Identification of Genetic Modifiers in HHT

 

Whitney Wooderchak-Donahue, PhD, is an Adjunct Assistant Professor, Department of Pathology at the University of Utah and a Research Investigator at ARUP Laboratories working under the direction of Dr. Pinar Bayrak-Toydemir.  In 2015, Dr. Wooderchak-Donahue was awarded a $30,000 Young Investigator Grant by Cure HHT.

 

 

Proposed Research Summary

Mutations in ENG, ACVRL1, and SMAD4 cause HHT. However, this genetic heterogeneity does not explain the extremely variable clinical symptoms routinely seen with HHT families suggesting that genetic modifiers influence phenotypic variation. Dr. Wooderchak-Donahue’s project focused on identifying additional genetic modifiers in HHT.

Dr. Wooderchak-Donahue focused on identifying additional genetic modifiers and causative mutations in HHT. She hypothesized that the phenotypic variability of HHT is caused by mutations in additional genes or genetic modifiers critical to vascular development. She tested her hypothesis by:

  1. Aim 1 – Identify genetic modifiers of the HHT phenotype in members of the same family who have an ENG or ACVRL1 mutation and
  2. Aim 2 – Elucidate the genetic basis of vascular malformations in HHT families and patients who do not have a known ENG, ACVRL1 or SMAD4 mutation.

These discoveries will help us understand the nature of genetic modifiers in HHT and will lead to better diagnostics for HHT patients with the addition of new genes to the HHT NGS panel, better genetic counseling and may ultimately lead to the development of new therapeutics for HHT.

 

Research Study Update

Aim 1 – Dr. Wooderchak-Donahue collected ~100 paired RNA and DNA samples from HHT patients who have a known ENG or ACVRL1 mutation. Many are from affected family members from two large extended pedigrees with an ACVRL1 mutation. In one family, the Utah HHT center has seen >120 affected family members with an ACVRL1 missense mutation spanning eight generations including relatives as distant as 13th degree. The second family with 43 affected individuals, some with up to 12 degrees of separation, has an ACVRL1 exon 10 deletion. These families include individuals with known brain, lung, and liver AVMs, and epistaxis ranging from mild to severe. Access to RNA from distant relatives will facilitate the identification of genetic modifiers that may influence the development of arteriovenous malformations (AVMs) in certain family members versus others who share the same ACVRL1 mutation.

Aim 2 – Dr. Wooderchak-Donahue collected data from >100 exomes and 37 genomes from HHT patients from fourteen kindreds who do not have an identifiable ENG, ACVRL1, or SMAD4 mutation. Genome data is currently being analyzed and compared to previously collected exome data using Ingenuity Variant Analysis software. In addition to DNA, RNA was obtained from key individuals with and without AVMs from seven of these families in which exome and/or genome data is already available. RNA extracted from the peripheral blood of 9 patients from this cohort underwent successful transcriptome preparation and next generation sequencing. Analysis is currently underway to better understand the functional consequences of potential disease causing variants identified such as splicing defects and novel transcripts.

Future plans – The goal is to use the results from this pilot study as preliminary data for a large, competitive Department of Defense (DOD) grant application to provide evidence for the feasibility of RNA transcriptome sequencing in HHT patients for the detection of new genes and genetic modifiers in HHT. The DOD grant will be led by Dr. Pinar Bayrak-Toydemir and Dr. Kevin Whitehead from the University of Utah as lead principal investigators.

 

Lay Summary