Modifiers of elastin arteriopathy

National Heart, Lung, And Blood Institute

Investigators

Linked publications, trials & patents

Abstract

To characterize genetic variation that impacts the severity of blood vessel disease in patients with elastin insufficiency and Williams syndrome, we are using a combination of approaches. Our previous modifier studies in human identified new pathways, such as the extracellular matrix, adaptive immune system, and g protein signaling that might modify phenotypic outcome for patients with WS. In the past year, we have grown this work by collaborating with scientists and physicians in Italy, Canada and the United States to perform whole genome sequencing on more than 450 individuals with WS. We are continuing to look at the association of rare and common genomic events in 3 levels (single nucleotide variants (SNVs), structural variants (SV), copy number variants (CNVs)) with vascular disease severity in people with WS. To date, we have performed alignment and joint variant calling using GATK on the NIH biowulf cluster, and imputed/phased single nucleotide variants using the TOPMED imputation server. We have completed SNV and CNV calling are beginning work on SV analysis. In the modifier project, we focused on establishing a framework for identifying pathways associated with extreme outcomes for rare disease studies, including WBS, where smaller datasets are the rule. Using the new framework in the WS cohort, we identified pathways with increased pathogenic variant frequency in people with surgical vs. no stenosis. We have confirmed the pathways first identified in our exome study, including the matrisome, immune and lipid metabolism pathways. In addition, with the improved power from the larger cohort, we expanded the study to investigate rarer variants and saw an enrichment for pathways impacting the cell cycle and estrogen responsiveness. We have also identified several genes, including PCSK9 and ILR, that have been targeted from a therapeutic standpoint in other common and rare vascular diseases. This manuscript is now complete, and we expect to submit soon. In addition, we published an editorial describing how common and rare variants synergize with the primary disease driving variant to influence outcomes. (Luperchio et al, Curr Opin Genet Dev.). Although most of our effort to date has focused on coding variants, we have just begun to explore the impact of non-coding variation in elastin and other extracellular matrix genes on disease features. Additionally, as part of our CNV analysis, we aimed to define the total burden of copy number change in people with WS by comparing CNV frequency in people with WS vs controls. We have a set of secondary deletions, present at a higher rate in individuals with WS that we are now validating using a variety of methods (chromosomal microarray and the BioNano optical mapping system). Such efforts may allow us to call WS deletion boundaries with greater certainty (a task that is currently difficult due to the redundancy of the genome in those areas). In that way, deletion size can be better assessed for its impact on phenotypic outcomes. Given that two studies have now identified an impact for variants within the adaptive immune system, we were keen model this scenario in an organism. Our past work focused on the Eln+/- mouse. Unfortunately, the Eln+/- mouse does not mimic the focal stenosis commonly seen in people with WS, mimicking more the long segment stenosis seen in this population. As such, we have begun work on a new Elnfl/fl model which, when bred to a smooth muscle cre, produces more focal stenosis with a notable inflammatory component. We recently completed breeding of the Rag1-/- mouse, a line that produces no B or T cells) and have shown earlier death in the Elnfl/fl; SMC-cre; Rag1-/-. Additional breeding is underway to create the Elnfl/fl; SMC-cre; IL6R model. Subsequent work will evaluate the mechanism by which the innate and adaptive immune systems may influence disease patterns and viability of the mutant. Also on the mouse side, we have begun investigation of a second mouse line that contains a knock-out mutation in one of the other genes in the WS locus. This gene, Baz1b, is a widely expressed transcription factor thought to predominantly impact cells derived from the neural crest. The knockout mice are born alive but generally die within 24 hours. The heterozygous mice have significantly reduced survival relative to WT mice and slower growth. Efforts aimed determining the cause of sudden death in this line show normal cardiac anatomy in the Baz1b-/- and Baz1b+/- and evidence of worsening ejection fraction with concomitant left ventricular wall changes in the Baz1b+/- (intriguingly work in our human patients with WS has also recently shown evidence of increasing cardiac dysfunction in adults with the condition). There is also a suggestion of decreased pulmonary function, with poor lung aeration in the newborn Baz1b-/- as well as decreased chirping of neonatal Baz1b+/- pups that may suggest difficulties with opening the airway. An abstract on this work was presented at Experimental Biology 2022 and was published in FASEB Journal. We have also begun investigating the impact of combined variation between elastin and Baz1b in this model. Taken together, these complimentary projects will allow us to identify important pathways that interact with elastin insufficiency to alter disease severity. The discovery of modifier pathways may direct us to novel therapies to improve vascular health. Because elastin concentration decreases with age, the lessons learned from these rare disease patients have the potential to provide information regarding genes and pathways that impact blood vessels in aging individuals. In addition to the analyses performed by our laboratory, data collected under the study protocols was used as part of collaborative studies to investigate social behavioral (Lee et al, Transl Psychiatry) and cardiac features (Brink et al, Pediatr Cardiol)of the condition.