Pearls & Oy-sters: Whole-Genome Sequencing in Critically Ill Neurologic Patient Leads to Diagnosis With Treatment Implications.

Many adult patients with a history of seizures and global developmental delay do not have an identified etiology for their epilepsy. Rapid whole-genome sequencing (rWGS) can be used to identify a genetic etiology in critically ill patients to provide actionable interventions. In this case, a 27-year-old patient with a history of epilepsy, global developmental delay, and intellectual disability presented with altered mental status and new abnormal movements. The patient acutely declined over the course of 24-48 hours of presentation, including nonconvulsive status epilepticus leading to intubation for airway protection, 2 episodes of ventricular tachycardia requiring synchronized cardioversion, and 1 episode of supraventricular tachycardia. The patient was found to be in metabolic crisis. Metabolic workup and rapid whole-genome sequencing were sent. Patient was treated with 10% dextrose in normal saline and a mitochondrial cocktail. She received treatment with ammonia scavengers and hemodialysis with resolution of metabolic crisis. rWGS found a homozygous pathogenic variant in TANGO2 and a de novo pathogenic variant in KCNQ1, ultimately leading to the creation of a metabolic emergency protocol and implantable cardioverter defibrillator placement. This case highlights the use of rWGS in an acutely ill patient leading to actionable interventions. It also highlights the utility and importance of genetic sequencing in reevaluation of adult neurologic patients.

Necrotizing Enterocolitis following Onasemnogene Abeparvovec for Spinal Muscular Atrophy: A Case Series.

Onasemnogene abeparvovec treats spinal muscular atrophy by delivering a functional SMN1 gene. Necrotizing enterocolitis typically occurs in preterm infants. We report 2 term infants diagnosed with spinal muscular atrophy who presented with necrotizing enterocolitis after onasemnogene abeparvovec infusion. We discuss potential etiologies and propose monitoring for necrotizing enterocolitis after onasemnogene abeparvovec therapy.

Exome Sequencing Implicates Impaired GABA Signaling and Neuronal Ion Transport in Trigeminal Neuralgia.

Trigeminal neuralgia (TN) is a common, debilitating neuropathic face pain syndrome often resistant to therapy. The familial clustering of TN cases suggests that genetic factors play a role in disease pathogenesis. However, no unbiased, large-scale genomic study of TN has been performed to date. Analysis of 290 whole exome-sequenced TN probands, including 20 multiplex kindreds and 70 parent-offspring trios, revealed enrichment of rare, damaging variants in GABA receptor-binding genes in cases. Mice engineered with a TN-associated de novo mutation (p.Cys188Trp) in the GABAA receptor Cl- channel γ-1 subunit (GABRG1) exhibited trigeminal mechanical allodynia and face pain behavior. Other TN probands harbored rare damaging variants in Na+ and Ca+ channels, including a significant variant burden in the α-1H subunit of the voltage-gated Ca2+ channel Cav3.2 (CACNA1H). These results provide exome-level insight into TN and implicate genetically encoded impairment of GABA signaling and neuronal ion transport in TN pathogenesis.

EphrinB2-EphB4-RASA1 Signaling in Human Cerebrovascular Development and Disease.

Recent whole exome sequencing studies in humans have provided novel insight into the importance of the ephrinB2-EphB4-RASA1 signaling axis in cerebrovascular development, corroborating and extending previous work in model systems. Here, we aim to review the human cerebrovascular phenotypes associated with ephrinB2-EphB4-RASA1 mutations, including those recently discovered in Vein of Galen malformation: the most common and severe brain arteriovenous malformation in neonates. We will also discuss emerging paradigms of the molecular and cellular pathophysiology of disease-causing ephrinB2-EphB4-RASA1 mutations, including the potential role of somatic mosaicism. These observations have potential diagnostic and therapeutic implications for patients with rare congenital cerebrovascular diseases and their families.

Mutations in Chromatin Modifier and Ephrin Signaling Genes in Vein of Galen Malformation.

Normal vascular development includes the formation and specification of arteries, veins, and intervening capillaries. Vein of Galen malformations (VOGMs) are among the most common and severe neonatal brain arterio-venous malformations, shunting arterial blood into the brain's deep venous system through aberrant direct connections. Exome sequencing of 55 VOGM probands, including 52 parent-offspring trios, revealed enrichment of rare damaging de novo mutations in chromatin modifier genes that play essential roles in brain and vascular development. Other VOGM probands harbored rare inherited damaging mutations in Ephrin signaling genes, including a genome-wide significant mutation burden in EPHB4. Inherited mutations showed incomplete penetrance and variable expressivity, with mutation carriers often exhibiting cutaneous vascular abnormalities, suggesting a two-hit mechanism. The identified mutations collectively account for ∼30% of studied VOGM cases. These findings provide insight into disease biology and may have clinical implications for risk assessment.

De Novo Mutation in Genes Regulating Neural Stem Cell Fate in Human Congenital Hydrocephalus.

Congenital hydrocephalus (CH), featuring markedly enlarged brain ventricles, is thought to arise from failed cerebrospinal fluid (CSF) homeostasis and is treated with lifelong surgical CSF shunting with substantial morbidity. CH pathogenesis is poorly understood. Exome sequencing of 125 CH trios and 52 additional probands identified three genes with significant burden of rare damaging de novo or transmitted mutations: TRIM71 (p = 2.15 × 10-7), SMARCC1 (p = 8.15 × 10-10), and PTCH1 (p = 1.06 × 10-6). Additionally, two de novo duplications were identified at the SHH locus, encoding the PTCH1 ligand (p = 1.2 × 10-4). Together, these probands account for ∼10% of studied cases. Strikingly, all four genes are required for neural tube development and regulate ventricular zone neural stem cell fate. These results implicate impaired neurogenesis (rather than active CSF accumulation) in the pathogenesis of a subset of CH patients, with potential diagnostic, prognostic, and therapeutic ramifications.

De novo MYH9 mutation in congenital scalp hemangioma.

Congenital hemangiomas are tumor-like vascular malformations with poorly understood pathogenesis. We report the case of a neonate with a massive congenital scalp hemangioma that required urgent neurosurgical removal on the second day of life because of concern for high-flow arteriovenous shunting. Exome sequencing identified a rare damaging de novo germline mutation in MYH9 (c.5308C>T, p.[Arg1770Cys]), encoding the MYH9 nonmuscle myosin IIA. MYH9 has a probability of loss-of-function intolerance (pLI) score of >0.99 and is highly intolerant to missense variation (z score = 5.59). The p.(Arg1770Cys) mutation substitutes an evolutionarily conserved amino acid in the protein's critical myosin tail domain and is predicted to be highly deleterious by SIFT, PolyPhen-2, MetaSVM, and CADD. MYH9 is a known regulator of cytokinesis, VEGF-regulated angiogenesis, and p53-dependent tumorigenesis. These findings reveal a novel association of germline de novo MYH9 mutation with congenital hemangioma.

Human genetics and molecular mechanisms of vein of Galen malformation.

Vein of Galen malformations (VOGMs) are rare developmental cerebrovascular lesions characterized by fistulas between the choroidal circulation and the median prosencephalic vein. Although the treatment of VOGMs has greatly benefited from advances in endovascular therapy, including technical innovation in interventional neuroradiology, many patients are recalcitrant to procedural intervention or lack accessibility to specialized care centers, highlighting the need for improved screening, diagnostics, and therapeutics. A fundamental obstacle to identifying novel targets is the limited understanding of VOGM molecular pathophysiology, including its human genetics, and the lack of an adequate VOGM animal model. Herein, the known human mutations associated with VOGMs are reviewed to provide a framework for future gene discovery. Gene mutations have been identified in 2 Mendelian syndromes of which VOGM is an infrequent but associated phenotype: capillary malformation-arteriovenous malformation syndrome ( RASA1) and hereditary hemorrhagic telangiectasia ( ENG and ACVRL1). However, these mutations probably represent only a small fraction of all VOGM cases. Traditional genetic approaches have been limited in their ability to identify additional causative genes for VOGM because kindreds are rare, limited in patient number, and/or seem to have sporadic inheritance patterns, attributable in part to incomplete penetrance and phenotypic variability. The authors hypothesize that the apparent sporadic occurrence of VOGM may frequently be attributable to de novo mutation or incomplete penetrance of rare transmitted variants. Collaboration among treating physicians, patients' families, and investigators using next-generation sequencing could lead to the discovery of novel genes for VOGM. This could improve the understanding of normal vascular biology, elucidate the pathogenesis of VOGM and possibly other more common arteriovenous malformation subtypes, and pave the way for advances in the diagnosis and treatment of patients with VOGM.

Incidence, clinical features, and treatment of familial moyamoya in pediatric patients: a single-institution series.

OBJECTIVE Limited data exist on familial moyamoya in children. The purpose of this study was to characterize presentation and outcomes of pediatric moyamoya patients who have relatives diagnosed with moyamoya. METHODS The authors performed a single-institution retrospective analysis of a case series including all surgically treated children with moyamoya with first- or second-degree relatives with moyamoya. Clinical and radiographic characteristics were analyzed, along with surgical outcomes. RESULTS A total of 537 patients underwent surgery for moyamoya during the study period. Eighteen of those patients (3.4% of the total series) had moyamoya and a family history of moyamoya and were included in this study. Of these 18 patients, 14 were non-twin siblings, and the remaining 4 represented 2 pairs of identical (affected) twins. The presentation was predominantly ischemic (72%), but 4 patients (33%) were asymptomatic when they were found to have moyamoya. Bilateral disease was present in 13 patients (72%). Radiographic stroke prevalence (67%), Suzuki grade (3.3), and angiographic findings were comparable to findings in nonfamilial moyamoya patients. Thirty revascularization procedures were performed, with a 3.3% operative stroke rate per hemisphere and no new strokes in an average follow-up period of 4.5 years. CONCLUSIONS In a North American surgical series, familial moyamoya existed in 3.4% of cases, and was distinguished by manifesting in a broad range of ethnic groups, with a higher proportion of male patients and increased rates of asymptomatic and unilateral disease in comparison to nonfamilial moyamoya. Screening indications remain controversial and the current data are used to suggest guidelines. Surgical therapy is warranted, effective, and durable in these patients, but patients should be carefully selected.

Novel determinants of mammalian primary microRNA processing revealed by systematic evaluation of hairpin-containing transcripts and human genetic variation.

Mature microRNAs (miRNAs) are processed from hairpin-containing primary miRNAs (pri-miRNAs). However, rules that distinguish pri-miRNAs from other hairpin-containing transcripts in the genome are incompletely understood. By developing a computational pipeline to systematically evaluate 30 structural and sequence features of mammalian RNA hairpins, we report several new rules that are preferentially utilized in miRNA hairpins and govern efficient pri-miRNA processing. We propose that a hairpin stem length of 36 ± 3 nt is optimal for pri-miRNA processing. We identify two bulge-depleted regions on the miRNA stem, located ∼16-21 nt and ∼28-32 nt from the base of the stem, that are less tolerant of unpaired bases. We further show that the CNNC primary sequence motif selectively enhances the processing of optimal-length hairpins. We predict that a small but significant fraction of human single-nucleotide polymorphisms (SNPs) alter pri-miRNA processing, and confirm several predictions experimentally including a disease-causing mutation. Our study enhances the rules governing mammalian pri-miRNA processing and suggests a diverse impact of human genetic variation on miRNA biogenesis.

Cerebrospinal fluid hypersecretion in pediatric hydrocephalus.

Hydrocephalus, despite its heterogeneous causes, is ultimately a disease of disordered CSF homeostasis that results in pathological expansion of the cerebral ventricles. Our current understanding of the pathophysiology of hydrocephalus is inadequate but evolving. Over this past century, the majority of hydrocephalus cases has been explained by functional or anatomical obstructions to bulk CSF flow. More recently, hydrodynamic models of hydrocephalus have emphasized the role of abnormal intracranial pulsations in disease pathogenesis. Here, the authors review the molecular mechanisms of CSF secretion by the choroid plexus epithelium, the most efficient and actively secreting epithelium in the human body, and provide experimental and clinical evidence for the role of increased CSF production in hydrocephalus. Although the choroid plexus epithelium might have only an indirect influence on the pathogenesis of many types of pediatric hydrocephalus, the ability to modify CSF secretion with drugs newer than acetazolamide or furosemide would be an invaluable component of future therapies to alleviate permanent shunt dependence. Investigation into the human genetics of developmental hydrocephalus and choroid plexus hyperplasia, and the molecular physiology of the ion channels and transporters responsible for CSF secretion, might yield novel targets that could be exploited for pharmacotherapeutic intervention.

Macro fat and micro fat: insulin sensitivity and gender dependent response of adipose tissue to isocaloric diet change.

The adipose cell-size distribution is a quantitative characterization of adipose tissue morphology. At a population level, the adipose cell-size distribution is insulin-sensitivity dependent, and the observed correlation between obesity and insulin resistance is believed to play a key role in the metabolic syndrome. Changes in fat mass can be induced by altered energy intake or even diet composition. These macroscopic changes must manifest themselves as dynamic adipose cell-size distribution alterations at the microscopic level. The dynamic relationship between these 2 independent measurements of body fat is unknown. In this study, we investigate adipose tissue dynamics in response to various isocaloric diet compositions, comparing gender- and insulin sensitivity-dependent differences. A body composition model is used to predict fat mass changes in response to changes in diet composition for 28 individuals, separated into 4 subgroups according to gender and insulin sensitivity/resistance. Adipose cell-size distribution changes in each individual are simulated with a dynamic model and parameters corresponding to lipid turnover and cell growth rates are determined for each subgroup to match the relative change of fat mass for each diet composition, respectively. We find that adipose cell-size dynamics are associated with different modulations dependent on gender and insulin resistance. Larger turnover and growth/shrinkage rates in insulin resistant individuals suggest they may be more sensitive to changes in energy intake and diet composition than insulin sensitive subjects. The different cell-size distribution changes of adipose cells of various sizes in different subject groups further suggest distinct modulations of adipose cell dynamics.