Role of an Atypical Cadherin Gene, Cdh23 in Prepulse Inhibition, and Implication of CDH23 in Schizophrenia

Whole-genome sequencing to identify rare variants in East Asian patients with dementia with Lewy bodies

Dementia with Lewy bodies (DLB) is the second most common form of age-related dementia, following Alzheimer's disease (AD). DLB is associated with a worse prognosis than AD and is characterized by a more rapid progression of cognitive impairment and a poorer quality of life. In addition, the pathogenesis of DLB is less understood than that of AD, and only three genes-SNCA (α-synuclein), APOE (apolipoprotein E), and GBA1 (glucosylceramidase beta 1)-have been convincingly demonstrated to be associated with DLB. In this study, we utilized whole-genome sequencing data from 1744 Japanese individuals, comprising 45 DLB patients and 1699 cognitively normal older adults, aiming to identify new genes associated with DLB. Our genome-wide association studies of genes with potentially deleterious mutations identified the CDH23 gene as being associated with DLB, reaching a Bonferroni-corrected significance (P = 7.43 × 10-4). The gene contained three ethnicity-specific heterozygous missense variants (rs181275139, rs563688802, and rs137937502). CDH23 has been linked to deafness syndromes, and DLB patients carrying these mutations displayed symptoms of subjective hearing loss, suggesting a potential association between DLB onset and auditory impairment. Additionally, we explored human leukocyte antigen (HLA) genotypes associated with DLB but found no significant associations. This result suggests that the pathology of DLB differs from that of Parkinson's disease, which has been reported to have an association with HLA. Although a limitation of this study is the lack of replication of our findings, which require further validation in independent cohorts, our study enhances the understanding of the etiology of DLB in the Japanese population and provides new insights into the underlying mechanisms of its pathogenesis.

Rare Pathogenic Variants Identified in Whole Exome Sequencing of Monozygotic Twins With Autism Spectrum Disorder

BACKGROUND

Autism spectrum disorder (ASD) is a childhood-onset complex neurodevelopmental disorder characterized by problems with communication and social interaction and restricted, repetitive, stereotyped behavior. The prevalence of ASD is one in 36 children. The genetic architecture of ASD is complex in spite of its high heritability. To identify the potential candidate genes of ASD, we carried out a comprehensive genetic study of monozygotic (MZ) twins concordant or discordant for ASD.

METHODS

Five MZ twins and their parents were recruited for the study. Four of the twins were concordant, whereas one was discordant for ASD. Whole exome sequencing was conducted for the twins and their parents. The exome DNA was enriched using Twist Human Customized Core Exome Kit, and paired-end sequencing was performed on HiSeq system.

RESULTS

We identified several rare and pathogenic variants (homozygous recessive, compound heterozygous, de novo) in ASD-affected individuals.

CONCLUSION

We report novel variants in individuals diagnosed with ASD. Several of these genes are involved in brain-related functions and not previously reported in ASD. Intriguingly, some of the variants were observed in the genes involved in sensory perception (auditory [MYO15A, PLEC, CDH23, UBR3, GPSM2], olfactory [OR9K2], gustatory [TAS2R31], and visual [CDH23, UBR3]). This is the first comprehensive genetic study of MZ twins in an Indian population. Further validation is required to determine whether these variants are associated with ASD.

CDH23-Associated Usher Syndrome: Clinical Features, Retinal Imaging, and Natural History

Purpose

The purpose of this study was to analyze the clinical spectrum and natural history of CDH23-associated Usher syndrome type ID (USH1D).

Methods

Molecularly-confirmed individuals had data extracted from medical records. Retinal imaging was extracted from an in-house database. The main outcome measurements were retinal imaging and electroretinography (ERG) and clinical findings, including age of onset, symptoms, best-corrected visual acuity (BCVA), outer nuclear layer (ONL) thickness, ellipsoid zone width (EZW), and hyperautofluorescent ring area.

Results

Thirty-one patients were identified, harboring 40 variants in CDH23 (10 being novel). The mean (range, ±SD) age of symptom onset was 10.1 years (range = 1-18, SD = ±4.1). The most common visual symptoms at presentation were nyctalopia (93.5%) and peripheral vision difficulties (61.3%). The mean BCVA at baseline was 0.25 ± 0.22 in the right eyes and 0.35 ± 0.58 LogMAR in the left eyes. The mean annual loss rate in BCVA was 0.018 LogMAR/year over a mean follow-up of 9.5 years. Individuals harboring the c.5237G>A p.(Arg1746Gln) allele had retinitis pigmentosa (RP) sparing the superior retina. Seventy-seven percent of patients had hyperautofluorescent rings in fundus autofluorescence. Full-field and pattern ERGs indicated moderate-severe rod-cone or photoreceptor dysfunction with relative sparing of macular function in most patients tested. Optical coherence tomography (OCT) revealed intraretinal cysts in the transfoveal B-scan of 13 individuals (43.3%). The rate of EZW and ONL thickness loss was mild and suggestive of a wide window of macular preservation.

Conclusions

Despite the early onset of symptoms, USH1D has a slowly progressive phenotype. There is high interocular symmetry across all parameters, making it an attractive target for novel therapies.

Mice with deficiency in Pcdh15, a gene associated with bipolar disorders, exhibit significantly elevated diurnal amplitudes of locomotion and body temperature

Genetic factors significantly affect the pathogenesis of psychiatric disorders. However, the specific pathogenic mechanisms underlying these effects are not fully understood. Recent extensive genomic studies have implicated the protocadherin-related 15 (PCDH15) gene in the onset of psychiatric disorders, such as bipolar disorder (BD). To further investigate the pathogenesis of these psychiatric disorders, we developed a mouse model lacking Pcdh15. Notably, although PCDH15 is primarily identified as the causative gene of Usher syndrome, which presents with visual and auditory impairments, our mice with Pcdh15 homozygous deletion (Pcdh15-null) did not exhibit observable structural abnormalities in either the retina or the inner ear. The Pcdh15-null mice showed very high levels of spontaneous motor activity which was too disturbed to perform standard behavioral testing. However, the Pcdh15 heterozygous deletion mice (Pcdh15-het) exhibited enhanced spontaneous locomotor activity, reduced prepulse inhibition, and diminished cliff avoidance behavior. These observations agreed with the symptoms observed in patients with various psychiatric disorders and several mouse models of psychiatric diseases. Specifically, the hyperactivity may mirror the manic episodes in BD. To obtain a more physiological, long-term quantification of the hyperactive phenotype, we implanted nano tag® sensor chips in the animals, to enable the continuous monitoring of both activity and body temperature. During the light-off period, Pcdh15-null exhibited elevated activity and body temperature compared with wild-type (WT) mice. However, we observed a decreased body temperature during the light-on period. Comprehensive brain activity was visualized using c-Fos mapping, which was assessed during the activity and temperature peak and trough. There was a stark contrast between the distribution of c-Fos expression in Pcdh15-null and WT brains during both the light-on and light-off periods. These results provide valuable insights into the neural basis of the behavioral and thermal characteristics of Pcdh15-deletion mice. Therefore, Pcdh15-deletion mice can be a novel model for BD with mania and other psychiatric disorders, with a strong genetic component that satisfies both construct and surface validity.

Novel missense variants in brain morphogenic genes associated with depression and schizophrenia

Introduction

Impaired function of brain morphogenic genes is considered one of the predisposing factors for the manifestation of psychiatric and cognitive disorders, such as paranoid schizophrenia (SCZ) and major depressive disorder (MDD). Identification of such genes (genes of neurotrophic factors and guidance molecules among them) and their deleterious genetic variants serves as a key to diagnosis, prevention, and possibly treatment of such disorders. In this study, we have examined the prevalence of genomic variants in brain morphogenic genes in individuals with SCZ and MDD within a Russian population.

Methods

We have performed whole-exome sequencing of 21 DNA samples: 11 from individuals with SCZ and 10 with MDD, followed by ARMS (Amplification-Refractory Mutation System) based screening of detected single nucleotide variants (SNVs) in larger groups: 102 for individuals with SCZ, 79 for those with MDD and 103 for healthy donors.

Results

Whole-exome sequencing has revealed 226 missense mutations in 79 genes (out of 140 studied), some of which occur in patients with psychiatric disorders significantly more frequently than in healthy donors. We have identified previously undescribed genomic variants in brain morphogenic genes: CDH2 (rs1944294-T and rs17445840-T), DCHS2 (rs11935573-G and rs12500437-G/T) and CDH23 (rs1227051-G/A), significantly associated with the incidence of SCZ and MDD in the Russian population. For some SNVs (rs6265-T, rs1944294-T, rs11935573-G, rs4760-G) sex-biased differences in their prevalence between SCZ/MDD patients and healthy donors was detected.

Discussion

However, the functional significance of the SNVs identified has still to be confirmed in cellular and animal models. Once it is fulfilled, these SNVs have the potential to complement the diagnostic toolbox for assessing susceptibility to mental disorders. The data obtained indirectly confirm the importance of adequate brain structure formation for its correct functioning and preservation of mental health.

Which Came First? When Usher Syndrome Type 1 Couples with Neuropsychiatric Disorders

Usher syndrome (USH) is an autosomal recessive disorder characterized by sensorineural hearing loss (HL), retinopathy, and vestibular areflexia, with variable severity. Although a high prevalence of behavioural and mental disorders in USH patients has been reported, few studies on these psychiatric and psychological issues have been conducted. This work describes the case of a 16-year-old boy affected by congenital bilateral sensorineural HL, presenting a suddenly altered behaviour concomitant with a decrease in visual acuity. To establish a molecular diagnosis, Whole-Exome Sequencing analysis was performed, detecting a pathogenetic homozygous variant (c. 5985C>A, p.(Tyr1995*)) within the CDH23 gene. CDH23 is a known USH type 1 causative gene, recently associated with schizophrenia-like symptoms and bipolar disorders. To date, no studies have provided evidence of a direct genotype-phenotype correlation between USH patients carrying CDH23 variants and mental/behavioural issues; however, considering the multiple biological functions of CDH23, it can be hypothesised that it could have a pleiotropic effect. Overall, this study highlights the relevance of a continuous clinical evaluation of USH patients, to monitor not only the disease progression, but to early detect any psychological or behavioural alterations, thus allowing a rapid implementation of therapeutic strategies aimed at improving their quality of life and well-being.

Synaptic dysfunction in schizophrenia

Schizophrenia is a chronic disease presented with psychotic symptoms, negative symptoms, impairment in the reward system, and widespread neurocognitive deterioration. Disruption of synaptic connections in neural circuits is responsible for the disease's development and progression. Because deterioration in synaptic connections results in the impaired effective processing of information. Although structural impairments of the synapse, such as a decrease in dendritic spine density, have been shown in previous studies, functional impairments have also been revealed with the development of genetic and molecular analysis methods. In addition to abnormalities in protein complexes regulating exocytosis in the presynaptic region and impaired vesicle release, especially, changes in proteins related to postsynaptic signaling have been reported. In particular, impairments in postsynaptic density elements, glutamate receptors, and ion channels have been shown. At the same time, effects on cellular adhesion molecular structures such as neurexin, neuroligin, and cadherin family proteins were detected. Of course, the confusing effect of antipsychotic use in schizophrenia research should also be considered. Although antipsychotics have positive and negative effects on synapses, studies indicate synaptic deterioration in schizophrenia independent of drug use. In this review, the deterioration in synapse structure and function and the effects of antipsychotics on the synapse in schizophrenia will be discussed.

Tau-binding protein PRMT8 facilitates vacuole degeneration in the brain

Amyloid-β (Aβ) and tau pathologies are important factors leading to neurodegeneration in Alzheimer's disease (AD); however the molecular mechanisms that link these pathologies remain unclear. Assuming that important though as yet unidentified factors inhibit/accelerate tau pathology and neuronal cell death under amyloid pathology, we sought to isolate and identify tau-interacting proteins from mouse brains with or without amyloid pathology. Among the proteins that were identified, we focused on protein arginine methyltransferase 8 (PRMT8), which interacts with tau specifically in the absence of amyloid pathology. To investigate the role of PRMT8 in the pathogenesis of AD, we conducted Prmt8 gene deletion and overexpression experiments in AppNL-G-F/MAPT double-knock-in (dKI) mice and analyzed the resulting pathological alterations. PRMT8-knockout did not alter the AD pathology in dKI mice, whereas PRMT8-overexpression promoted tau phosphorylation, neuroinflammation, and vacuole degeneration. To evaluate if such a PRMT8-induced vacuole degeneration depends on tau pathology, PRMT8 was overexpressed in tau-KO mice, which were consequently found to exhibit vacuole degeneration. In addition, proteomic analyses showed that PRMT8 overexpression facilitated the arginine methylation of vimentin. Abnormal protein methylation could be involved in PRMT8-induced brain pathologies. Taken together, PRMT8 may play an important role in the formation of tau pathology and vacuole degeneration.

A loss-of-function variant in SUV39H2 identified in autism-spectrum disorder causes altered H3K9 trimethylation and dysregulation of protocadherin β-cluster genes in the developing brain

Recent evidence has documented the potential roles of histone-modifying enzymes in autism-spectrum disorder (ASD). Aberrant histone H3 lysine 9 (H3K9) dimethylation resulting from genetic variants in histone methyltransferases is known for neurodevelopmental and behavioral anomalies. However, a systematic examination of H3K9 methylation dynamics in ASD is lacking. Here we resequenced nine genes for histone methyltransferases and demethylases involved in H3K9 methylation in individuals with ASD and healthy controls using targeted next-generation sequencing. We identified a novel rare variant (A211S) in the SUV39H2, which was predicted to be deleterious. The variant showed strongly reduced histone methyltransferase activity in vitro. In silico analysis showed that the variant destabilizes the hydrophobic core and allosterically affects the enzyme activity. The Suv39h2-KO mice displayed hyperactivity and reduced behavioral flexibility in learning the tasks that required complex behavioral adaptation, which is relevant for ASD. The Suv39h2 deficit evoked an elevated expression of a subset of protocadherin β (Pcdhb) cluster genes in the embryonic brain, which is attributable to the loss of H3K9 trimethylation (me3) at the gene promoters. Reduced H3K9me3 persisted in the cerebellum of Suv39h2-deficient mice to an adult stage. Congruently, reduced expression of SUV39H1 and SUV39H2 in the postmortem brain samples of ASD individuals was observed, underscoring the role of H3K9me3 deficiency in ASD etiology. The present study provides direct evidence for the role of SUV39H2 in ASD and suggests a molecular cascade of SUV39H2 dysfunction leading to H3K9me3 deficiency followed by an untimely, elevated expression of Pcdhb cluster genes during early neurodevelopment.