Next to present is Dr. Duran, discussing exome sequencing in vein of Galen malformations. Good afternoon. My name is Dan Duran. I'll be briefly discussing the role of molecular characterization in vein of Galen malformations. A bit of background on vein of Galen malformations. This is a very cryptic and misunderstood disease historically. What is the actual ectatic venous structure? That question was not answered until the late 1980s. And what this happens to be is, in fact, a very specific type of developmental arterial venous malformation in which fistulas from choroidal or subependymal arterial networks connect abnormally to the median prosence of phallic vein, which is the embryonic precursor of the vein of Galen proper. So even the name of a disease is improper. This is a misnomer. It sounded initially when we started looking at this problem like the perfect phenotype for study. Clean, sporadic, and I use quotes here deliberately because it's always been mentioned to be a sporadic disease. There's not a lot of cases in which a family has more than one patient with a vein of Galen malformation. Not heavily studied from the genetic standpoint. The only information we had when we started this study was the association of vein of Galen malformation as a sporadic contributor to some not frequent vascular syndromes such as CMAVM syndrome due to RASA1 mutations and HHD due to either ACVRL or ENG mutations. So there was a clear positive genetic information and we were working at a center that has significant experience in dealing with this sort of problem. So it sounded like the perfect plan, right? Well, not really. This was fraught with difficulties. This is a very rare disease. There are no accurate estimates of prevalence of vein of Galen malformation. Due to its rarity. So we had to implement outside-the-box strategies to be able to sequence a significant number of these cases. So as millennials we are, we implemented social media recruitment and we made emphasis on special key collaborations with institutions that do any significant volume of these cases worldwide. Here are some of our collaborating institutions. So through this and in the span of about one and a half years, we were able to collect 50 probands, so basically 50 vein of Galen malformation patients. Most of which were complete with DNA from both parents, which is very important for this type of analysis we do. And this is by far to this point the largest exome sequenced cohort of vein of Galen malformations in the world. I want to touch on the importance of having both parents because what you want to do when you sequence these cases, especially from germline DNAs, to be able to see if the mutations that cause this disease are de novo, happening out of the blue in the patient, or are being transmitted from either of the parents. So we started looking and deconvoluting this information and it's always been called a sporadic disease. So knee jerk was basically to think this is probably due to de novo mutations. And lo and behold, the only case, the only gene that was recurrently mutated in our cohort was KEL, which codes for the highly polymorphic KEL blood antigen. That doesn't seem to contribute to vascular development a lot. So what do you do then besides entering this downward spiral of despair and not realizing that maybe there's other questions? When you hit rock bottom, you start reassessing things and that's exactly what we did. We started looking at transmitted mutations and the possibility that this was in fact not due to de novo mutation, but to collaboration from transmitted mutations coming down from either of the parents. And this is when the first interesting result popped up. We started seeing significant enrichment of mutations in a gene called FB4, which codes for tyrosine kinase, coupled receptor efrin B4, which is a huge player in vascular development. And that was interesting to us because this seemed to be a sporadic disease. So what's going on here? That's when we went back and carefully reinterrogated the structures of these families and we realized that this is in fact not sporadic at all. This is happening in the context of other family members that carry these mutations that are transmitted from either of the parents that have other soft vascular manifestations. Not faint of Galen malformations themselves, but they might have atypical capillary malformations, skin findings, et cetera. Even things so dispersed as atrial septal defects and carriers of some of these efrin B4 mutations. So what this told us was, lo and behold, this is not a sporadic disease and should not be considered a sporadic disease. It's probably a phenotype that is attributable to a syndromic condition. The other interesting thing that we saw is we knew through the literature that efrin B4 is a known interactor of RASA1. If I went back to my first slide, RASA1 is a causal gene for CMAVM syndrome in which people had seen vein of Galen malformations occur in the past. And what we saw is that some of the mutations that we discovered in our patients actually abrogate the interaction between RASA1 and efrin B4. So this seems to align these two genes in a single signaling pathway. Take-home points here are vein of Galen malformations are indeed apparently sporadic but occur as a phenotypic manifestation of a broader syndrome and that they should not be considered isolated lesions. For any of you in the audience that see any number of these cases, please beware of cutaneous manifestations in families with vein of Galen malformation children because they are definite red flags. I'd like to thank the Coli Lab, the Coli Lab members here present, Dr. Cawley, Dr. Lifton, and Dr. Gunal. Thank you.

molecular characterization

vein of Galen malformations

rare disease

FB4 gene mutations

CMAVM syndrome