Redefining the Etiologic Landscape of Cerebellar Malformations

Cerebellar malformations are diverse congenital anomalies frequently associated with developmental disability. Although genetic and prenatal non-genetic causes have been described, no systematic analysis has been performed. Here, we present a large-exome sequencing study of Dandy-Walker malformation (DWM) and cerebellar hypoplasia (CBLH). We performed exome sequencing in 282 individuals from 100 families with DWM or CBLH, and we established a molecular diagnosis in 36 of 100 families, with a significantly higher yield for CBLH (51%) than for DWM (16%). The 41 variants impact 27 neurodevelopmental-disorder-associated genes, thus demonstrating that CBLH and DWM are often features of monogenic neurodevelopmental disorders. Though only seven monogenic causes (19%) were identified in more than one individual, neuroimaging review of 131 additional individuals confirmed cerebellar abnormalities in 23 of 27 genetic disorders (85%). Prenatal risk factors were frequently found among individuals without a genetic diagnosis (30 of 64 individuals [47%]). Single-cell RNA sequencing of prenatal human cerebellar tissue revealed gene enrichment in neuronal and vascular cell types; this suggests that defective vasculogenesis may disrupt cerebellar development. Further, de novo gain-of-function variants in PDGFRB, a tyrosine kinase receptor essential for vascular progenitor signaling, were associated with CBLH, and this discovery links genetic and non-genetic etiologies. Our results suggest that genetic defects impact specific cerebellar cell types and implicate abnormal vascular development as a mechanism for cerebellar malformations. We also confirmed a major contribution for non-genetic prenatal factors in individuals with cerebellar abnormalities, substantially influencing diagnostic evaluation and counseling regarding recurrence risk and prognosis.

Abstract TP503: Screening Algorithm for Hereditary Hemorrhagic Telangiectasia in Pediatric Brain AVM

Background: Hereditary Hemorrhagic Telangiectasia (HHT) is a rare cause of familial arteriovenous malformation (AVM) which may present symptomatically in the brain, spine, pulmonary, or hepatic circulation. Symptoms and signs of HHT - including epistaxis, GI bleeding, and cutaneous telangiectasia - may not be manifest at the time of AVM diagnosis. Natural history studies suggesting a more benign course for HHT-associated AVM compared to sporadic AVM may reflect a sampling bias if the true frequency of HHT is under-estimated. In this study, we report our experience with HHT screening in a population with pediatric brain AVM.

Methods: Patients followed in the multidisciplinary Cincinnati Children’s Hospital Cerebrovascular Center are interviewed by a genetics counselor after identification of a brain AVM. A comprehensive medical and family history are collected and patients are offered screening for HHT using a 5 gene panel (Ambry Genetics: ACVRL1, ENG, SMAD4, RASA1, GDF2). Further testing with bubble echocardiogram and skin examination is offered to identify clinical criteria for HHT per Curacao criteria.

Results: Brain AVM was identified in 12 patients followed in our center with age range 5 weeks to 17 years at AVM diagnosis. Recurrent epistaxis was present in 6 (50%) of our patients. Family history is negative for HHT in all cases although 75% of patients had at least 1 first degree relative with recurrent epistaxis. Additional diagnostics were completed in 10 of 12 patients, including genetic testing in 9 individuals. No pathogenic mutations were identified in this small cohort but 2 patients showed variants of unknown significance in ENG (p.R3C and p.E41K). Of the 10 patients who completed additional screening for HHT, 2 met criteria for definite HHT (ages 3 and 17) and 2 for possible HHT (ages 2 and 10).

Conclusions: In our cohort of pediatric brain AVM patients, 33% met criteria for possible or definite HHT. The clinical symptoms and signs of HHT emerge over time. Using a standard diagnostic algorithm for reassessment of Curacao criteria may help facilitate correct and timely diagnosis. For cases confirmed with definite HHT, genetic counseling and gene testing should be considered.