Hydrocephalus in Connection to Genetic Mutation in Cranial Neural Crest Cells

Hydrocephalus, a pathological condition due to the accumulation of cerebrospinal fluid (CSF) in the brain's ventricles, has been recognised as a relatively common brain abnormality in newborns and young adults with or without craniofacial anomaly. It can cause physical, behavioural and cognitive symptoms and, in severe cases, may result in lethality. Hydrocephalus can result from various underlying conditions, and its multifactorial nature makes pinpointing a single pathophysiological aetiology challenging. Notably, the relatively high prevalence of hydrocephalus (up to 100%) in the cranial neural crest cells (CNCCs) conditional knockout mouse models of various genes using Wnt1-Cre has been reported, given the extremely low (0.01% to 0.86%) spontaneous occurrence of hydrocephalus in different strains of lab mice. Surprisingly, there were no reports on the connections of hydrocephalus with CNCCs, although the prominent role of CNCCs in normal development and pathologic conditions of craniofacial and neural tissues has been extensively studied and highly recognised. In this review, besides revealing the high prevalence of hydrocephalus (5.4%-100%), we primarily summarised the in vivo findings of hydrocephalus and the associated pathological changes of brain and craniofacial skeletal tissues with the genetically modified mouse (GMM) models of various genes knocked out in CNCCs. Significantly, the functional gene knockout in Wnt1 expressing cells can lead to hydrocephalus and associated brain and craniofacial skeletal pathologies, irrespective of the ectopic midbrain Wnt1 activation observed in Wnt1-Cre driver mice. However, the specific contributions and underpinning mechanisms of the main structures of the CSF system, including CNCCs-derived choroid plexus, to hydrocephalus pathophysiology are yet to be fully elucidated.