Congenital hydrocephalus: a review of recent advances in genetic etiology and molecular mechanisms

The global prevalence rate for congenital hydrocephalus (CH) is approximately one out of every five hundred births with multifaceted predisposing factors at play. Genetic influences stand as a major contributor to CH pathogenesis, and epidemiological evidence suggests their involvement in up to 40% of all cases observed globally. Knowledge about an individual’s genetic susceptibility can significantly improve prognostic precision while aiding clinical decision-making processes. However, the precise genetic etiology has only been pinpointed in fewer than 5% of human instances. More occurrences of CH cases are required for comprehensive gene sequencing aimed at uncovering additional potential genetic loci. A deeper comprehension of its underlying genetics may offer invaluable insights into the molecular and cellular basis of this brain disorder. This review provides a summary of pertinent genes identified through gene sequencing technologies in humans, in addition to the 4 genes currently associated with CH (two X-linked genes L1CAM and AP1S2, two autosomal recessive MPDZ and CCDC88C). Others predominantly participate in aqueduct abnormalities, ciliary movement, and nervous system development. The prospective CH-related genes revealed through animal model gene-editing techniques are further outlined, focusing mainly on 4 pathways, namely cilia synthesis and movement, ion channels and transportation, Reissner’s fiber (RF) synthesis, cell apoptosis, and neurogenesis. Notably, the proper functioning of motile cilia provides significant impulsion for cerebrospinal fluid (CSF) circulation within the brain ventricles while mutations in cilia-related genes constitute a primary cause underlying this condition. So far, only a limited number of CH-associated genes have been identified in humans. The integration of genotype and phenotype for disease diagnosis represents a new trend in the medical field. Animal models provide insights into the pathogenesis of CH and contribute to our understanding of its association with related complications, such as renal cysts, scoliosis, and cardiomyopathy, as these genes may also play a role in the development of these diseases. Genes discovered in animals present potential targets for new treatments but require further validation through future human studies.


Background
Congenital hydrocephalus (CH) is characterized by the excessive accumulation of cerebrospinal fluid (CSF) in the brain at birth [1].The incidence of CH is approximately 1/500 among young individuals and 2/500 among the elderly.It is a complex brain disorder with multiple etiological factors, including vitamin B or folic acid deficiency, intraventricular hemorrhage, viral infections, environmental influences, developmental anomalies, and genetic predisposition, often accompanied by structural brain abnormalities and neural dysfunction [2].Common symptoms of hydrocephalus include gait disturbances, cognitive impairment, urinary dysfunction, seizures, abnormal reflexes, bradycardia and hypoventilation, headaches, vomiting, and visual impairments [3].Among these factors contributing to CH development, global epidemiological data suggests that genetic factors account for more than 40% of cases [4,5].The annual medical costs associated with hydrocephalus are estimated at around $2 billion per year in the US alone, thus posing a significant economic and societal burden [6].
Though genetic factors contribute to up to 40% of cases of CH, precise genetic causes have only been identified in less than 5% of human cases [4].There is a pressing need for a deeper understanding of the genetic components and mechanisms underlying CH, which has the potential to yield invaluable insights into its molecular and cellular etiology [7].This review aims to consolidate existing evidence on the pathologic genes implicated in both human patients and animal models with respect to CH development.The goal is to stimulate novel approaches towards treating CH.Additionally, we discuss other developmental disorders and organ dysfunctions associated with genes related to hydrocephalus.

The production and circulation of CSF
CSF plays a critical role not only in providing mechanical support for the brain and spinal cord but also serves as a carrier for transporting metabolic waste and nutrients [8].The healthy brain consists of three integrated components that collectively regulate CSF dynamics: CSF production, circulation, and absorption.These three components typically maintain equilibrium.
Approximately 80-90% of CSF is produced by the choroid plexus in the cerebral lateral ventricles [9,10] (Fig. 1).Ion transporters on the basolateral membrane Fig. 1 The production of CSF occurs through two distinct pathways: the choroid plexus and the brain parenchymal system.CSF can be absorbed by the subarachnoid space or glymphatic circulation, ultimately entering the dcLNs.CSF cerebrospinal fluid, dcLNs deep cervical lymphatic nodes, ISF interstitial fluid, mLVs meningeal lymphatic vessels facing the blood and the apical membrane facing the ventricles are responsible for secreting and delivering ions such as Na + , Cl − and HCO 3 − from the blood to the ventricles [11][12][13].The remaining 10-20% of CSF production is attributed to the brain parenchymal system through exchange between CSF and interstitial fluid (ISF) in the capillary-astrocyte complex.
Most researchers have hypothesized that the circulation of CSF commences from the lateral ventricles, proceeds into the third ventricle, and then passes into the fourth ventricle through the midbrain cerebral aqueduct.The majority of CSF subsequently flows into the cisterna magna and cerebellopontine cisterns via the apertures of the fourth ventricle, namely, the median aperture and two lateral apertures.Ultimately, it is reabsorbed into the cerebral venous system through the arachnoid villi [14].The extracranial lymphatic drainage pathway serves as a crucial component of CSF circulation, playing a pivotal role in maintaining homeostasis, buffering functions, and protective mechanisms of the central nervous system (CNS) [15].As illustrated in Fig. 1, a significant volume of CSF drains into nasal lymph nodes and meningeal lymphatic vessels (mLVs), through which CSF is removed from intracranial spaces to extracranial regions and subsequently absorbed by the deep cervical lymphatic nodes (dcLNs) [16].This intricate physiological process involves interactions among multiple molecules.Therefore, in subsequent sections, we will focus on pathological mechanisms related to molecular dysfunctions causing hydrocephalus.Disruption in any of these processes could lead to excessive accumulation of CSF and ventriculomegaly due to factors such as CSF overproduction, inefficient reabsorption into the systemic circulation, abnormal cilium-dependent flow, or obstruction within the ventricular system.

The main genetic target of CH in humans
Genes associated with CH in human cases are presented in Fig. 2, most of which are involved in Sylvius aqueduct (SA) defects, cilia growth and movement, and nervous system development.The Human Phenotype Ontology website predicts that 411 genes are related Fig. 2 The genetic targets of CH in humans involve genes related to cilia movement, Sylvius aqueduct development, and nervous system growth in pathological cases of CH.CH congenital hydrocephalus, FOXJ1 forkhead box J1, CWH43 cell wall biogenesis 43 C-terminal homolog, AK9 adenylate kinase 9, AP1S2 adaptor related protein complex 1 subunit sigma 2, CCDC88C coiled-coil domain containing 88C, L1CAM L1 cell adhesion molecule, TR1M71 tripartite motif containing 71, SMARCC1 SWI/SNF related, matrix associated, actin dependent regulator of chromatin subfamily C member 1, PTCH1 patched 1, SHH sonic hedgehog, MPDZ multiple PDZ domain crumbs cell polarity complex component, CRB2 crumbs cell polarity complex component 2 to "hydrocephalus" (HP:0000238).Among them, only 4 genes have been confirmed to be linked to CH: two X-linked genes [L1CAM (L1 cell adhesion molecule) and AP1S2 (adaptor-related protein complex 1 subunit sigma 2)] and two autosomal recessive genes [MPDZ (multiple PDZ domain crumbs cell polarity complex component) and CCDC88C (coiled-coil domain containing 88C)].
SA stenosis, which connects the third and fourth ventricles, is responsible for the majority of cases of non-syndromic CH.Approximately 5-15% of cases are associated with X-linked variations of L1CAM, known as L1 syndrome.L1CAM encodes a transmembrane glycoprotein belonging to the immunoglobulin superfamily of cell adhesion molecules, and it plays important roles in neuronal adhesion, migration, growth cone morphology, neurite outgrowth, and myelination.Another separate X-linked syndrome called Fried-Pettigrew syndrome [Online Mendelian Inheritance in Man (OMIM): 304,340], is characterized primarily by intellectual disability, basal ganglia iron or calcium deposition, and hydrocephalus due to AP1S2 variation [17][18][19].Variations in MPDZ and CCDC88C share many neuropathological similarities including atresia of both SA and the central canal of the medulla with recessive forms of CH (OMIM: 615,219 and OMIM: 236,600 respectively).Both genes colocalize at the apical cell junction in the neural plate, CCDC88C directly interacts with MPDZ and cooperates to promote apical cell constriction during neurulation [20,21].MPDZ is essential for maintaining ependymal integrity, loss of MPDZ leads to ependymal denudation accompanied by reactive astrogliosis and SA stenosis [22].Additionally, mutations in MPDZ can cause abnormally high permeability in choroid plexus epithelial cell monolayers [23].
Moreover, this section also provides a summary of the mutation genes identified through gene sequencing technology in cases of hydrocephalus and related diseases, which require further validation to establish their causal involvement in hydrocephalus.Regarding SA development-related genes, CRB2 encodes the crumbs cell polarity complex component 2, originally primarily associated with renal anomalies such as renal tubular or glomerular microcysts.Recently, Tessier et al. [24] reported that biallelic CRB2 variations are also strongly linked to hydrocephalus, resulting from atresia of the SA and central canal aqueduct of the medulla.
For the genes related to cilia growth and motility, CWH43 (cell wall biogenesis 43 C-terminal homolog) is highly expressed in ciliated ependymal and choroid plexus cells, where it regulates the membrane localization of glucose-6-phosphate isomerase (GPI)-anchored proteins in mammalian cells.Yang et al. [25] found that approximately 15% of patients with idiopathic normal pressure hydrocephalus (iNPH) carry heterozygous loss-of-function deletions in CWH43.Similarly, mice with Cwh43 deletions could develop communicating hydrocephalus, gait dysfunction, and abnormalities in choroid plexus and ependymal cells.The mutation of CWH43 affects the number of ependymal cilia and the apical/basal targeting of GPI-anchored proteins in ventricular multi-ciliated epithelial cells, which may contribute to the development of iNPH.AK9, encoding adenylate kinase 9, was also suggested to be involved in iNPH.A damaging mutation in AK9 was detected in 9.6% of iNPH patients [26].Mice with Ak9 mutation exhibit decreased cilia motility and beat frequency, as a result of communicating hydrocephalus and balance impairment.Dysfunction of the FOXJ1 (forkhead box J1) triggers autosomal dominant motile ciliopathies affecting many organ systems, including brain ventricles leading mainly to abnormal ventricular ciliary motility in CH [27].CC2D2A (coiled-coil and C2 domain containing 2A) mutations are a relatively common cause of Joubert syndrome, a ciliopathy characterized by distinctive brain malformation and developmental delay.Patients with CC2D2A mutations often present with hydrocephalus or epilepsy [28].Furthermore, Munch et al. [29] investigation revealed that 14 genes are involved in ciliogenesis, CELSR2 (cadherin EGF LAG seven-pass G-type receptor 2), CENPF (centromere protein F), DNAI1 (dynein axonemal intermediate chain 1), DNAH5 (dynein axonemal heavy chain 5), FLNA (filamin A), FUZ (fuzzy planar cell polarity protein), IFT172 (intraflagellar transport 172), LRP6 (LDL receptor-related protein 6), MPDZ, NOTCH2 (Notch receptor 2), PIK3R2 (phosphoinositide-3-kinase regulatory subunit 2), PTCH1 (patched 1), TRIM71 (tripartite motif containing 71), and VANGL2 (VANGL planar cell polarity protein 2).
In addition, several genes have been identified as being related to hydrocephalus, but the reporting of this relationship has been incomplete.MMACHC (metabolism of cobalamin associated C) mutation with c.609G > A is most frequently observed in patients with cobalamin C deficiency (cblC).Recent research has shown that the homologous mutation MMACHC c.609G > A often leads to irreversible brain disorders such as developmental delay, seizures, and hydrocephalus [34].Furthermore, a study of 27 CH families revealed that the WDR81 (WD repeat domain 81) and EML1 (EMAP like 1) genes are associated with CH [35].Another study involving 381 sporadic CH cases (232 trios) identified several new risk genes of CH including PIK3CA (phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha), PTEN (phosphatase and tensin homolog), mTOR (mechanistic target of rapamycin kinase), FMN2 (formin 2), and FXYD2 (FXYD domain-containing ion transport regulator 2) [19].Additionally, a study of 110 infantile hydrocephalus cases indicated that ZEB1 (zinc finger E-box binding homeobox 1), SBF2 (SET binding factor 2), and GNAI2 (G protein subunit alpha i2) were over-represented and might affect the signaling pathways involved in infantile hydrocephalus formation [36].
Overall, due to limited data and research, the current findings can only account for less than 5% of primary CH cases [37].Further genome sequencing of large, well-phenotype cohorts is necessary to gain a deeper understanding of the molecular and cellular etiology of CH.

The main genetic targets of CH in animal models
Animal models of CH exhibit numerous histopathological similarities to humans, making them valuable for studying the genetics and pathogenesis of CH.Many genetic loci associated with hydrocephalus have been identified in animal models [38].In this section, we provide a summary of CH-related genes discovered in animal models, most of which are related to cilia synthesis and movement, ion transportation, RF synthesis, cell apoptosis, and neurogenesis (Fig. 3).

Cilia-related genes
Ciliated structures composed of microtubules form elongated protrusions on cellular membranes, they can be found in various cell types including ependymal cells.Cilia can be classified into two categories: primary cilium which serves primarily as a sensor for signal transduction [39], and motile cilium is found predominantly on specialized cells responsible for fluid movement or cell propulsion through outer dynein arms (ODA) and inner dynein arms (IDA) [40].Malfunctioning ciliary activity may lead to genetic developmental disorders associated with primary ciliary dyskinesia (PCD), leading to conditions such as infertility, developmental anomalies, hydrocephalus, and auditory issues along with compromised respiratory pathogens clearance leading susceptibility towards infections causing persistent coughing and dyspnea [41].Ependymal cells are located in the superficial layer of the cerebral ventricle walls and the central canal of the spinal cord.The cilia on these cells play a role in producing and circulating CSF as well as contributing to nerve regeneration.Both primary and motile cilia are involved in hydrocephalus through distinct mechanisms related to their physiological functions.Cilia distributed in various regions of the ventricles work together to maintain the directional flow of CSF.Growing evidence indicated that coordinated beating of motile cilia generates significant force, propelling CSF production and circulation within brain ventricles [42,43].Impairment of ciliary motor function can disrupt the balance between CSF production and circulation, resulting in the accumulation of CSF in the ventricles.Table 1 presents a list of 28 genes that regulate the structure and function of cilia .
Wdr16 (cilia and flagella-associated protein 52) plays a crucial role in cilia-related signal transduction.In zebrafish, severe hydrocephalus was observed in the Wdr16 gene knockdown zebrafish.It is noteworthy that hydrocephalus was the phenotype of Wdr16 disruption in zebrafish, but ependymal disorganization or impaired ciliary motility was not observed [44,45].It's speculated that Wdr16 regulates hydrocephalus through ciliamediated cell polarity effects such as water homeostasis or osmoregulation.Wdr78 (dynein axonemal intermediate chain 4) encodes a motile cilium-specific protein involved in the assembly of the axon dynein complex and ciliary movement.Depletion of Wdr78 in mice caused defects in ependymal cilia, while Wdr78 morphants zebrafish exhibited ciliopathy-associated phenotypes such as hydrocephalus, pronephric cysts, or abnormal otoliths [46].Therefore, studies have shown that depletion of Wdr78 leads to abnormal ciliary beat function of ectodermal cells by affecting the dynein-f assembly.Nphp7 (nephrocystin 7) is a type of transcription factor and has been found to physically interact with Bardet-Biedl syndrome 1 (BBS1).A previous study indicated that hydrocephalus and pronephric cysts were displayed in the Nphp7 zebrafish morphants [47].It is noteworthy that the deletion of Nphp7 revealed an astonishingly impaired ciliary motility.

Ion channels and ion transporter-related genes
Ion transporters play important roles in the process of CSF secretion.Due to the unidirectional nature of ion movement, transporters located on the basement membrane side differ from those on the apical membrane side.These transporters effectively maintain internal homeostasis and balance of Na + , Cl − , and HCO 3 − , which in turn regulate CSF secretion.In this section, we examine 6 genes associated with ion transporter function, whose dysfunction could impact CSF secretion and lead to hydrocephalus (Table 1) [75][76][77][78][79].
Calb2 (calbindin 2) belongs to the troponin C superfamily of Ca 2+ binding protein and is involved in Ca 2+ transportation.In zebrafish, Calb2a and Calb2b are highly expressed in the CNS and peripheral nervous system, where they play a crucial role in regulating synaptic calcium concentration, thus contributing significantly to nervous system development.The combined loss of Calb2a and Calb2b leads to severe hydrocephalus, axial curvature defect, and yolk sac edema in zebrafish due to impaired neural tube folding and disorganized midbrain-hindbrain boundary [76].Atp1a3 (ATPase Na + /K + transporting subunit α3) encodes an essential ion-transporting enzyme that regulates transmembrane Na + and K + gradients, playing a vital role in electrical excitation transmission of nerve and muscles.The Atp1a3 knockdown in zebrafish can result in hydrocephalus due to disrupted transmembrane ion transport [78].Slc41a1 (solute carrier family 41 member 1) encodes Mg 2+ transporter proteins located at the base membrane that participate in the transmembrane transport of Mg 2+ .Knockdown of Slc41a1 with morpholino leads to body curvature, hydrocephalus, and kidney cysts in zebrafish as a result of disrupted intracellular Mg 2+ homeostasis caused by blocked transmembrane Mg 2+ transport [79].

CNS-related genes
CH is not only a disorder of CSF dynamics, but also a brain disorder that leads to severe neurological impairment [80].Most cells in the developing mammalian brain derive from the ventricular (VZ) and subventricular (SVZ) zones.The VZ consists of multipotent radial glia/NSCs, while the SVZ is composed of rapidly proliferating neural precursor cells (NPCs) [81].These zones are crucial for neurodevelopment and any disruption, particularly within the VZ, can lead to stenosis or obliteration of the cerebral aqueduct of Sylvius, ultimately resulting in hydrocephalus [82][83][84].This disturbance not only affects CSF flow but also simultaneously impairs the function of NSCs and ependymal cells, thereby linking hydrocephalus with abnormal neurogenesis [85][86][87].Moreover, defects in membrane protein transporterrelated genes could disrupt NSCs, leading to CH and associated cerebral malformations [1,[88][89][90].Rodríguez et al. [82] proposed that gene mutations associated with cell junction proteins' transport in NSCs could lead to the disruption of VZ, thereby resulting in aqueduct stenosis and hydrocephalus.NSCs play an important role in the growth of neurons and glial cells in the CNS [91,92].The dysfunction of NSC function hinders the polarity, proliferation, and differentiation of neurons.It is worth noting that NSC injury can also induce neurological disorders, such as cortical dysfunction, hydrocephalus, and periventricular heterotopia [91,93].Additionally, it is noteworthy that apoptosis within the CNS may impact neuronal development, resulting in hydrocephalus and nasal malformations [94].In this section, we review 7 genes associated with CNS, whose dysfunction could contribute to hydrocephalus (Table 1) [82,[95][96][97][98][99][100].
Pank2 (pantothenate kinase 2) encodes a protein belonging to the pantothenate kinase family and plays an essential role in cellular coenzyme A biosynthesis.Pank2 morphant in zebrafish induced abnormal phenotypes including disrupted brain morphology, hydrocephalus, and edema in the heart region [95].Downregulation of Pank2 significantly impacts the development of neurons in the CNS and neuronal cells.Ecrg4 (esophageal cancer-related gene 4) regulates the secretion of neuropeptides and is mainly expressed in the choroid plexus (CP) epithelial cells, brain ventricular, and central canal cells of the spinal cord.The product of Ecrg4, Augurin, contributes to the development of CNS and participates in the proliferation of NSC and NPC.Knockdown of Ecrg4 using morpholino in zebrafish induced a hydrocephaluslike phenotype related to the damage of CNS [96].

Subcommissural organ (SCO)-RF-related genes
RF, a network of threadlike glycoproteins suspended within the CSF, plays a pivotal role in the homeostatic regulation of the brain's internal environment, by binding to and facilitating the transport and clearance of monoaminergic compounds.It is produced and released from the SCO of the brain, an active gland during development in most species including humans [101].The SCO is an ependymal structure located at the roof of the third ventricle and the entrance to the mesencephalic aqueduct [102][103][104].The RF extends through the SA, fourth ventricle, and central canal of the spinal cord to reach the caudal ampulla or fifth ventricle located at the end of the central canal [101].Dysfunction of the SCO-RF complex is closely related to hydrocephalus phenotypes [103,105].Evidence suggested that the absence of RF or immunological damage to SCO could lead to stenosis or obliteration of cerebral aqueduct and defects in the neural canal (NCa), thereby impairing CSF circulation resulting in CH [106][107][108].Moreover, the role of RF extends to neural development and axonal guidance, with its deficiency being associated with morphological brain defects, highlighting its multifaceted contribution to both normal physiology and disease pathology [88].It is worth noting that RF is exclusively present in animals, except for humans.In humans, the secretory capacity of the SCO is robust in 3-5-month-old fetuses; however, it regresses significantly in 9-month fetuses.By 1-year-old, secretory ependymal cells shrink and cluster into islets interspersed with non-secretory cuboidal ependyma.This regression continues through childhood, limiting secretory parenchyma to scattered islets by the ninth year.Despite the absence of RF in humans, SCO-spondin, the unpolymerized form of RF, is present and soluble in CSF, thus impacting brain development [109].It also participates in certain aspects of neurogenesis, such as the cell cycle of NSCs, neuronal differentiation, and axon pathfinding [104].In this section, we discuss 2 genes linked to RF function that contribute to the development of hydrocephalus (Table 1) [105,110].
Camal encodes a protein associated with cell adhesion.Camel regulates the development of brain ventricular, and loss of camel function in zebrafish leads to the manifestation of hydrocephalus and scoliosis.Deletion of camel has been shown to result in hydrocephalus due to defects in RF synthesis, resulting from abnormal CSF flow [105].Msx1 (Msh homeobox 1) is involved in regulating DNA-binding transcription factor activity and is widely expressed in neuroepithelial cells.Msx1 mutants exhibit severe hydrocephalus at birth, accompanied by abnormal SCO development.Additionally, RF was found to be absent in Msx1 mutant mice [110].This suggests that Msx1 mutants inhibit RF synthesis by affecting normal SCO development, thereby affecting CSF flow.

Others
Table 1 also highlights five additional genes and small molecular substances linked to hydrocephalus [111][112][113][114][115].However, the mechanisms by which these genes  influence the progression of hydrocephalus are not fully understood or categorized as mentioned earlier.Furthermore, the inflammatory/immune response may also be associated with the progression and severity of hydrocephalus [2,116].In the hyh mice and HTx rats (two animal models of fetal-onset hydrocephalus), the onset of ventricle disruption is correlated with the infiltration of macrophages and lymphocytes into denuded.The expression of β-Pix [Rho guanine nucleotide exchange factor (GEF) 7b] is widespread in both the brain and blood vessels, where it plays a role in regulating cerebral vascular stability.In zebrafish, mutation of the β-Pix gene can lead to obvious hydrocephalus and severe intracranial hemorrhage during early embryonic development.It has been hypothesized that deleting β-Pix may disrupt vascular stability, potentially affecting CSF circulation [112].Thioredoxin1 is an antioxidant protein with reactive oxygen species (ROS) scavenging capabilities that govern processes such as cell proliferation, migration, apoptosis, and inflammation.Zebrafish injected with thioredoxin1 morpholine exhibit hydrocephalus and midbrain malformations [115].Deletion of thioredoxin1 triggers a significant increase in ventricular epithelial cell apoptosis while disrupting vascular endothelial cell migration, ultimately leading to hydrocephalus.

Discussion
In this review, we have comprehensively summarized the genetic factors and molecular mechanisms of CH in both human subjects and animal models.The results from human sequencing and validated genes showed that these genes are related to dysfunction of the central system, impaired cilia movement, and abnormalities in SA.By utilizing animal models such as mice and zebrafish, it becomes feasible to further investigate additional genes related to hydrocephalus pathology.These genes can be systematically classified into 4 principal groups: those linked to ciliary function, ion transport, CNS function, and RF synthesis.Genes related to ciliary function play an important role in regulating the synthesis, formation, and movement of cilia, which is closely connected with CSF absorption.Ion transporter-related genes primarily disrupt homeostasis by dysregulating the ions' transportation processes, thus impacting CSF secretion.Mutation in CNS function-related genes predominantly affects the development, function, and apoptosis of nerve cells, which might result in potential disturbances in brain morphology.Additionally, the RF synthesis-related genes dysregulate the formation and morphology of NCa, influencing CSF circulation.The identification of these genes in CH animal models provides valuable resources for validation within larger clinical cohorts of CH patients.Genetic insights hold profound significance in the management of CH.The pathogenesis of this complex disease may be closely linked to multiple gene variants.Genetic research aids in identifying these key gene variants, thereby unraveling the underlying mechanisms of the disease and paving the way for innovative treatment approaches [117].For instance, if a specific genetic variant is found to be intricately associated with the disease, gene-editing techniques or gene therapy can be employed to correct this variant, ultimately aiming to cure the condition [118][119][120].Furthermore, genetic understanding promotes personalized healthcare.As each individual has a unique genome, responses to illnesses and treatment outcomes naturally differ.Genetic research enables tailored therapies based on a patient's genotype, optimizing treatment efficiency and minimizing adverse effects [121].Moreover, genetic insights facilitate more accurate disease prediction and risk assessment.Genetic screenings allow us to anticipate an individual's susceptibility to certain illnesses, enabling proactive preventive measures.This prediction is particularly crucial for genetic conditions such as CH.In conclusion, genetic insights offer immense potential to revolutionize disease treatment.As genetic research advances and technology evolves, we are poised to deliver more precise and effective medical care in the foreseeable future.Nevertheless, it is crucial to recognize that genetics do not hold all the answers, they address only a portion of health conditions.Hence, a holistic approach encompassing genetics as well as environment and lifestyle factors is essential for devising comprehensive treatment plans.
Addressing the complexities associated with CH necessitates developing a multimodal detection approach that integrates both clinical observations along radiological phenotypic characteristics alongside genotypic analysis for effective implementation within a clinical setting.This comprehensive approach plays a pivotal role in augmenting diagnostic precision and specificity, crucial when dealing with conditions where initial symptoms may not manifest at birth but evolve gradually over time.The utilization of clinical radiological medical imaging technology like CT as well as MRI offers substantial benefits, particularly in identifying structural anomalies within the brain including aqueduct stenosis, Dandy-Walker malformation, arachnoid cysts, and neural tube defects.Additionally, the insight provided by genotype data facilitates a deeper understanding of the onset and progression mechanisms related to CH pathology.However, it should be noted that genetic analysis alone may have limitations when elucidating complex presentations involving skull morphology, extracranial structures, and skeletal deformities.Therefore, a synergistic amalgamation encompassing genotype data along with detailed examination through clinical and radiologic means holds promise for expediting precise disease identification.Zhang et al. [122] integrated key findings from their study which involved combining patient-specific traits, and molecular analyses via neuroimaging modalities such as MRI/CT scans, gene mutation tests, and metabolic assessments.Moreover, Rijken et al. [123] demonstrated how 3D-CT reconstruction technology played an indispensable role in delineating morphometric changes in foramen magnum configuration as well as the presence of ventriculomegaly among pediatric patients diagnosed with craniosynostosis; this technique exhibits considerable potential for facilitating CH diagnostics.Consequently, this multimodal detection strategy, involving integration between radiologically derived phenotypes and genotype analytics, serves not only to enhance diagnostic precision and treatment efficacy but also paves the way for tailored medical interventions catering to individual patient needs.With ongoing advancements in technology-driven genomic research coupled with expanding horizons within clinical applications, it is anticipated that future management strategies will enable more accurate and effective treatment across diverse spectrums of ailments.
The phenotypic manifestations of genetic defects are remarkably diverse and complex.Pathogenic genes associated with hydrocephalus may also present in other tissues or organs, leading to a range of comorbidities.For instance, dysfunctional ciliary genes can also trigger renal cysts and scoliosis [46,48,49,54,56,58].Additionally, the loss of function of the SLC25A4 gene can lead to severe cardiomyopathy, scoliosis, cataracts, and depression [124].Understanding the associated complications of hydrocephalus is essential for identifying the underlying pathology and implementing personalized treatment.If patients exhibit symptoms of hydrocephalus, early intervention, and targeted treatments should be provided to prevent associated comorbidities.
Further research into the genetic and pathogenesis of CH will facilitate the development of animal models for investigating drug treatment options.Currently, the field of drug therapy for CH remains largely unexplored, and establishing effective animal models of hydrocephalus provides a platform for exploring potential drug targets.

Conclusions
In this review, we have provided a comprehensive summary of recent discoveries regarding the genetic targets of CH in both human and animal models.In addition to the 4 confirmed genes associated with CH (X-linked genes L1CAM and AP1S2, autosomal recessive MPDZ, and CCDC88C).We have also reviewed 35 genes identified through gene sequencing in human cases, as well as numerous related genes in the CH animal model.These findings warrant further validation through extensive clinical studies involving a large cohort of CH patients.The implicated genes primarily participate in 4 pathways and may contribute to comorbidities affecting other organ functions where these related genes are expressed.

Table 1
List of potential CH-related genes in animal models