Focal malformations of cortical development, including focal cortical dysplasia (FCD) and hemimegalencephaly (HME), are important causes of intractable childhood epilepsy. Using targeted and exome sequencing on DNA from resected brain samples and non-brain samples from 53 patients with FCD or HME, we identified pathogenic germline and mosaic mutations in multiple PI3K/AKT pathway genes in 9 patients, and a likely pathogenic variant in 1 additional patient. Our data confirm the association of DEPDC5 with sporadic FCD but also implicate this gene for the first time in HME. Our findings suggest that modulation of the mTOR pathway may hold promise for malformation-associated epilepsy.

Arteriovenous malformation (AVM) is a fast-flow, congenital vascular anomaly that may arise anywhere in the body. AVMs typically progress, causing destruction of surrounding tissue and, sometimes, cardiac overload. AVMs are difficult to control; they often re-expand after embolization or resection, and pharmacologic therapy is unavailable. We studied extracranial AVMs in order to identify their biological basis. We performed whole-exome sequencing (WES) and whole-genome sequencing (WGS) on AVM tissue from affected individuals. Endothelial cells were separated from non-endothelial cells by immune-affinity purification. We used droplet digital PCR (ddPCR) to confirm mutations found by WES and WGS, to determine whether mutant alleles were enriched in endothelial or non-endothelial cells, and to screen additional AVM specimens. In seven of ten specimens, WES and WGS detected and ddPCR confirmed somatic mutations in mitogen activated protein kinase kinase 1 (MAP2K1), the gene that encodes MAP-extracellular signal-regulated kinase 1 (MEK1). Mutant alleles were enriched in endothelial cells and were not present in blood or saliva. 9 of 15 additional AVM specimens contained mutant MAP2K1 alleles. Mutations were missense or small in-frame deletions that affect amino acid residues within or adjacent to the protein's negative regulatory domain. Several of these mutations have been found in cancers and shown to increase MEK1 activity. In summary, somatic mutations in MAP2K1 are a common cause of extracranial AVM. The likely mechanism is endothelial cell dysfunction due to increased MEK1 activity. MEK1 inhibitors, which are approved to treat several forms of cancer, are potential therapeutic agents for individuals with extracranial AVM.Arteriovenous malformation (AVM) is a congenital vascular anomaly, comprised of abnormal connections between arteries and veins that are missing normal high-resistance capillary beds (Figure 1). 1 Sporadic extracranial AVMs are solitary and may be localized or regional. Rapid blood flow is demonstrable by Doppler ultrasonography. Magnetic resonance imaging reveals signal voids consistent with fast-flow, while angiography shows the early filling of draining veins (Figure 1). With time, arterial to venous shunting causes tissue ischemia that leads to pain, ulceration, bleeding, and destruction of adjacent tissues. Treatment for AVM has been discouraging. Embolization and/or resection are often followed by expansion; there are no drug treatments. 2 The purpose of this study was to identify the genetic basis for sporadic, extracranial AVM in an effort to devise a new therapeutic strategy.The Committee on Clinical Investigation at Boston Children's Hospital approved this study and informed consent was obtained from study participants. Ten AVM specimens that had been collected during a clinically indicated procedure, including matched unaffected tissue specimens from three of the study participants, had DNA extracted using the DNeasy Blood & Tissue Kit (QIAGEN); saliva DNA was extracted using the pr...

Background A somatic mutation in GNAQ (c.548G>A;p.R183Q), encoding Gαq, has been found in syndromic and sporadic capillary malformation tissue. However, the specific cell type(s) containing the mutation is unknown. The purpose of this study was to determine which cell(s) in capillary malformations have the GNAQ mutation. Methods Human capillary malformation tissue was obtained from 13 patients during a clinically-indicated procedure. Droplet digital PCR (ddPCR), capable of detecting mutant allelic frequencies as low as 0.1%, was used to quantify the abundance of GNAQ mutant cells in capillary malformation tissue. Six specimens were fractionated by fluorescence activated cell sorting (FACS) into hematopoietic, endothelial, perivascular, and stromal cells. The frequency of GNAQ mutant cells in these populations was quantified by ddPCR. Results Eight capillary malformations contained GNAQ p.R183Q mutant cells, 2 lesions had novel GNAQ mutations (p.R183L; p.R183G), and 3 capillary malformations did not have a detectable GNAQ p.R183 mutation. Mutant allelic frequencies ranged from 2% to 11%. Following FACS, the GNAQ mutation was found in the endothelial but not the platelet-derived growth factor receptor-β-positive (PDGFRβ) cell population; mutant allelic frequencies were 3% to 43%. Conculsions Endothelial cells in capillary malformations are enriched for GNAQ mutations and are likely responsible for the pathophysiology underlying capillary malformation.