Disturbed chromosome segregation and multipolar spindle formation in a patient with CHAMP1 mutation

Study of genotoxic and cytotoxic effects induced in human fibroblasts by exposure to pulsed and continuous 1.6 GHz radiofrequency

Background

The widespread use of radiofrequency (RF) sources, ranging from household appliances to telecommunications devices and military equipment, raises concerns among people and regulatory agencies about the potential health risks of RF exposure. Consequently, several in vitro and in vivo studies have been done to investigate the biological effects, in particular non-thermal, of this non-ionizing radiation. To date, this issue is still being debated due to the controversial results that have been reported. Furthermore, the impact of different RF signal modulations on biological systems remains poorly investigated. The present in vitro study aims to evaluate the cytotoxicity and genotoxicity of continuous or pulsed 1.6 GHz RF in human dermal fibroblasts (HDF).

Methods

HDF cultures were exposed to continuous and pulsed 1.6 GHz RF, for 2 h, with Specific Absorption Rate (SAR) of 0.4 W/kg. The potential biological effects of 1.6 GHz RF on HDF were assessed with a multi-methodological approach, analyzing the effects on cell cycle, ultrastructure, protein expression, mitotic spindle, CREST stained micronuclei, chromosome segregation and γ-H2AX/53BP1 foci.

Results

1.6 GHz RF exposure modified proteins expression and morphology of HDF. Specifically, the expression of different heat-shock proteins (HSP) (i.e., HSP-90, HSP-60, and HSP-25) and phospho-AKT were affected. In addition, both continuous and pulsed RF modified the cytoskeletal organization in HDF and increased the number of lysosomes, while the formation of autophagosomes was observed only after pulsed RF exposure. Mitotic spindle anomalies were also found after exposure. However, no significant effect was observed on cell cycle, chromosome segregation, CREST-stained micronuclei and γ-H2AX/53BP1 foci.

Conclusion

The results of the present study show the absence of genotoxic damage in 1.6 GHz RF exposed HDF and, although mitotic spindle alterations were observed, they did not have an aneugenic effect. On the other hand, changes in some proteins expression and cell ultrastructure in exposed HDF suggest that RF can potentially induce cell alterations at the morphological and molecular levels.

CHAMP1-Related Disorder: Sharing 20 Years of thorough Clinical Follow-Up and Review of the Literature

Intellectual disability (ID) is a prevalent neurodevelopmental disorder characterized by limitations in intellectual functioning and adaptive behavior. While the causes of ID are still largely unknown, it is believed to result from a combination of environmental exposures and genetic abnormalities. Recent advancements in genomic studies and clinical genetic testing have identified numerous genes associated with neurodevelopmental disorders (NDDs), including ID. One such gene is CHAMP1, which plays a role in chromosome alignment and has been linked to a specific type of NDD called CHAMP1 disease. This report presents the case of a 21-year-old Lebanese female patient with a de novo mutation in CHAMP1. In addition to ID and NDD, the patient exhibited various clinical features such as impaired language, dysmorphic features, macrocephaly, thoracic hyperkyphosis, decreased pain sensation, and metabolic syndrome. These findings expand the understanding of the clinical spectrum associated with CHAMP1 mutations and highlight the importance of comprehensive follow-up for improved prognosis. Overall, this case contributes to the knowledge of CHAMP1-related NDDs by describing additional clinical features associated with a CHAMP1 mutation. The findings underscore the need for accurate diagnosis, thorough follow-up, and personalized care for individuals with CHAMP1 mutations to optimize their prognosis.

DENND2B activates Rab35 at the intercellular bridge, regulating cytokinetic abscission and tetraploidy

Cytokinesis relies on membrane trafficking pathways regulated by Rabs and guanine nucleotide exchange factors (GEFs). During cytokinesis, the intercellular cytokinetic bridge (ICB) connecting daughter cells undergoes abscission, which requires actin depolymerization. Rab35 recruits MICAL1 to oxidize and depolymerize actin filaments. We show that DENND2B, a protein linked to cancer and congenital disorders, functions as a Rab35 GEF, recruiting and activating Rab35 at the ICB. DENND2B's N-terminal region also interacts with an active form of Rab35, suggesting that DENND2B is both a Rab35 GEF and effector. Knockdown of DENND2B delays abscission, leading to multinucleated cells and filamentous actin (F-actin) accumulation at the ICB, impairing recruitment of ESCRT-III at the abscission site. Additionally, F-actin accumulation triggers the formation of a chromatin bridge, activating the NoCut/abscission checkpoint, and DENND2B knockdown activates Aurora B kinase, a hallmark of checkpoint activation. Thus, our study identifies DENND2B as a crucial player in cytokinetic abscission.

CHAMP1-related disorders: pathomechanisms triggered by different genomic alterations define distinct nosological categories

Loss-of-function variants in CHAMP1 were recently described as cause of a neurodevelopmental disorder characterized by intellectual disability (ID), autism, and distinctive facial characteristics. By exome sequencing (ES), we identified a truncating variant in CHAMP1, c.1858A > T (p.Lys620*), in a patient who exhibited a similar phenotype of severe ID and dysmorphisms. Whether haploinsufficiency or a dominant negative effect is the underlying pathomechanism in these cases is a question that still needs to be addressed. By array-CGH, we detected a 194 kb deletion in 13q34 encompassing CHAMP1, CDC16 and UPF3, in another patient who presented with borderline neurodevelopmental impairment and with no dysmorphisms. In a further patient suffering from early onset refractory seizures, we detected by ES a missense variant in CHAMP1, c.67 G > A (p.Gly23Ser). Genomic abnormalities were all de novo in our patients. We reviewed the clinical and the genetic data of patients reported in the literature with: loss-of-function variants in CHAMP1 (total 40); chromosome 13q34 deletions ranging from 1.1 to 4 Mb (total 7) and of the unique patient with a missense variant. We could infer that loss-of-function variants in CHAMP1 cause a homogeneous phenotype with severe ID, autism spectrum disorders (ASD) and highly distinctive facial characteristics through a dominant negative effect. CHAMP1 haploinsufficiency results in borderline ID with negligible consequences on the quality of life. Missense variants give rise to a severe epileptic encephalopathy through gain-of-function mechanism, most likely. We tentatively define for the first time distinct categories among the CHAMP1-related disorder on the basis of pathomechanisms.

Chromodomain on Y-like 2 (CDYL2) implicated in mitosis and genome stability regulation via interaction with CHAMP1 and POGZ

Histone H3 trimethylation on lysine 9 (H3K9me3) is a defining feature of mammalian pericentromeres, loss of which results in genome instability. Here we show that CDYL2 is recruited to pericentromeres in an H3K9me3-dependent manner and is required for faithful mitosis and genome stability. CDYL2 RNAi in MCF-7 breast cancer cells and Hela cervical cancer cells inhibited their growth, induced apoptosis, and provoked both nuclear and mitotic aberrations. Mass spectrometry analysis of CDYL2-interacting proteins identified the neurodevelopmental disease-linked mitotic regulators CHAMP1 and POGZ, which are associated with a central non-conserved region of CDYL2. RNAi rescue assays identified both the CDYL2 chromodomain and the CHAMP1-POGZ interacting region as required and, together, sufficient for CDYL2 regulation of mitosis and genome stability. CDYL2 RNAi caused loss of CHAMP1 localization at pericentromeres. We propose that CDYL2 functions as an adaptor protein that connects pericentromeric H3K9me3 with CHAMP1 and POGZ to ensure mitotic fidelity and genome stability.

Deficiency of CHAMP1, a gene related to intellectual disability, causes impaired neuronal development and a mild behavioural phenotype

CHAMP1 is a gene associated with intellectual disability, which was originally identified as being involved in the maintenance of kinetochore–microtubule attachment. To explore the neuronal defects caused by CHAMP1 deficiency, we established mice that lack CHAMP1. Mice that are homozygous knockout for CHAMP1 were slightly smaller than wild-type mice and died soon after birth on pure C57BL/6J background. Although gross anatomical defects were not found in CHAMP1^−/− mouse brains, mitotic cells were increased in the cerebral cortex. Neuronal differentiation was delayed in CHAMP1^−/− neural stem cells in vitro, which was also suggested in vivo by CHAMP1 knockdown. In a behavioural test battery, adult CHAMP1 heterozygous knockout mice showed mild memory defects, altered social interaction, and depression-like behaviours. In transcriptomic analysis, genes related to neurotransmitter transport and neurodevelopmental disorder were downregulated in embryonic CHAMP1^−/− brains. These results suggest that CHAMP1 plays a role in neuronal development, and CHAMP1-deficient mice resemble some aspects of individuals with CHAMP1 mutations.

Neurodevelopmental phenotypes in individuals with pathogenic variants in CHAMP1

De novo pathogenic variants in CHAMP1 (chromosome alignment maintaining phosphoprotein 1), which encodes kinetochore-microtubule associated protein on 13q34, cause a rare neurodevelopmental disorder. We enrolled 14 individuals with pathogenic variants in CHAMP1 that were documented by exome sequencing or gene panel sequencing. Medical history interviews, seizure surveys, Vineland Adapted Behavior Scales Second Edition, and other behavioral surveys were completed by primary caregivers of available participants in Simons Searchlight. Clinicians extracted clinical data from the medical record for two participants. We report on clinical features of 14 individuals (ages 2-26) with de novo predicted loss-of-function variants in CHAMP1 and compare them with previously reported cases (total n = 32). At least two individuals have the same de novo variant: p.(Ser181Cysfs*5), p.(Trp348*), p.(Arg398*), p.(Arg497*), or p.(Tyr709*). Common phenotypes include intellectual disability/developmental delay, language impairment, congenital and acquired microcephaly, behavioral problems including autism spectrum disorder, seizures, hypotonia, gastrointestinal issues of reflux and constipation, and ophthalmologic issues. Other rarely observed phenotypes include leukemia, failure to thrive, and high pain tolerance. Pathogenic variants in CHAMP1 are associated with a variable clinical phenotype of developmental delay/intellectual disability and seizures.

First Chinese patient with mental retardation-40 due to a de novo CHAMP1 frameshift mutation: Case report and literature review

Mental retardation-40 (MRD40) is a rare autosomal dominant neurodevelopmental disorder with a poor prognosis that is caused by a heterozygous mutation in chromosome alignment maintaining phosphoprotein 1 (CHAMP1). It was previously considered a non-syndromic disease due to the lack of specific external features. Only limited international reports describing CHAMP1 mutations are currently available. The present case study was the first to report on a Chinese patient with MRD40. The patient presented with severe global development delay with significant craniofacial dysmorphia. Using trio whole-exome sequencing, a novel de novo frameshift mutation in CHAMP1, NM_032436.2: c.530delCinsTTT, was identified, which expands the spectrum of the known pathogenic variants. The present case report helps to improve the syndromic profile of the rare MRD40 disorder and provides an example for the clinical diagnosis of MRD40.

[Autosomal dominant intellectual disability-40 caused by a de novo mutation of the CHAMP1 gene: a case report]

A boy, aged 6 months, had the manifestations of intellectual and motor developmental delay, head instability, general weakness, unawareness of grasping objects by hands, and unusual facies (slightly wide eye distance, epicanthus, esotropia, mouth-opening appearance, short philtrum, and low-set ears). Gene detection results showed a de novo heterozygous frameshift mutation of the CHAMP1 gene at the chromosomal location of chr13:115089847, and nuclear acid was changed to c.530delCinsTTT, resulting in a change in amino acid to p.S177Ffs*2. Therefore, the boy was diagnosed with autosomal dominant intellectual disability-40 caused by the mutation in the CHAMP1 gene. This case report suggests that for children with unexplained intellectual disability, especially those with generalized hypotonia and severe language disorder, the possibility of CHAMP1 gene mutation should be considered, and genetic testing should be performed as early as possible.

Disturbed chromosome segregation and multipolar spindle formation in a patient with CHAMP1 mutation

Background

Patients with intellectual disability (ID) typically exhibit significant defects in both intelligence and adaptive behavior. Aberration of several genes involved in proper progression of mitosis has been reported to underlie ID. Here, we report a new patient with a novel mutation of CHAMP1.

Methods

Whole exome sequencing (WES) analysis was performed. We isolated lymphoblast cells from the CHAMP1 patient and observed chromosome segregation.

Results

We identified a de novo frameshift mutation in CHAMP1. We find that these cells exhibit an increase in centrosome number and resulting multipolar spindle formation. The phenotypes observed in the patient's lymphoblastoid cells were presumably because of cytokinesis failure. We also confirm the identical phenotypes in human culture cells depleted of CHAMP1.

Conclusion

CHAMP1 encodes a protein regulating kinetochore–microtubule attachment and chromosome segregation. These data strongly support that CHAMP1 mutations cause ID, and suggest that CHAMP1 is critical for progression of cytokinesis and maintenance of centrosome number.