguinity using ancestry-matched cases and controls.

METHODS AND RESULTS

Prospective Egyptian patients (n = 514) and controls (n = 400) underwent clinical phenotyping and genetic testing. Rare variants in 13 validated HCM genes were classified according to standard clinical guidelines and compared with a prospective HCM cohort of majority European ancestry (n = 684). A higher prevalence of homozygous variants was observed in Egyptian patients (4.1% vs. 0.1%, P = 2 × 10-7), with variants in the minor HCM genes MYL2, MYL3, and CSRP3 more likely to present in homozygosity than the major genes, suggesting these variants are less penetrant in heterozygosity. Biallelic variants in the recessive HCM gene TRIM63 were detected in 2.1% of patients (five-fold greater than European patients), highlighting the importance of recessive inheritance in consanguineous populations. Finally, rare variants in Egyptian HCM patients were less likely to be classified as (likely) pathogenic compared with Europeans (40.8% vs. 61.6%, P = 1.6 × 10-5) due to the underrepresentation of Middle Eastern populations in current reference resources. This proportion increased to 53.3% after incorporating methods that leverage new ancestry-matched controls presented here.

CONCLUSION

Studying consanguineous populations reveals novel insights with relevance to genetic testing and our understanding of the genetic architecture of HCM.

Homozygosity predominantly affects hypertrophic cardiomyopathy minor genes in an Egyptian clinical cohort

Background

Consanguinity is prevalent in Egypt (35%) resulting in a high incidence of homozygosity. The influence of homozygosity on the genetics of Hypertrophic Cardiomyopathy (HCM) has not been adequately studied.

Purpose

The purpose of this study is to define the genetic architecture of HCM in Egypt using ethnically-matched case and control cohorts.

Methods

Prospective Egyptian patients (n=514) and controls (n=400) were recruited to Aswan Heart Centre for clinical phenotyping and genetic testing for 174 genes implicated in inherited cardiac conditions (Illumina). Rare variation (gnomAD filtering allele frequency ≤4x10–5) in 13 validated HCM genes were classified according to the American College of Medical Genetics (ACMG) guidelines and compared with a prospective HCM cohort of predominantly European ancestry (n=684).

Results

Significantly fewer rare variants detected in Egyptian patients could be classified as (likely) pathogenic compared to Europeans (40.8% vs. 61.6%, p-value=1.6x10–5). Incorporating analysis from these Egyptian case-control cohorts into the ACMG guidelines increased this yield to 53.8%. Homozygous variants were more frequently observed in Egyptian patients (4.1% vs 0.1%, p-value=2x10–7), with variants in the minor HCM genes MYL2, MYL3 and CSRP3 more likely to present in homozygosity than the major genes (MYH7, MYBPC3 and troponins), suggesting such variants are less penetrant in the heterozygous state.

Conclusions

The integration of Egyptian-specific genetic and phenotypic data significantly improves variant interpretation in HCM and consequently the precision of genetic testing. The observed prevalence of homozygosity and rare variation in minor HCM genes in Egyptian patients provides important insights into its disease-mechanisms and genetics.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Science and Technology Development FundAl Alfi Foundation

Profiling Genome-Wide DNA Methylation Patterns in Human Aortic and Mitral Valves

Cardiac valves exhibit highly complex structures and specialized functions that include dynamic interactions between cells, extracellular matrix (ECM) and their hemodynamic environment. Valvular gene expression is tightly regulated by a variety of mechanisms including epigenetic factors such as histone modifications, RNA-based mechanisms and DNA methylation. To date, methylation fingerprints of non-diseased human aortic and mitral valves have not been studied. In this work we analyzed the differential methylation profiles of 12 non-diseased aortic and mitral valve tissue samples (in matched pairs). Analysis of methylation data [reduced representation bisulfite sequencing (RRBS)] of 16,101 promoters genome-wide revealed 584 differentially methylated (DM) promoters, of which 13 were reported in endothelial mesenchymal trans-differentiation (EMT), 37 in aortic and mitral valve disease and 7 in ECM remodeling. Both functional classification as well as network analysis showed that the genes associated with the DM promoters were enriched for WNT-, Cadherin-, Endothelin-, PDGF-, HIF-1 and VEGF- signaling implicated in valvular physiology and pathophysiology. Additional enrichment was detected for TGFB-, NOTCH- and Integrin- signaling involved in EMT as well as ECM remodeling. This data provides the first insight into differential regulation of human aortic and mitral valve tissue and identifies candidate genes linked to DM promoters. Our work will improve the understanding of valve biology, valve tissue engineering approaches and contributes to the identification of relevant drug targets.

TORCH screening in pregnancy. Where are we now? An audit of use in a tertiary level centre

This audit was performed in the obstetrics and gynaecology department of a tertiary referral hospital, to investigate the use and results of TORCH screening. St Michael's Hospital delivers approximately 6,000 women from South Bristol a year and receives tertiary referrals from the South West of England and South Wales. It was found that 739 patients over a 6-year period from April 2006 to January 2012 underwent testing. The majority's indication (21%) was polyhydramnios. Three patients had evidence of primary CMV infection in pregnancy on serology, two for fetal indications (polyhydramnios and echogenic bowel) and one following a miscarriage. There were no confirmed cases of gestational toxoplasma or rubella. Routine testing for toxoplasma and rubella infection as part of the TORCH screening in cases of fetal or obstetric abnormality should thus be discontinued in our population.