Successes and challenges of using whole exome sequencing to identify novel genes underlying an inherited predisposition for thoracic aortic aneurysms and acute aortic dissections

Abstract

Thoracic aortic aneurysms involving the aortic root and/or ascending aorta can lead to acute aortic dissections. Approximately 20% of patients with thoracic aortic aneurysms and dissections (TAAD) have a family history of the disease, referred to as familial TAAD (FTAAD) that can be inherited in an autosomal dominant manner with variable expression with respect to disease presentation, age of onset and associated features. Whole exome sequencing (WES) has been used to identify causative mutations in novel genes for TAAD. The strategy used to reduce the large number of rare variants identified using WES is to sequence distant relatives with TAAD and filter for heterozygous rare variants that are shared between the relatives, predicted to disrupt protein function and segregate with the TAAD phenotype in other family members. Putative genes are validated by identifying additional families with a causative mutation in the genes. This approach has successfully identified novel genes for FTAAD.

Fig. 1

Pedigrees of families TAA288 (TGFB2 mutation), TAA216 (PRKG1 mutation), TAA549 (SMAD3 mutation), and TAA059 with TAAD and additional clinical phenotypes, such as abdominal aortic aneurysm, other arterial aneurysms, and bicuspid aortic valve. Squares represent males and circles represent females. The symbols represent different diagnoses as shown in the legend. The age at diagnosis (“dx”) is shown in years and “d” indicates age at death. Circled symbols indicate individuals whose DNA was used in WES assay.

Fig. 2

Strategy of filtering WES data to decrease the number of candidate gene variants in a family. MAF- minor allele frequency; NHLBI GO ESP- National Heart Lung and Blood Institute GO Exome Sequencing Project.

Fig. 3

The number of candidate rare variants remaining after filtering is dependent on the degree of relatedness between affected family members selected for WES. The x-axis indicates the degree of relatedness among affected individuals who were selected for WES and the y-axis indicates the number of candidate gene variants remaining in each family after the filtering strategy is completed.

Fig. 4

Whole genome linkage analysis using DNA from large FTAAD families reduces the number of candidate gene variants identified. The x-axis indicates the families used for WES and the y-axis indicates the number of candidate gene variants identified. Open bars indicate the number of candidate variants identified by WES; and filled bars indicate the number of candidate variants identified by WES and located within putative disease loci identified by linkage analysis.