Novel compound heterozygous frameshift variants in WDR81 associated with congenital hydrocephalus 3 with brain anomalies: First Chinese prenatal case confirms WDR81 involvement

The genetic basis of hydrocephalus: genes, pathways, mechanisms, and global impact

Hydrocephalus (HC) is a heterogenous disease characterized by alterations in cerebrospinal fluid (CSF) dynamics that may cause increased intracranial pressure. HC is a component of a wide array of genetic syndromes as well as a secondary consequence of brain injury (intraventricular hemorrhage (IVH), infection, etc.) that can present across the age spectrum, highlighting the phenotypic heterogeneity of the disease. Surgical treatments include ventricular shunting and endoscopic third ventriculostomy with or without choroid plexus cauterization, both of which are prone to failure, and no effective pharmacologic treatments for HC have been developed. Thus, there is an urgent need to understand the genetic architecture and molecular pathogenesis of HC. Without this knowledge, the development of preventive, diagnostic, and therapeutic measures is impeded. However, the genetics of HC is extraordinarily complex, based on studies of varying size, scope, and rigor. This review serves to provide a comprehensive overview of genes, pathways, mechanisms, and global impact of genetics contributing to all etiologies of HC in humans.

The "microcephalic hydrocephalus" paradox as a paradigm of altered neural stem cell biology

Characterized by enlarged brain ventricles, hydrocephalus is a common neurological disorder classically attributed to a primary defect in cerebrospinal fluid (CSF) homeostasis. Microcephaly ("small head") and hydrocephalus are typically viewed as two mutually exclusive phenomenon, since hydrocephalus is thought of as a fluid "plumbing" disorder leading to CSF accumulation, ventricular dilatation, and resultant macrocephaly. However, some cases of hydrocephalus can be associated with microcephaly. Recent work in the genomics of congenital hydrocephalus (CH) and an improved understanding of the tropism of certain viruses such as Zika and cytomegalovirus are beginning to shed light into the paradox "microcephalic hydrocephalus" by defining prenatal neural stem cells (NSC) as the spatiotemporal "scene of the crime." In some forms of CH and viral brain infections, impaired fetal NSC proliferation leads to decreased neurogenesis, cortical hypoplasia and impaired biomechanical interactions at the CSF-brain interface that collectively engender ventriculomegaly despite an overall and often striking decrease in head circumference. The coexistence of microcephaly and hydrocephalus suggests that these two phenotypes may overlap more than previously appreciated. Continued study of both conditions may be unexpectedly fertile ground for providing new insights into human NSC biology and our understanding of neurodevelopmental disorders.

Genomics of human congenital hydrocephalus

Congenital hydrocephalus (CH), characterized by enlarged brain ventricles, is considered a disease of pathological cerebrospinal fluid (CSF) accumulation and, therefore, treated largely by neurosurgical CSF diversion. The persistence of ventriculomegaly and poor neurodevelopmental outcomes in some post-surgical patients highlights our limited knowledge of disease mechanisms. Recent whole-exome sequencing (WES) studies have shown that rare, damaging de novo and inherited mutations with large effect contribute to ~ 25% of sporadic CH. Interestingly, multiple CH genes are key regulators of neural stem cell growth and differentiation and converge in human transcriptional networks and cell types pertinent to fetal neurogliogenesis. These data implicate genetic disruption of early brain development as the primary pathomechanism in a substantial minority of patients with sporadic CH, shedding new light on human brain development and the pathogenesis of hydrocephalus. These data further suggest WES as a clinical tool with potential to re-classify CH according to a molecular nomenclature of increased precision and utility for genetic counseling, outcome prognostication, and treatment stratification.