Introduction: Brain arteriovenous malformations are an abnormal connection between arteries and veins that can result in hemorrhagic stroke. They occur as part of a syndrome affecting multiple organ systems, namely hereditary hemorrhagic telangiectasia, or sporadically. While their genetic basis in HHT is mapped to known germline mutations in ACVRL1, ENG, and SMAD4, little is known about the sporadic lesions. Information may be gained about the sporadic condition from patients that develop rare, recurrent lesions after treatment. These patients are suspected to have a strong genetic influence.
Methods: We performed whole exome sequencing [Illumina HiSeq2000, Nextera Rapid Capture Exome kit with bait/target size of 38Mb, San Diego, CA USA] on 16-year-old patient with a brain arteriovenous malformation that recurred in the same location following complete surgical resection two years prior. DNA was extracted from the patient’s recurrent AVM and peripheral blood. Variants were called with VarScan version 2.4.0.
Results: A rare heterozygous germline mutation was detected at Chr13:37439827,G,A (GRCh37), and was present in both tissue and blood. Sanger sequencing was used to confirm the mutation. Immunofluorescence of the AVM tissue identified a corresponding decrease of SMAD9 expression as a result of the stop codon. Intriguingly, levels of phosphorylated-SMAD4 were also decreased, a downstream common effector in the BMP signaling pathway. Zebrafish (Tg Flk:eGFP) morpholino splice site and translation blocking knockdown of SMAD9 resulted in severe circulation defects.
Conclusions: This is the first report of a causative mutation in sporadic brain AVM. Next generation sequencing has the potential to identify the causative genetic pathways responsible for brain vascular malformations.
Patient Care: Understanding the genetic causes for brain vascular malformations has the potential to lead to novel therapeutics.
Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the known genes implicated in syndromic brain AVM [hereditary hemorrhagic telangiectasia]. 2) Appreciate the utility of next generation sequencing to detect rare variants in vascular malformations 3) Identify methods to functionally validate genetic variants (measure phenotypic effect).
References: Walcott, Brian P., et al. "Molecular, Cellular, and Genetic Determinants of Sporadic Brain Arteriovenous Malformations." Neurosurgery 63 (2016): 37-42.
Walcott, Brian P. "BMP signaling modulation attenuates cerebral arteriovenous malformation formation in a vertebrate model." Journal of Cerebral Blood Flow & Metabolism 34.10 (2014): 1688-1694.