The genetic component of bicuspid aortic valve and aortic dilation. An exome-wide association study.

BACKGROUND: Bicuspid aortic valve is the most common cardiovascular congenital malformation affecting 2% of the general population. The incidence of life-threatening complications, the high heritability, and familial clustering rates support the interest in identifying risk or protective genetic factors. The main objective of the present study was to identify population-based genetic variation associated with bicuspid aortic valve and concomitant ascending aortic dilation. MATERIALS AND METHODS: A cross-sectional exome-wide association study was conducted in 565 Spanish cases and 484 controls. Single-marker and gene-based association analyses enriched for low frequency and rare genetic variants were performed on this discovery stage cohort and for the subsets of cases with and without ascending aortic dilation. Discovery-stage association signals and additional markers indirectly associated with bicuspid aortic valve, were genotyped in a replication cohort that comprised 895 Caucasian cases and 1483 controls. RESULTS: Although none of the association signals were consistent across series, the involvement of HMCN2 in calcium metabolism and valve degeneration caused by calcium deposit, and a nominal but not genome-wide significant association, supported it as an interesting gene for follow-up studies on the genetic susceptibility to bicuspid aortic valve. CONCLUSIONS: The absence of a genome-wide significant association signal shows this valvular malformation may be more genetically complex than previously believed. Exhaustive phenotypic characterization, even larger datasets, and collaborative efforts are needed to detect the combination of rare variants conferring risk which, along with specific environmental factors, could be causing the development of this disease.

Postmortem genetic testing should be recommended in sudden cardiac death cases due to thoracic aortic dissection.

BACKGROUND: Acute thoracic aortic dissections and ruptures, the main life-threatening complications of the corresponding aneurysms, are an important cause of sudden cardiac death. Despite the usefulness of the molecular diagnosis of these conditions in the clinical setting, the corresponding forensic field remains largely unexplored. The main goal of this study was to explore and validate a new massive parallel sequencing candidate gene​ assay as a diagnostic tool for acute thoracic aortic dissection autopsy cases. MATERIALS AND METHODS: Massive parallel sequencing of 22 thoracic aortic disease candidate genes performed in 17 cases of thoracic aortic dissection using AmpliSeq and Ion Proton technologies. Genetic variants were filtered by location, type, and frequency at the Exome Aggregation Consortium and an internal database and further classified based on the American College of Medical Genetics and Genomics (ACMG) recommendations published in 2015. All prioritized results were confirmed by traditional sequencing. RESULTS: From the total of 10 potentially pathogenic genetic variants identified in 7 out of the 17 initial samples, 2 of them were further classified as pathogenic, 2 as likely pathogenic, 1 as possibly benign, and the remaining 5 as variants of uncertain significance, reaching a molecular autopsy yield of 23%, approximately. CONCLUSIONS: This massive parallel sequencing candidate gene approach proved useful for the molecular autopsy of aortic dissection sudden cardiac death cases and should therefore be progressively incorporated into the forensic field, being especially beneficial for the anticipated diagnosis and risk stratification of any other family member at risk of developing the same condition.

PRKG1 and genetic diagnosis of early-onset thoracic aortic disease.

BACKGROUND: The 20% of thoracic aortic aneurysms and dissections independent from the main connective tissue syndromes and expected to be familial has gained importance over the past years. The more frequent pattern of inheritance of these nonsyndromic cases is autosomal dominant with incomplete penetrance and variable expression. Although many candidate genes exist, unresolved familial cases suggest still unravelled genetic variation. The main purpose of this study was to establish the genetic diagnosis of one of those. MATERIALS AND METHODS: To begin with, we applied a candidate gene approach based on both traditional and a customized massive parallel sequencing panel, followed by Illumina HiSeq 2000 whole exome sequencing of four family members affected by early-onset thoracic aortic disease and two unaffected relatives. We prioritized whole exome sequencing results based on variant location, type and frequency in general population databases and performed segregation analysis in 14 family members using traditional sequencing. RESULTS: After the negative results we obtained with candidate gene approaches, the analysis and prioritization of whole exome sequencing results brought out the heterozygote c.530G>A:p.Arg177Gln PRKG1 variant (NM_001098512), located in one of the aortic smooth muscle cell contractile apparatus genes. This candidate variant segregated with thoracic aortic disease, as it was present in seven affected and absent in five unaffected family members, further supporting its causality. CONCLUSIONS: This was the second time PRKG1 was associated with thoracic aortic disease, highlighting and reaffirming it as a strong candidate for gene-based diagnosis of nonsyndromic early-onset cases.

Whole exome sequencing for the identification of a new mutation in TGFB2 involved in a familial case of non-syndromic aortic disease.

BACKGROUND: Non-syndromic aortic disease (NSAD) is a frequently asymptomatic but potentially lethal disease characterised by familial cases of thoracic aortic aneurysms and dissections. This monogenic but genetically heterogeneous condition is primarily inherited as an autosomal dominant disorder with low penetrance and variable expression. Mutations in ACTA2, TGFBR1, TGFBR2, MYH11, SMAD3, MYLK, and FBN1 genes have been described but still, there are many unresolved familial cases. METHODS: The whole exome of two distantly related and affected members of a Spanish family with multiple cases of NSAD was analysed through 5500 SOLiD(™) System for the identification of shared and putative pathogenic variants. RESULTS: A new mutation termed c.C1042T:p.R348C (NM_001135599.2) was identified in TGFB2, a gene located in an evolutionary highly conserved region (Chr1: 218,519,577-218,617,961) that has been recently connected to this disease. The analysis of other family members using capillary sequencing confirmed cosegregation of the mutation with the disease and its incomplete penetrance. CONCLUSIONS: The repeated implication of TGFB2 in the development of thoracic aortic aneurysms and dissections suggests that this gene should be considered during genetic diagnosis of this disease. An accurate diagnosis of affected individuals and additional family members at risk allows for a personalised and more efficient gene-based follow-up and treatment. Finally, the reiterative presence of common musculoskeletal and craniofacial additional features in patients with TGFB2 mutations suggests the existence of a new yet undefined connective tissue syndrome responsible for not only aortic dilation, but also for the other extracardiac alterations present in the affected patients.