Rare genetic brain disorders with overlapping neurological and psychiatric phenotypes

Etiology of nephrotic syndrome: insights from univariate and multivariate Mendelian randomization study

Nephrotic syndrome (NS) is a common cause of chronic glomerular disease. However, the precise way in which one or more risk exposure traits of renal injury lead to NS remains unclear. In this study, we systematically examined the causal relationships between NS and various exposure traits, including traits related to chronic hepatitis B/C infection, COVID-19 (hospitalized), general allergy status, herbal tea intake, immunoglobulin E, childhood obesity, and the human leukocyte antigen (HLA)-II histocompatibility DM α/DP β1/DQ α2 chain, via multivariate Mendelian randomization (MVMR). A previously reported exposure trait, ulcerative colitis, was also included to analyze the independent effect of each significant exposure on the risk of developing NS. In the univariable MR analysis, immunoglobulin E (OR = 5.62, 95% CI = 2.91-10.84, p = 2.67 × 10-7) and the HLA-II histocompatibility DQ α2 chain (OR = 0.70, 95% CI = 0.63-0.80, p = 2.83 × 10-7) were shown to have effect estimates consistent with a greater risk of developing NS. The reverse MR analysis showed no evidence of causal effect from NS to histocompatibility DQ α2 chain (p = 0.76). In MVMR, only the HLA-II histocompatibility DQ α2 chain retained a robust effect (OR = 0.71, 95% CI = 0.61-0.82; p = 9.39 × 10-6), and the estimate for immunoglobulin E was weakened (OR = 1.04, 95% CI = 0.60-2.13; p = 0.92). With two independent ulcerative colitis resources used for validation, ulcerative colitis was not significantly associated with NS. This study provides genetic evidence that the HLA-II histocompatibility DQ α2 chain has a predominant causal effect on the risk of developing NS. HLA-II histocompatibility-mediated immune abnormalities may lead to subtypes of NS and its pathological changes.

Developmental variability in paediatric SGCE-related myoclonus dystonia syndrome

This commentary is on the original article by De Francesch et al. on pages  740–749  of this issue.

GluA2-containing AMPA receptors form a continuum of Ca2+-permeable channels

Fast excitatory neurotransmission in the mammalian brain is mediated by cation-selective AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptors (AMPARs)1. AMPARs are critical for the learning and memory mechanisms of Hebbian plasticity2 and glutamatergic synapse homeostasis3, with recent work establishing that AMPAR missense mutations can cause autism and intellectual disability4-7. AMPARs have been grouped into two functionally distinct tetrameric assemblies based on the inclusion or exclusion of the GluA2 subunit that determines Ca2+ permeability through RNA editing8,9. GluA2-containing AMPARs are the most abundant in the central nervous system and considered to be Ca2+ impermeable10. Here we show this is not the case. Contrary to conventional understanding, GluA2-containing AMPARs form a continuum of polyamine-insensitive ion channels with varying degrees of Ca2+ permeability. Their ability to transport Ca2+ is shaped by the subunit composition of AMPAR tetramers as well as the spatial orientation of transmembrane AMPAR regulatory proteins and cornichon auxiliary subunits. Ca2+ crosses the ion-conduction pathway by docking to an extracellular binding site that helps funnel divalent ions into the pore selectivity filter. The dynamic range in Ca2+ permeability, however, arises because auxiliary subunits primarily modify the selectivity filter. Taken together, our work proposes a broader role for AMPARs in Ca2+ signalling in the mammalian brain and offers mechanistic insight into the pathogenic nature of missense mutations.

Demographic, Premorbid, and Clinical Characteristics of Schizophrenia Spectrum Patients with High and Low Polygenic Liability to the Disorder

BACKGROUND/OBJECTIVES

Schizophrenia is a clinically heterogeneous complex disorder with a substantial polygenic basis. The discovery of phenotypes indexing genetic differences advances research into the schizophrenia etiology but has proven to be challenging. The study aimed to further clarify the relationships of schizophrenia polygenic risk scores (SZ-PRSs) with a comprehensive array of schizophrenia antecedents and presentations using a culturally and ethnically homogeneous sample of schizophrenia spectrum patients.

METHODS

The top and bottom deciles (n = 172) of the SZ-PRS distribution in a group of 861 patients were compared on information derived from medical records using logistic regression.

RESULTS

High SZ-PRSs were associated with female sex, family history of a wide range of neuropsychiatric conditions, moderately poor premorbid social and cognitive adjustment in childhood, the schizophrenia diagnosis, and positive and "abnormal" psychomotor symptoms. The low-SZ-PRS group demonstrated an accumulation of both individuals with milder forms of SZ spectrum disorders and those with severe premorbid abnormalities in the social, cognitive, and neurological domains.

CONCLUSIONS

The results highlight moderately poor premorbid social and cognitive adjustment as characteristic manifestations of the polygenic component of the schizophrenia etiology and provide the first piece of PRS-based evidence for the long-standing idea of a higher liability threshold in women. The presence of milder and severe cases in the bottom SZ-PRS decile, suggesting its etiological heterogeneity, might be an important source of the inconsistency in the previous research on SZ-PRSs' relationship with schizophrenia phenotypes and should be considered in future studies.

CAMK2; four genes, one syndrome? Delineation of genotype-phenotype correlations

Neurodevelopmental disorders are a heterogenous group of brain disorders impacting cognitive, adaptive, motor, and speech language development. With advancements in diagnostics an increasing number of causative genes are discovered, including synaptic genes. The calcium calmodulin dependent protein kinase type 2 (CAMK2) family is the most abundant kinase family in the synapse and has recently been established to cause NDD, with a growing number of unrelated NDD-individuals who carry pathogenic variations in one of the four CAMK2 genes. However, there is still much to learn about the specific phenotypic manifestations per CAMK2 paralog and per variant type, including the mechanism of how variants in these genes impact CAMK2 protein and synaptic functioning, and result in neurodevelopmental disorders. This review provides an overview of all CAMK2 cases published to date and reveals first genotype-phenotype correlations that can serve as a starting point to explain CAMK2 related symptoms, offering direction for future research.

[Genetic diagnostics of mental health disorders in adulthood]

This review article provides insights into the role of genetic diagnostics in adult mental health disorders. The importance of genetic factors in the development of mental illnesses, from rare genetic syndromes to common complex genetic disorders, is described. Current clinical characteristics that may warrant a genetic diagnostic work-up are highlighted, including intellectual disability, autism spectrum disorders and severe psychiatric conditions with specific comorbidities, such as organ malformations or epilepsy. The review discusses when genetic diagnostics are recommended according to current guidelines as well as situations where they might be considered even in the absence of explicit guideline recommendations. This is followed by an overview of the procedures and the currently used diagnostic methods. Current limitations and possible developments in the field of genetic diagnostics in psychiatry are discussed, including the fact that, for many mental health conditions, genetic testing is not yet part of standard clinical practice; however, in summary genetic causes should be considered more frequently in certain clinical constellations, and genetic diagnostics and counselling should be offered where appropriate.

Deciphering the Pathophysiological Mechanisms Underpinning Myoclonus Dystonia Using Pluripotent Stem Cell-Derived Cellular Models

Dystonia is a movement disorder with an estimated prevalence of 1.2% and is characterised by involuntary muscle contractions leading to abnormal postures and pain. Only symptomatic treatments are available with no disease-modifying or curative therapy, in large part due to the limited understanding of the underlying pathophysiology. However, the inherited monogenic forms of dystonia provide an opportunity for the development of disease models to examine these mechanisms. Myoclonus Dystonia, caused by SGCE mutations encoding the ε-sarcoglycan protein, represents one of now >50 monogenic forms. Previous research has implicated the involvement of the basal ganglia-cerebello-thalamo-cortical circuit in dystonia pathogenesis, but further work is needed to understand the specific molecular and cellular mechanisms. Pluripotent stem cell technology enables a patient-derived disease modelling platform harbouring disease-causing mutations. In this review, we discuss the current understanding of the aetiology of Myoclonus Dystonia, recent advances in producing distinct neuronal types from pluripotent stem cells, and their application in modelling Myoclonus Dystonia in vitro. Future research employing pluripotent stem cell-derived cellular models is crucial to elucidate how distinct neuronal types may contribute to dystonia and how disruption to neuronal function can give rise to dystonic disorders.

Brain organoids: A new tool for modelling of neurodevelopmental disorders

Neurodevelopmental disorders are mostly studied using mice as models. However, the mouse brain lacks similar cell types and structures as those of the human brain. In recent years, emergence of three-dimensional brain organoids derived from human embryonic stem cells or induced pluripotent stem cells allows for controlled monitoring and evaluation of early neurodevelopmental processes and has opened a window for studying various aspects of human brain development. However, such organoids lack original anatomical structure of the brain during maturation, and neurodevelopmental maturation processes that rely on unique cellular interactions and neural network connections are limited. Consequently, organoids are difficult to be used extensively and effectively while modelling later stages of human brain development and disease progression. To address this problem, several methods and technologies have emerged that aim to enhance the sophisticated regulation of brain organoids developmental processes through bioengineering approaches, which may alleviate some of the current limitations. This review discusses recent advances and application areas of human brain organoid culture methods, aiming to generalize optimization strategies for organoid systems, improve the ability to mimic human brain development, and enhance the application value of organoids.

Pathogenic genes implicated in sleep-related hypermotor epilepsy: a research progress update

Sleep-related hypermotor epilepsy (SHE) is a focal epilepsy syndrome characterized by a variable age of onset and heterogeneous etiology. Current literature suggests a prevalence rate of approximately 1.8 per 100,000 persons. The discovery of additional pathogenic genes associated with SHE in recent years has significantly expanded the knowledge and understanding of its pathophysiological mechanisms. Identified SHE pathogenic genes include those related to neuronal ligand- and ion-gated channels (CHRNA4, CHRNB2, CHRNA2, GABRG2, and KCNT1), genes upstream of the mammalian target of rapamycin complex 1 signal transduction pathway (DEPDC5, NPRL2, NPRL3, TSC1, and TSC2), and other genes (CRH, CaBP4, STX1B, and PRIMA1). These genes encode proteins associated with ion channels, neurotransmitter receptors, cell signal transduction, and synaptic transmission. Mutations in these genes can result in the dysregulation of encoded cellular functional proteins and downstream neuronal dysfunction, ultimately leading to epileptic seizures. However, the associations between most genes and the SHE phenotype remain unclear. This article presents a literature review on the research progress of SHE-related pathogenic genes to contribute evidence to genotype-phenotype correlations in SHE and establish the necessary theoretical basis for future SHE treatments.

Historical review: The golden age of the Golgi method in human neuropathology

Golgi methods were used to study human neuropathology in the 1970s, 1980s, and 1990s of the last century. Although a relatively small number of laboratories applied these methods, their impact was crucial by increasing knowledge about: (1) the morphology, orientation, and localization of neurons in human cerebral and cerebellar malformations and ganglionic tumors, and (2) the presence of abnormal structures including large and thin spines (spine dysgenesis) in several disorders linked to mental retardation, focal enlargements of the axon hillock and dendrites (meganeurites) in neuronal storage diseases, growth cone-like appendages in Alzheimer disease, as well as abnormal structures in other dementias. Although there were initial concerns about their reliability, reduced dendritic branches and dendritic spines were identified as common alterations in mental retardation, dementia, and other pathological conditions. Similar observations in appropriate experimental models have supported many abnormalities that were first identified using Golgi methods in human material. Moreover, electron microscopy, immunohistochemistry, fluorescent tracers, and combined methods have proven the accuracy of pioneering observations uniquely visualized as 3D images of fully stained individual neurons. Although Golgi methods had their golden age many years ago, these methods may still be useful complementary tools in human neuropathology.

CHD8-related disorders redefined: an expanding spectrum of dystonic phenotypes

BACKGROUND

Heterozygous loss-of-function variants in CHD8 have been associated with a syndromic neurodevelopmental-disease spectrum, collectively referred to as CHD8-related neurodevelopmental disorders. Several different clinical manifestations, affecting neurodevelopmental and systemic domains, have been described, presenting with highly variable expressivity. Some expressions are well established and comprise autism spectrum disorders, psychomotor delay with cognitive impairment, postnatal overgrowth with macrocephaly, structural brain abnormalities, gastrointestinal disturbances, and behavioral and sleep-pattern problems. However, the complete phenotypic spectrum of CHD8-related disorders is still undefined. In 2021, our group described two singular female patients with CHD8-related neurodevelopmental disorder and striking dystonic manifestations, prompting the suggestion that dystonia should be considered a possible component of this condition.

CASE SERIES PRESENTATION

We describe three additional unrelated female individuals, each carrying a different CHD8 frameshift variant and whose clinical presentations were primarily characterized by young-onset dystonia. Their dystonic manifestations were remarkably heterogeneous and ranged from focal, exercise-dependent, apparently isolated forms to generalized permanent phenotypes accompanied by spasticity and tremor. Neurocognitive impairment and autistic behaviors, typical of CHD8-related disorders, were virtually absent or at the mild end of the spectrum.

CONCLUSIONS

This work validates our previous observation that dystonia is part of the phenotypic spectrum of CHD8-related neurodevelopmental disorders with potential female preponderance, raising new challenges and opportunities in the diagnosis and management of this condition. It also highlights the importance of in-depth neurologic phenotyping of patients carrying variants associated with neurodevelopmental disorders, as the connection between neurodevelopmental and movement disorders is proving closer than previously appreciated.