Modifiers of elastin arteriopathy

National Heart, Lung, And Blood Institute

Investigators

Linked publications & trials

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 describing this work has been submitted and is now in revision. As a follow up, we computed a poly-genic score (PGS) to predict the risk of surgical SVAS in people with WBS using the common variants from the 13 pathways. We are able to achieve prediction accuracy measured by AUC as high as 0.98 between no SVAS and surgical SVAS, and AUC = 0.93 for mild SVAS and surgical SVAS. A replication cohort was sent for sequencing in August of 2023. Once those data are available, we anticipate submitting the work as a research letter to enable rapid integration of the PGS for into clinical care. Given that two studies have now identified an impact for variants within the adaptive immune system, we were keen to model this scenario in an organism. The newer 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 confirmed earlier death in the Elnfl/fl; SMC-cre; Rag1-/-. 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, especially males, have significantly reduced survival relative to WT mice and slower growth; cardiac anatomy is normal and GI tract hyperganglionosis was identified in the mutants. The revision of this work was submitted this week. To further evaluate the mechanism of death and failure to thrive in this model, we performed serial echocardiograms of the mutants. Those efforts identified evidence of decreased ejection fraction with metabolic studies showing differences in fat and lean body mass distribution and electron microscopy showing markedly abnormal mitochondria. Replication of these findings in larger cohorts are needed to better understand how Baz1b gene dosage contributes to the features of WBS but suggest the presence of primary or secondary mitochondrial dysfunction.