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. First, using a technique called quantitative trait locus analysis, we identified different regions of the mouse genome where differences in genetic background impact the degree of hypertension and vascular narrowing in Eln+/- mice. Subsequent work has identified distinct genetic modifiers from under two of those peaks (Ren1 and Ncf1) with an additional genomic region on chromosome 2 near the Fbn1 and Jag1 genes. With the identification of these modifiers, further study into the mechanism of action and potential therapeutic value can be undertaken. Data acquired this year revealed that NCF1, a component of the NADPH oxidase system, is important for generating reactive oxygen species (ROS) in elastin insufficient vessels. ROS production influences reactivity in Eln+/- vessels contributing to the high blood pressure and vascular stiffness observed in these patients and animals. Inhibition of ROS production using chemical or genetic modifications, decreases blood pressure and stiffness. Secondly, we have acquired tissue samples from individuals with WS that have severe arteriopathy and from those with more mild cardiovascular features. By growing those tissues and studying the differences between the two groups (gene expression, rate of proliferation, etc), genes and pathways can be identified that differentiate the two. Such work can be done in the fibroblasts themselves or by turning the cells into smooth muscle cells by the production of induced pluripotent stem cells (IPSC). To date, we have generated several IPSC lines and have successfully derived smooth muscle cells that deposit elastin. We have learned that elastin deposition by these lines requires expression of additional elastic fiber assembly proteins, such as Fbln4, Fbln5, and Lox. We are currently characterizing smooth muscle cell subtypes from our IPS lines optimally produce and deposit elastin. Finally, we are looking at the association of rare and common genomic variants with disease severity in WS patients. Toward this end, we have collected questionnaire data, medical records and DNA on more than 180 individuals with Williams Beuren syndrome. We performed exome sequencing and began to compare genetic variants between those with mild disease and those with a more severe phenotype. To optimize power, we focused our analysis on candidate genes and pathways identified from information in the literature or from our animal and cell studies. Our first manuscript looking at variation in genes that impact social behavioral features in WBS was published this year. We are also completing an analysis on variation in cardiovascular disease that rules out the remaining elastin allele as well as variation within the WBS locus (other than NCF1 copy number) as major contributors to SVAS or hypertension. Further work in this area has identified genes and pathways outside of the WS locus, including the genes expressed as part of the matrisome, VEGF signaling, and adaptive immunity that influence the severity of vascular disease in WBS. Subsequent work in animal models has confirmed a role for the adaptive immune system in disease modification. We have now acquired additional WBS simples that will be evaluated by genome sequencing to replicate our initial studies and extend these studies into modifiers outside of the coding sequence. Taken together, these three complimentary projects will allow us to identify important pathways that interact with elastin insufficiency to produce clinical disease. The identification of such pathways may direct us to potential therapies to increase elastin production and 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.
| Kopp, Nathan D; Parrish, Phoebe C R; Lugo, Michael et al. (2018) Exome sequencing of 85 Williams-Beuren syndrome cases rules out coding variation as a major contributor to remaining variance in social behavior. Mol Genet Genomic Med 6:749-765 |
| Duque Lasio, Maria Laura; Kozel, Beth A (2018) Elastin-driven genetic diseases. Matrix Biol : |
| Baldridge, Dustin; Heeley, Jennifer; Vineyard, Marisa et al. (2017) The Exome Clinic and the role of medical genetics expertise in the interpretation of exome sequencing results. Genet Med 19:1040-1048 |
