De Novo Missense Substitutions in the Gene Encoding CDK8, a Regulator of the Mediator Complex, Cause a Syndromic Developmental Disorder

Manifold functions of Mediator complex in neurodevelopmental disorders

Neurodevelopmental disorders (NDDs) encompass a diverse range of impairments affecting brain development and functions, often presenting as deficits in motor skills, cognitive abilities, language development and neuropsychiatric health. The emergence of next-generation sequencing has unveiled numerous genetic variants linked to NDDs, implicating molecular pathways involved in essential neuronal processes such as synaptic plasticity, neuronal architecture and proteostasis. Central to these processes is the Mediator complex, a highly conserved multi-subunit assembly crucial for RNA polymerase II (Pol II)-dependent transcription. The Mediator functions as a key regulator of gene expression, playing a pivotal role in coordinating cellular processes essential for neuronal differentiation and developmental signaling cascades. Increasingly evidence has shown that its dysfunction is highly associated with the pathogenesis of NDDs. This review aims to comprehensively examine the structural and functional characteristics of individual mediator subunits. We will focus on clinical case reports and recent preclinical studies that highlight the connection between genetic abnormalities in the Mediator complex and specific neurodevelopmental phenotypes, ultimately guiding the development of enhanced diagnostic tools and therapeutic interventions. Furthermore, this review will advance our understanding of the general role transcriptional regulation plays in the etiology of NDDs.

Quitting Your Day Job in Response to Stress: Cell Survival and Cell Death Require Secondary Cytoplasmic Roles of Cyclin C and Med13

Following unfavorable environmental cues, cells reprogram pathways that govern transcription, translation, and protein degradation systems. This reprogramming is essential to restore homeostasis or commit to cell death. This review focuses on the secondary roles of two nuclear transcriptional regulators, cyclin C and Med13, which play key roles in this decision process. Both proteins are members of the Mediator kinase module (MKM) of the Mediator complex, which, under normal physiological conditions, positively and negatively regulates a subset of stress response genes. However, cyclin C and Med13 translocate to the cytoplasm following cell death or cell survival cues, interacting with a host of cell death and cell survival proteins, respectively. In the cytoplasm, cyclin C is required for stress-induced mitochondrial hyperfission and promotes regulated cell death pathways. Cytoplasmic Med13 stimulates the stress-induced assembly of processing bodies (P-bodies) and is required for the autophagic degradation of a subset of P-body assembly factors by cargo hitchhiking autophagy. This review focuses on these secondary, a.k.a. "night jobs" of cyclin C and Med13, outlining the importance of these secondary functions in maintaining cellular homeostasis following stress.

Bi-allelic MED16 variants cause a MEDopathy with intellectual disability, motor delay, and craniofacial, cardiac, and limb malformations

The Mediator complex regulates protein-coding gene transcription by coordinating the interaction of upstream enhancers with the basal transcription machinery at the promoter. Pathogenic variants in Mediator subunits typically lead to neurodevelopmental or neurodegenerative disorders with variable clinical presentations, designated as MEDopathies. Here, we report the identification of 25 individuals from 18 families with bi-allelic MED16 variants who have a multiple congenital anomalies (MCAs)-intellectual disability syndrome. Intellectual disability, speech delay, and/or motor delay of variable severity were constant and associated with variable combinations of craniofacial defects (micro/retrognathia, cleft palate, and preauricular tags), anomalies of the extremities, and heart defects (predominantly tetralogy of Fallot). Visual impairment, deafness, and magnetic resonance imaging (MRI) abnormalities were also frequent. The 26 variants identified were comprised of eight predicted protein-truncating (three intragenic deletions, two frameshifts, and one nonsense and two essential splice site variants) and 18 missense or in-frame duplication variants affecting conserved residues, without clear correlation between phenotypic severity and variant type combination. Three-dimensional modeling indicated that the missense and duplication variants likely have a destabilizing effect on the structural elements of the protein. Immunofluorescence assays demonstrated protein mislocalization from the nucleus to the cytoplasm for 16 of the 17 variants studied. Homozygous mutant med16 zebrafish presented growth delay and increased mortality compared with wild-type fish, and Med16 knockout mice are preweaning lethal, highlighting the conserved requirement of MED16 for development. Overall, we describe an autosomal recessive MCAs-intellectual disability MEDopathy, emphasizing the importance of Mediator during neurodevelopment and suggesting that some tissues are particularly sensitive to the loss of certain subunits.

Cyclin-dependent protein kinases and cell cycle regulation in biology and disease

Cyclin Dependent Kinases (CDKs) are closely connected to the regulation of cell cycle progression, having been first identified as the kinases able to drive cell division. In reality, the human genome contains 20 different CDKs, which can be divided in at least three different sub-family with different functions, mechanisms of regulation, expression patterns and subcellular localization. Most of these kinases play fundamental roles the normal physiology of eucaryotic cells; therefore, their deregulation is associated with the onset and/or progression of multiple human disease including but not limited to neoplastic and neurodegenerative conditions. Here, we describe the functions of CDKs, categorized into the three main functional groups in which they are classified, highlighting the most relevant pathways that drive their expression and functions. We then discuss the potential roles and deregulation of CDKs in human pathologies, with a particular focus on cancer, the human disease in which CDKs have been most extensively studied and explored as therapeutic targets. Finally, we discuss how CDKs inhibitors have become standard therapies in selected human cancers and propose novel ways of investigation to export their targeting from cancer to other relevant chronic diseases. We hope that the effort we made in collecting all available information on both the prominent and lesser-known CDK family members will help in identify and develop novel areas of research to improve the lives of patients affected by debilitating chronic diseases.

Brain volume in infants with metopic synostosis: Less white matter volume with an accelerated growth pattern in early life

Metopic synostosis patients are at risk for neurodevelopmental disorders despite a negligible risk of intracranial hypertension. To gain insight into the underlying pathophysiology of metopic synostosis and associated neurodevelopmental disorders, we aimed to investigate brain volumes of non-syndromic metopic synostosis patients using preoperative MRI brain scans. MRI brain scans were processed with HyperDenseNet to calculate total intracranial volume (TIV), total brain volume (TBV), total grey matter volume (TGMV), total white matter volume (TWMV) and total cerebrospinal fluid volume (TCBFV). We compared global brain volumes of patients with controls corrected for age and sex using linear regression. Lobe-specific grey matter volumes were assessed in secondary analyses. We included 45 metopic synostosis patients and 14 controls (median age at MRI 0.56 years [IQR 0.36] and 1.1 years [IQR 0.47], respectively). We found no significant differences in TIV, TBV, TGMV or TCBFV in patients compared to controls. TWMV was significantly smaller in patients (-62,233 mm3 [95% CI = -96,968; -27,498], Holm-corrected p = 0.004), and raw data show an accelerated growth pattern of white matter in metopic synostosis patients. Grey matter volume analyses per lobe indicated increased cingulate (1378 mm3 [95% CI = 402; 2355]) and temporal grey matter (4747 [95% CI = 178; 9317]) volumes in patients compared to controls. To conclude, we found smaller TWMV with an accelerated white matter growth pattern in metopic synostosis patients, similar to white matter growth patterns seen in autism. TIV, TBV, TGMV and TCBFV were comparable in patients and controls. Secondary analyses suggest larger cingulate and temporal lobe volumes. These findings suggest a generalized intrinsic brain anomaly in the pathophysiology of neurodevelopmental disorders associated with metopic synostosis.

Novel insights into the phenotypic spectrum and pathogenesis of Hardikar syndrome

PURPOSE

Hardikar syndrome (HS, MIM #301068) is a female-specific multiple congenital anomaly syndrome characterized by retinopathy, orofacial clefting, aortic coarctation, biliary dysgenesis, genitourinary malformations, and intestinal malrotation. We previously showed that heterozygous nonsense and frameshift variants in MED12 cause HS. The phenotypic spectrum of disease and the mechanism by which MED12 variants cause disease is unknown. We aim to expand the phenotypic and molecular landscape of HS and elucidate the mechanism by which MED12 variants cause disease.

METHODS

We clinically assembled and molecularly characterized a cohort of 11 previously unreported individuals with HS. Additionally, we studied the effect of MED12 deficiency on ciliary biology, hedgehog, and yes-associated protein (YAP) signaling; pathways implicated in diseases with phenotypic overlap with HS.

RESULTS

We report novel phenotypes associated with HS, including cardiomyopathy, arrhythmia, and vascular anomalies, and expand the molecular landscape of HS to include splice site variants. We additionally demonstrate that MED12 deficiency causes decreased cell ciliation, and impairs hedgehog and YAP signaling.

CONCLUSION

Our data support updating HS standard-of-care to include regular cardiac imaging, arrhythmia screening, and vascular imaging. We further propose that dysregulation of ciliogenesis and YAP and hedgehog signaling contributes to the pathogenesis of HS.

Mediator complex in transcription regulation and DNA repair: Relevance for human diseases

The Mediator complex is an essential coregulator of RNA polymerase II transcription. More recent developments suggest Mediator functions as a link between transcription regulation, genome organisation and DNA repair mechanisms including nucleotide excision repair, base excision repair, and homologous recombination. Dysfunctions of these processes are frequently associated with human pathologies, and growing evidence shows Mediator involvement in cancers, neurological, metabolic and infectious diseases. The detailed deciphering of molecular mechanisms of Mediator functions, using interdisciplinary approaches in different biological models and considering all functions of this complex, will contribute to our understanding of relevant human diseases.

A de novo frameshift variant in MED13 gene in a patient with autism spectrum disorder and magnetic resonance imaging abnormalities mimicking tuberous sclerosis

The mediator complex subunit 13 (MED13) gene is implicated in neurodevelopmental disorders including autism spectrum disorder (ASD), intellectual disability, and speech delay with varying severity and course. Additional, extra central nervous system, features include eye or vision problems, hypotonia, congenital heart abnormalities, and dysmorphisms. We describe a 7-year- and 4-month-old girl evaluated for ASD whose brain magnetic resonance imaging was suggestive of multiple cortical tubers. The exome sequencing (ES - trio analysis) uncovered a unique, de novo, frameshift variant in the MED13 gene (c.4880del, D1627Vfs*17), with a truncating effect on the protein. This case report thus expands the phenotypic spectrum of MED13-related disorders to include brain abnormalities.

Expanding phenotype of MED13-associated syndrome presenting novel de novo missense variant in a patient with multiple congenital anomalies

BACKGROUND

Whole exome sequencing allows rapid identification of causative single nucleotide variants and short insertions/deletions in children with congenital anomalies and/or intellectual disability, which aids in accurate diagnosis, prognosis, appropriate therapeutic interventions, and family counselling. Recently, de novo variants in the MED13 gene were described in patients with an intellectual developmental disorder that included global developmental delay, mild congenital heart anomalies, and hearing and vision problems in some patients.

RESULTS

Here we describe an infant who carried a de novo p.Pro835Ser missense variant in the MED13 gene, according to whole exome trio sequencing. He presented with congenital heart anomalies, dysmorphic features, hydrocephalic changes, hypoplastic corpus callosum, bilateral optic nerve atrophy, optic chiasm atrophy, brain stem atrophy, and overall a more severe condition compared to previously described patients.

CONCLUSIONS

Therefore, we propose to expand the MED13-associated phenotype to include severe complications that could end up with multiple organ failure and neonatal death.

MED13 Gene Mutation Related to Autism Spectrum Disorder: A Case Report

This case report highlights an association between the MED13 gene and autism spectrum disorder (ASD). ASD is a neurodevelopmental disorder characterized by impaired social interactions, communication difficulties, and repetitive behaviors. The MED13 gene encodes a subunit of the Mediator complex, which plays a key role in gene expression regulation and transcriptional processes. In this case report, we present a case of a child diagnosed with ASD who underwent whole exome sequencing (WES) and revealed an uncertain heterozygous variant in the MED13 gene. The patient exhibited typical features of ASD, including the following: social and communication deficits, restricted interests, repetitive behaviors, and characteristic dysmorphic facial features. The identification of this MED13 gene variant provides further evidence of its potential involvement in ASD pathogenesis. This case adds to the growing body of evidence linking MED13 gene mutations to ASD susceptibility. Understanding the genetic basis of ASD through case reports can aid in early diagnosis, personalized treatment strategies, and genetic counseling for affected individuals and their families. Further research is warranted to explain the precise mechanisms underlying MED13 gene involvement in ASD.

Expanding the phenotypic spectrum for CDK8-related disease: A case report

BACKGROUND

Cyclin-dependent kinase 8 (CDK8) is part of a regulatory kinase module that regulates the activity of the Mediator complex. The Mediator, a large conformationally flexible protein complex, goes on to regulate RNA polymerase II activity, consequently affecting transcriptional regulation. Thus, inactivating mutations of the genes within the kinase module cause aberrant transcriptional regulation and disease, namely, CDK8-related intellectual developmental disorder with hypotonia and behavioral abnormalities (IDDHBA).

CASE PRESENTATION

We describe, for the first time, a likely pathogenic heterozygous CDK8 variant c.599G>A, p.(Arg200Gln) inherited from the biological mother. The clinical presentation of the child and mother is within the described clinical spectrum for IDDHBA; however, undocumented progressive contractures of the hips and knees as well as scoliosis were also observed in the child. This phenotype was not found in the mother, highlighting a heterogenous presentation for the same variant within the same family. Furthermore, the described clinical presentation may further support the notion of a module- or Mediator-related syndrome with varying clinical presentation.

CONCLUSION

This case report documents the first inherited case of IDDHBA and expands the phenotypic spectrum for CDK8-related disease to include undocumented progressive contractures of the hips and knees as well as scoliosis, which may support the notion of a module- or Mediator-related syndrome with varying clinical presentation.

Cdk8/CDK19 promotes mitochondrial fission through Drp1 phosphorylation and can phenotypically suppress pink1 deficiency in Drosophila

Cdk8 in Drosophila is the orthologue of vertebrate CDK8 and CDK19. These proteins have been shown to modulate transcriptional control by RNA polymerase II. We found that neuronal loss of Cdk8 severely reduces fly lifespan and causes bang sensitivity. Remarkably, these defects can be rescued by expression of human CDK19, found in the cytoplasm of neurons, suggesting a non-nuclear function of CDK19/Cdk8. Here we show that Cdk8 plays a critical role in the cytoplasm, with its loss causing elongated mitochondria in both muscles and neurons. We find that endogenous GFP-tagged Cdk8 can be found in both the cytoplasm and nucleus. We show that Cdk8 promotes the phosphorylation of Drp1 at S616, a protein required for mitochondrial fission. Interestingly, Pink1, a mitochondrial kinase implicated in Parkinson's disease, also phosphorylates Drp1 at the same residue. Indeed, overexpression of Cdk8 significantly suppresses the phenotypes observed in flies with low levels of Pink1, including elevated levels of ROS, mitochondrial dysmorphology, and behavioral defects. In summary, we propose that Pink1 and Cdk8 perform similar functions to promote Drp1-mediated fission.

Cochleovestibular Phenotype in a Rare Genetic MED13L Mutation

The gene MED13 participates in transcription. The MED13L gene is a paralog of MED13 that is involved in developmental gene expression. Mutations in the gene have been shown to result in a heterogenous phenotype affecting several physiological systems. Hearing loss has been reported very rarely, and vestibular weakness has never been reported in the condition. In this report, we present a mutation of MED13L in c.1162A > T (p.Arg388Ter), where we detail and describe a cochleovestibular phenotype with objective vestibulometry for the first time. The child showed bilateral sloping sensorineural hearing loss, a bilateral vestibular weakness, and an inner ear vestibular structural abnormality on imaging. Early intervention with hearing aids and vestibular rehabilitation led to a favorable outcome in terms of speech, communication, and balance. We emphasize the importance of comprehensive audiovestibular assessment in children diagnosed with MED13L mutations for effective management of these children.

Biallelic MED27 variants lead to variable ponto-cerebello-lental degeneration with movement disorders

MED27 is a subunit of the Mediator multiprotein complex, which is involved in transcriptional regulation. Biallelic MED27 variants have recently been suggested to be responsible for an autosomal recessive neurodevelopmental disorder with spasticity, cataracts and cerebellar hypoplasia. We further delineate the clinical phenotype of MED27-related disease by characterizing the clinical and radiological features of 57 affected individuals from 30 unrelated families with biallelic MED27 variants. Using exome sequencing and extensive international genetic data sharing, 39 unpublished affected individuals from 18 independent families with biallelic missense variants in MED27 have been identified (29 females, mean age at last follow-up 17 ± 12.4 years, range 0.1-45). Follow-up and hitherto unreported clinical features were obtained from the published 12 families. Brain MRI scans from 34 cases were reviewed. MED27-related disease manifests as a broad phenotypic continuum ranging from developmental and epileptic-dyskinetic encephalopathy to variable neurodevelopmental disorder with movement abnormalities. It is characterized by mild to profound global developmental delay/intellectual disability (100%), bilateral cataracts (89%), infantile hypotonia (74%), microcephaly (62%), gait ataxia (63%), dystonia (61%), variably combined with epilepsy (50%), limb spasticity (51%), facial dysmorphism (38%) and death before reaching adulthood (16%). Brain MRI revealed cerebellar atrophy (100%), white matter volume loss (76.4%), pontine hypoplasia (47.2%) and basal ganglia atrophy with signal alterations (44.4%). Previously unreported 39 affected individuals had seven homozygous pathogenic missense MED27 variants, five of which were recurrent. An emerging genotype-phenotype correlation was observed. This study provides a comprehensive clinical-radiological description of MED27-related disease, establishes genotype-phenotype and clinical-radiological correlations and suggests a differential diagnosis with syndromes of cerebello-lental neurodegeneration and other subtypes of 'neuro-MEDopathies'.

Mediator complex in neurological disease

Neurological diseases, including traumatic brain injuries, stroke (haemorrhagic and ischemic), and inherent neurodegenerative diseases cause acquired disability in humans, representing a leading cause of death worldwide. The Mediator complex (MED) is a large, evolutionarily conserved multiprotein that facilities the interaction between transcription factors and RNA Polymerase II in eukaryotes. Some MED subunits have been found altered in the brain, although their specific functions in neurodegenerative diseases are not fully understood. Mutations in MED subunits were associated with a wide range of genetic diseases for MED12, MED13, MED13L, MED20, MED23, MED25, and CDK8 genes. In addition, MED12 and MED23 were deregulated in the Alzheimer's Disease. Interestingly, most of the genomic mutations have been found in the subunits of the kinase module. To date, there is only one evidence on MED1 involvement in post-stroke cognitive deficits. Although the underlying neurodegenerative disorders may be different, we are confident that the signal cascades of the biological-cognitive mechanisms of brain adaptation, which begin after brain deterioration, may also differ. Here, we analysed relevant studies in English published up to June 2023. They were identified through a search of electronic databases including PubMed, Medline, EMBASE and Scopus, including search terms such as "Mediator complex", "neurological disease", "brains". Thematic content analysis was conducted to collect and summarize all studies demonstrating MED alteration to understand the role of this central transcriptional regulatory complex in the brain. Improved and deeper knowledge of the regulatory mechanisms in neurological diseases can increase the ability of physicians to predict onset and progression, thereby improving diagnostic care and providing appropriate treatment decisions.

Pathogenic mutation hotspots in protein kinase domain structure

Control of eukaryotic cellular function is heavily reliant on the phosphorylation of proteins at specific amino acid residues, such as serine, threonine, tyrosine, and histidine. Protein kinases that are responsible for this process comprise one of the largest families of evolutionarily related proteins. Dysregulation of protein kinase signaling pathways is a frequent cause of a large variety of human diseases including cancer, autoimmune, neurodegenerative, and cardiovascular disorders. In this study, we mapped all pathogenic mutations in 497 human protein kinase domains from the ClinVar database to the reference structure of Aurora kinase A (AURKA) and grouped them by the relevance to the disease type. Our study revealed that the majority of mutation hotspots associated with cancer are situated within the catalytic and activation loops of the kinase domain, whereas non-cancer-related hotspots tend to be located outside of these regions. Additionally, we identified a hotspot at residue R371 of the AURKA structure that has the highest number of exclusively non-cancer-related pathogenic mutations (21) and has not been previously discussed.

Pathogenic variants in the paired-related homeobox 1 gene (PRRX1) cause craniosynostosis with incomplete penetrance

PURPOSE

Studies have previously implicated PRRX1 in craniofacial development, including demonstration of murine Prrx1 expression in the preosteogenic cells of the cranial sutures. We investigated the role of heterozygous missense and loss-of-function (LoF) variants in PRRX1 associated with craniosynostosis.

METHODS

Trio-based genome, exome, or targeted sequencing were used to screen PRRX1 in patients with craniosynostosis; immunofluorescence analyses were used to assess nuclear localization of wild-type and mutant proteins.

RESULTS

Genome sequencing identified 2 of 9 sporadically affected individuals with syndromic/multisuture craniosynostosis, who were heterozygous for rare/undescribed variants in PRRX1. Exome or targeted sequencing of PRRX1 revealed a further 9 of 1449 patients with craniosynostosis harboring deletions or rare heterozygous variants within the homeodomain. By collaboration, 7 additional individuals (4 families) were identified with putatively pathogenic PRRX1 variants. Immunofluorescence analyses showed that missense variants within the PRRX1 homeodomain cause abnormal nuclear localization. Of patients with variants considered likely pathogenic, bicoronal or other multisuture synostosis was present in 11 of 17 cases (65%). Pathogenic variants were inherited from unaffected relatives in many instances, yielding a 12.5% penetrance estimate for craniosynostosis.

CONCLUSION

This work supports a key role for PRRX1 in cranial suture development and shows that haploinsufficiency of PRRX1 is a relatively frequent cause of craniosynostosis.

Large-Scale Functional Assessment of Genes Involved in Rare Diseases with Intellectual Disabilities Unravels Unique Developmental and Behaviour Profiles in Mouse Models

Major progress has been made over the last decade in identifying novel genes involved in neurodevelopmental disorders, although the task of elucidating their corresponding molecular and pathophysiological mechanisms, which are an essential prerequisite for developing therapies, has fallen far behind. We selected 45 genes for intellectual disabilities to generate and characterize mouse models. Thirty-nine of them were based on the frequency of pathogenic variants in patients and literature reports, with several corresponding to de novo variants, and six other candidate genes. We used an extensive screen covering the development and adult stages, focusing specifically on behaviour and cognition to assess a wide range of functions and their pathologies, ranging from basic neurological reflexes to cognitive abilities. A heatmap of behaviour phenotypes was established, together with the results of selected mutants. Overall, three main classes of mutant lines were identified based on activity phenotypes, with which other motor or cognitive deficits were associated. These data showed the heterogeneity of phenotypes between mutation types, recapitulating several human features, and emphasizing the importance of such systematic approaches for both deciphering genetic etiological causes of ID and autism spectrum disorders, and for building appropriate therapeutic strategies.

The Mediator complex as a master regulator of transcription by RNA polymerase II

The Mediator complex, which in humans is 1.4 MDa in size and includes 26 subunits, controls many aspects of RNA polymerase II (Pol II) function. Apart from its size, a defining feature of Mediator is its intrinsic disorder and conformational flexibility, which contributes to its ability to undergo phase separation and to interact with a myriad of regulatory factors. In this Review, we discuss Mediator structure and function, with emphasis on recent cryogenic electron microscopy data of the 4.0-MDa transcription preinitiation complex. We further discuss how Mediator and sequence-specific DNA-binding transcription factors enable enhancer-dependent regulation of Pol II function at distal gene promoters, through the formation of molecular condensates (or transcription hubs) and chromatin loops. Mediator regulation of Pol II reinitiation is also discussed, in the context of transcription bursting. We propose a working model for Mediator function that combines experimental results and theoretical considerations related to enhancer-promoter interactions, which reconciles contradictory data regarding whether enhancer-promoter communication is direct or indirect. We conclude with a discussion of Mediator's potential as a therapeutic target and of future research directions.

A Diffusion Tensor Imaging Analysis of Frontal Lobe White Matter Microstructure in Trigonocephaly Patients

BACKGROUND

Children with trigonocephaly are at risk for neurodevelopmental disorders. The aim of this study is to investigate white matter properties of the frontal lobes in young, unoperated patients with metopic synostosis as compared to healthy controls using diffusion tension imaging (DTI).

METHODS

Preoperative DTI data sets of 46 patients with trigonocephaly with a median age of 0.49 (interquartile range: 0.38) years were compared with 21 controls with a median age of 1.44 (0.98) years. White matter metrics of the tracts in the frontal lobe were calculated using FMRIB Software Library (FSL). The mean value of tract-specific fractional anisotropy (FA) and mean diffusivity (MD) were estimated for each subject and compared to healthy controls. By linear regression, FA and MD values per tract were assessed by trigonocephaly, sex, and age.

RESULTS

The mean FA and MD values in the frontal lobe tracts of untreated trigonocephaly patients, younger than 3 years, were not significantly different in comparison to controls, where age showed to be a significant associated factor.

CONCLUSIONS

Microstructural parameters of white matter tracts of the frontal lobe of patients with trigonocephaly are comparable to those of controls aged 0-3 years.

Transcription Pause and Escape in Neurodevelopmental Disorders

Transcription pause-release is an important, highly regulated step in the control of gene expression. Modulated by various factors, it enables signal integration and fine-tuning of transcriptional responses. Mutations in regulators of pause-release have been identified in a range of neurodevelopmental disorders that have several common features affecting multiple organ systems. This review summarizes current knowledge on this novel subclass of disorders, including an overview of clinical features, mechanistic details, and insight into the relevant neurodevelopmental processes.

Aberrant cyclin C nuclear release induces mitochondrial fragmentation and dysfunction in MED13L syndrome fibroblasts

MED13L syndrome is a haploinsufficiency developmental disorder characterized by intellectual disability, heart malformation, and hypotonia. MED13L controls transcription by tethering the cyclin C-Cdk8 kinase module (CKM) to the Mediator complex. In addition, cyclin C has CKM-independent roles in the cytoplasm directing stress-induced mitochondrial fragmentation and regulated cell death. Unstressed MED13L ^{S1497 F/fs} patient fibroblasts exhibited aberrant cytoplasmic cyclin C localization, mitochondrial fragmentation, and a 6-fold reduction in respiration. In addition, the fibroblasts exhibited reduced mtDNA copy number, reduction in mitochondrial membrane integrity, and hypersensitivity to oxidative stress. Finally, transcriptional analysis of MED13L mutant fibroblasts revealed reduced mRNA levels for several genes necessary for normal mitochondrial function. Pharmacological or genetic approaches preventing cyclin C-mitochondrial localization corrected the fragmented mitochondrial phenotype and partially restored organelle function. In conclusion, this study found that mitochondrial dysfunction is an underlying defect in cells harboring the MED13L ^{S1497 F/fs} allele and identified cyclin C mis-localization as the likely cause. These results provide a new avenue for understanding this disorder.

Cerebral Blood Flow of the Frontal Lobe in Untreated Children with Trigonocephaly versus Healthy Controls: An Arterial Spin Labeling Study

BACKGROUND

Craniofacial surgery is the standard treatment for children with moderate to severe trigonocephaly. The added value of surgery to release restriction of the frontal lobes is unproven, however. In this study, the authors aim to address the hypothesis that the frontal lobe perfusion is not restricted in trigonocephaly patients by investigating cerebral blood flow.

METHODS

Between 2018 and 2020, trigonocephaly patients for whom a surgical correction was considered underwent magnetic resonance imaging brain studies with arterial spin labeling to measure cerebral perfusion. The mean value of cerebral blood flow in the frontal lobe was calculated for each subject and compared to that of healthy controls.

RESULTS

Magnetic resonance imaging scans of 36 trigonocephaly patients (median age, 0.5 years; interquartile range, 0.3; 11 female patients) were included and compared to those of 16 controls (median age, 0.83 years; interquartile range, 0.56; 10 female patients). The mean cerebral blood flow values in the frontal lobe of the trigonocephaly patients (73.0 ml/100 g/min; SE, 2.97 ml/100 g/min) were not significantly different in comparison to control values (70.5 ml/100 g/min; SE, 4.45 ml/100 g/min; p = 0.65). The superior, middle, and inferior gyri of the frontal lobe showed no significant differences either.

CONCLUSIONS

The authors' findings suggest that the frontal lobes of trigonocephaly patients aged less than 18 months have a normal cerebral blood flow before surgery. In addition to the very low prevalence of papilledema or impaired skull growth previously reported, this finding further supports the authors' hypothesis that craniofacial surgery for trigonocephaly is rarely indicated for signs of raised intracranial pressure or restricted perfusion for patients younger than 18 months.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Risk, II.

A novel nonsense variant in MED12 associated with malformations in a female fetus

Pathogenic variants in the MED12 gene located on the X-chromosome have primarily been reported in males with Lujan-Fryns syndrome, Ohdo syndrome and the Opits-Kaveggia syndrome. However, earlier reports of female patients and female mice suggest that MED12 deficiency causes severe malformations. We report a novel example of a MED12 de novo nonsense variant in a female fetus with severe malformations identified by trio-exome sequencing. This finding further expands the clinical spectrum of MED12-related disorders, which is vital for prenatal diagnosis and genetic counselling of couples.

Association between CDK8 gene polymorphisms and dilated cardiomyopathy in a Chinese Han population

Background

Dilated cardiomyopathy (DCM) is one of the most common types of cardiomyopathies. Various genes have been verified to be related to DCM, but the pathogenesis remains unclear. Cyclin-dependent-kinase 8 (CDK8), encoded by the CDK8 gene, is a transcriptional factor that regulates the phosphorylation of RNA polymerase II. It plays an important role in the transcription process and different signaling pathways. This study aimed to investigate the potential role of CDK8 gene polymorphisms in DCM susceptibility and prognosis in a Chinese Han population.

Methods

Two single nucleotide polymorphisms (SNPs) of CDK8, rs17083838 (A/G) and rs7992670 (A/G), were genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in 341 DCM patients and 381 healthy controls. Survival analysis was performed using Kaplan-Meier curves and Cox regression analysis.

Results

The frequencies of allele A of both SNPs rs17083838 and rs7992670 were increased in DCM patients compared to healthy controls (P<0.05). Genotypic frequencies of rs17083838 and rs7992670 were associated with the susceptibility to DCM in the codominant, and recessive models (P<0.05), and AA/AG genotypes of rs17083838 were also related to DCM susceptibility in the dominant model. AA/AG genotypes of rs17083838 and the AA genotype of rs7992670 in the dominant and recessive genetic models presented a correlation with the poor prognosis of DCM patients in both univariate (P<0.05) and multivariate analyses (P<0.05) after adjusting for age, gender, left ventricular end-diastolic diameter (LVEDD), and left ventricular ejection fraction (LVEF).

Conclusions

This research is the first to reveal that CDK8 gene polymorphisms might be related to DCM susceptibility and prognosis in the Chinese Han population.

Increased unfolded protein responses caused by MED17 mutations

Mediator (MED) is a key regulator of protein-coding gene expression, and mutations in MED subunits are associated with a broad spectrum of diseases. Because mutations in MED17 result in autosomal recessive disorders, including microcephaly, intellectual disability, epilepsy, and ataxia, which are barely reported, with only three case reports to date, genotype-phenotype association should be elucidated. Here, we investigated the impact of MED17 mutations on cellular responses and found increased unfolded protein responses (UPRs) in fibroblasts derived from Japanese patients with MED17 mutations. The expression of the UPR genes CHOP and ATF4 was upregulated, and the phosphorylation of eIF2a was basally increased in patients' cells. Based on our findings, we propose that increased UPRs caused by MED17 mutations might contribute to the clinical phenotype.

CDK19-related disorder results from both loss-of-function and gain-of-function de novo missense variants

PURPOSE

To expand the recent description of a new neurodevelopmental syndrome related to alterations in CDK19.

METHODS

Individuals were identified through international collaboration. Functional studies included autophosphorylation assays for CDK19 Gly28Arg and Tyr32His variants and in vivo zebrafish assays of the CDK19G28R and CDK19Y32H.

RESULTS

We describe 11 unrelated individuals (age range: 9 months to 14 years) with de novo missense variants mapped to the kinase domain of CDK19, including two recurrent changes at residues Tyr32 and Gly28. In vitro autophosphorylation and substrate phosphorylation assays revealed that kinase activity of protein was lower for p.Gly28Arg and higher for p.Tyr32His substitutions compared with that of the wild-type protein. Injection of CDK19 messenger RNA (mRNA) with either the Tyr32His or the Gly28Arg variants using in vivo zebrafish model significantly increased fraction of embryos with morphological abnormalities. Overall, the phenotype of the now 14 individuals with CDK19-related disorder includes universal developmental delay and facial dysmorphism, hypotonia (79%), seizures (64%), ophthalmologic anomalies (64%), and autism/autistic traits (56%).

CONCLUSION

CDK19 de novo missense variants are responsible for a novel neurodevelopmental disorder. Both kinase assay and zebrafish experiments showed that the pathogenetic mechanism may be more diverse than previously thought.

MED12-Related (Neuro)Developmental Disorders: A Question of Causality

MED12 is a member of the Mediator complex that is involved in the regulation of transcription. Missense variants in MED12 cause FG syndrome, Lujan-Fryns syndrome, and Ohdo syndrome, as well as non-syndromic intellectual disability (ID) in hemizygous males. Recently, female patients with de novo missense variants and de novo protein truncating variants in MED12 were described, resulting in a clinical spectrum centered around ID and Hardikar syndrome without ID. The missense variants are found throughout MED12, whether they are inherited in hemizygous males or de novo in females. They can result in syndromic or nonsyndromic ID. The de novo nonsense variants resulting in Hardikar syndrome that is characterized by facial clefting, pigmentary retinopathy, biliary anomalies, and intestinal malrotation, are found more N-terminally, whereas the more C-terminally positioned variants are de novo protein truncating variants that cause a severe, syndromic phenotype consisting of ID, facial dysmorphism, short stature, skeletal abnormalities, feeding difficulties, and variable other abnormalities. This broad range of distinct phenotypes calls for a method to distinguish between pathogenic and non-pathogenic variants in MED12. We propose an isogenic iNeuron model to establish the unique gene expression patterns that are associated with the specific MED12 variants. The discovery of these patterns would help in future diagnostics and determine the causality of the MED12 variants.

A novel variant of CDK19 causes a severe neurodevelopmental disorder with infantile spasms

Infantile spasms are a potentially catastrophic form of epilepsy syndrome that are usually associated with substantial developmental delay and commonly occur in children younger than 1 yr. Recent reports on four cases revealed that variants harbored in a novel gene CDK19 were causative for the syndrome. We report a fifth affected individual, a 10-mo-old male patient who presented with a neurodevelopmental syndrome characterized by infantile spasms. We identified a novel de novo missense variant c.92C > A (p.Thr31Asn) in CDK19 that was classified as a likely pathogenic disease-causing variant. The characterized clinical phenotypes of the proband were similar to the previously reported four patients, but he had few variable features including earlier seizure onset age and earlier occurring developmental abnormality. Protein structure modeling analysis revealed that CDK19 variants may disable its kinase activity, which would further impede the transcriptional regulation, thus leading to detrimental pathologies. Our report expanded CDK19 genotype spectrum and further demonstrated that a CDK19 missense variant was causative of neurodevelopmental disorder clinically marked by infantile spasms.

Potential roles of mediator Complex Subunit 13 in Cardiac Diseases

Mediator complex subunit 13 (MED13, previously known as THRAP1 and TRAP240) is a subunit of the cyclin-dependent kinase 8 (CDK8) kinase module in the eukaryotic mediator complex. MED13 has been known to play critical roles in cell cycle, development, and growth. The purpose of this review is to comprehensively discuss its newly identified potential roles in myocardial energy metabolism and non-metabolic cardiovascular diseases. Evidence indicates that cardiac MED13 mainly participates in the regulation of nuclear receptor signaling, which drives the transcription of genes involved in modulating cardiac and systemic energy homeostasis. MED13 is also associated with several pathological conditions, such as metabolic syndrome and thyroid disease-associated heart failure. Therefore, MED13 constitutes a potential therapeutic target for the regulation of metabolic disorders and other cardiovascular diseases.

Whole-genome sequencing to identify candidate genes for litter size and to uncover the variant function in goats (Capra hircus)

To select candidate genes for goat prolificacy, we managed six multi- and six single-kid female goats at the same feeding level and in the same management mode over a 4-year period. These goats showed stable differences in litter size over five continuous parturition records. Whole-genome re-sequencing was used in all 12 to select candidate genes, namely, AURKA, ENDOG, SOX2, RORA, GJA10, RXFP2, CDC25C, and NANOS3, by the strength of their differentiation signals. Most of the selected genes were enriched in the coiled coil process and ovarian development, which suggests that the coiled coil process has a potential regulatory effect on fecundity. Detection of the distribution of variants and association analyses with litter size in 400 goats showed that NANOS3 exon mutations may lead to a transformation of the protein structure. The variation in CDC25C, ENDOG, and NANOS3 showed a significant association with litter size. These results can contribute to the improvement of reproduction traits in the artificial breeding of goats.

Could the MED13 mutations manifest as a Kabuki-like syndrome?

MED13-related disorder is a new neurodevelopmental disorder recently described in literature, which belongs to the group of CDK8-kinase module genes-associated conditions. It is characterized by variable intellectual disability and/or developmental delays, especially in language. Autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD), eye or vision problems, hypotonia, mild congenital hearth abnormalities and dysmorphisms have been described among individuals with MED13 mutations. We report the case of a 13-year-old girl who received a previous clinical diagnosis of Kabuki syndrome (KS) without mutations in classic KS genes. After a whole exome sequencing (WES) analysis a de novo missense mutation in MED13 (c.C979T; p.Pro327Ser) was found. This variant has been once described in literature as accountable for a novel neurodevelopmental disorder. The aim of this report is to improve clinical delineation of MED13-related condition and to explore differences and similarities between KS spectrum and MED13-related disorders.

Angel or Devil ? - CDK8 as the new drug target

Cyclin-dependent kinase 8 (CDK8) plays an momentous role in transcription regulation by forming kinase module or transcription factor phosphorylation. A large number of evidences have identified CDK8 as an important factor in cancer occurrence and development. In addition, CDK8 also participates in the regulation of cancer cell stress response to radiotherapy and chemotherapy, assists tumor cell invasion, metastasis, and drug resistance. Therefore, CDK8 is regarded as a promising target for cancer therapy. Most studies in recent years supported the role of CDK8 as a carcinogen, however, under certain conditions, CDK8 exists as a tumor suppressor. The functional diversity of CDK8 and its exceptional role in different types of cancer have aroused great interest from scientists but even more controversy during the discovery of CDK8 inhibitors. In addition, CDK8 appears to be an effective target for inflammation diseases and immune system disorders. Therefore, we summarized the research results of CDK8, involving physiological/pathogenic mechanisms and the development status of compounds targeting CDK8, provide a reference for the feasibility evaluation of CDK8 as a therapeutic target, and guidance for researchers who are involved in this field for the first time.

Translational Diagnostics: An In-House Pipeline to Validate Genetic Variants in Children with Undiagnosed and Rare Diseases

Diagnosis is essential for the management and treatment of patients with rare diseases. In a group of patients, the genetic study identifies variants of uncertain significance or inconsistent with the phenotype; therefore, it is urgent to develop novel strategies to reach the definitive diagnosis. Herein, we develop the in-house Translational Diagnostics Program (TDP) to validate genetic variants as part of the diagnostic process with the close collaboration of physicians, clinical scientists, and research scientists. The first 7 of 33 consecutive patients for whom exome-based tests were not diagnostic were investigated. The TDP pipeline includes four steps: (i) phenotype assessment, (ii) literature review and prediction of in silico pathogenicity, (iii) experimental functional studies, and (iv) diagnostic decision-making. Re-evaluation of the phenotype and re-analysis of the exome allowed the diagnosis in one patient. In the remaining patients, the studies included either cDNA cloning or PCR-amplified genomic DNA, or the use of patients' fibroblasts. A comparative computational analysis of confocal microscopy images and studies related to the protein function was performed. In five of these six patients, evidence of pathogenicity of the genetic variant was found, which was validated by physicians. The current research demonstrates the feasibility of the TDP to support and resolve intramural medical problems when the clinical significance of the patient variant is unknown or inconsistent with the phenotype.

Pathogenesis of CDK8-associated disorder: two patients with novel CDK8 variants and in vitro and in vivo functional analyses of the variants

Cyclin-dependent kinase 8 (CDK8) is a member of the CDK/Cyclin module of the mediator complex. A recent study reported that heterozygous missense CDK8 mutations cause a neurodevelopmental disorder in humans. The mechanistic basis of CDK8-related disorder has yet to be delineated. Here, we report 2 patients with de novo missense mutations within the kinase domain of CDK8 along with the results of in vitro and in vivo functional analyses using a zebrafish model. Patient 1 and Patient 2 had intellectual disabilities and congenital anomalies. Exome analyses showed that patient 1 had a heterozygous de novo missense p.G28A variant in the CDK8 (NM_001260.3) gene and patient 2 had a heterozygous de novo missense p.N156S variant in the CDK8 gene. We assessed the pathogenicity of these two variants using cultured-cells and zebrafish model. An in vitro kinase assay of human CDK8 showed that enzymes with a p.G28A or p.N156S substitution showed decreased kinase activity. An in vivo assays of zebrafish overexpression analyses also showed that the p.G28A and p.N156S alleles were hypomorphic alleles. Importantly, the inhibition of CDK8 kinase activity in zebrafish embryos using a specific chemical inhibitor induced craniofacial and heart defects similar to the patients' phenotype. Taken together, zebrafish studies showed that non-synonymous variants in the kinase domain of CDK8 act as hypomorphic alleles causing human congenital disorder.

The extent of cyclin C promoter occupancy directs changes in stress-dependent transcription

The Cdk8 kinase module (CKM) is a detachable Mediator subunit composed of cyclin C and one each of paralogs Cdk8/Cdk19, Med12/Med12L, and Med13/Med13L. Our previous RNA-Seq studies demonstrated that cyclin C represses a subset of hydrogen peroxide-induced genes under normal conditions but is involved in activating other loci following stress. Here, we show that cyclin C directs this transcriptional reprograming through changes in its promoter occupancy. Following peroxide stress, cyclin C promoter occupancy increased for genes it activates while decreasing at loci it represses under normal conditions. Promoter occupancy of other CKM components generally mirrored cyclin C, indicating that the CKM moves as a single unit. It has previously been shown that some cyclin C leaves the nucleus following cytotoxic stress to induce mitochondrial fragmentation and apoptosis. We observed that CKM integrity appeared compromised at a subset of repressed promoters, suggesting a source of cyclin C that is targeted for nuclear release. Interestingly, mTOR inhibition induced a new pattern of cyclin C promoter occupancy indicating that this control is fine-tuned to the individual stress. Using inhibitors, we found that Cdk8 kinase activity is not required for CKM movement or repression but was necessary for full gene activation. In conclusion, this study revealed that different stress stimuli elicit specific changes in CKM promoter occupancy correlating to altered transcriptional outputs. Finally, although CKM components were recruited or expelled from promoters as a unit, heterogeneity was observed at individual promoters, suggesting a mechanism to generate gene- and stress-specific responses.

Mediator Roles Going Beyond Transcription

Dysfunctions of nuclear processes including transcription and DNA repair lead to severe human diseases. Gaining an understanding of how these processes operate in the crowded context of chromatin can be particularly challenging. Mediator is a large multiprotein complex conserved in eukaryotes with a key coactivator role in the regulation of RNA polymerase (Pol) II transcription. Despite intensive studies, the molecular mechanisms underlying Mediator function remain to be fully understood. Novel findings have provided insights into the relationship between Mediator and chromatin architecture, revealed its role in connecting transcription with DNA repair and proposed an emerging mechanism of phase separation involving Mediator condensates. Recent developments in the field suggest multiple functions of Mediator going beyond transcriptional processes per se that would explain its involvement in various human pathologies.

Cyclin-dependent kinases and rare developmental disorders

Extensive studies in the past 30 years have established that cyclin-dependent kinases (CDKs) exert many diverse, important functions in a number of molecular and cellular processes that are at play during development. Not surprisingly, mutations affecting CDKs or their activating cyclin subunits have been involved in a variety of rare human developmental disorders. These recent findings are reviewed herein, giving a particular attention to the discovered mutations and their demonstrated or hypothesized functional consequences, which can account for pathological human phenotypes. The review highlights novel, important CDK or cyclin functions that were unveiled by their association with human disorders, and it discusses the shortcomings of mouse models to reveal some of these functions. It explains how human genetics can be used in combination with proteome-scale interaction databases to loom regulatory networks around CDKs and cyclins. Finally, it advocates the use of these networks to profile pathogenic CDK or cyclin variants, in order to gain knowledge on protein function and on pathogenic mechanisms.

De Novo Variants in CDK19 Are Associated with a Syndrome Involving Intellectual Disability and Epileptic Encephalopathy

We identified three unrelated individuals with de novo missense variants in CDK19, encoding a cyclin-dependent kinase protein family member that predominantly regulates gene transcription. These individuals presented with hypotonia, global developmental delay, epileptic encephalopathy, and dysmorphic features. CDK19 is conserved between vertebrate and invertebrate model organisms, but currently abnormalities in CDK19 are not known to be associated with a human disorder. Loss of Cdk8, the fly homolog of CDK19, causes larval lethality, which is suppressed by expression of human CDK19 reference cDNA. In contrast, the CDK19 p.Tyr32His and p.Thr196Ala variants identified in the affected individuals fail to rescue the loss of Cdk8 and behave as null alleles. Additionally, neuronal RNAi-mediated knockdown of Cdk8 in flies results in semi-lethality. The few eclosing flies exhibit severe seizures and a reduced lifespan. Both phenotypes are fully suppressed by moderate expression of the CDK19 reference cDNA but not by expression of the two variants. Finally, loss of Cdk8 causes an obvious loss of boutons and synapses at larval neuromuscular junctions (NMJs). Together, our findings demonstrate that human CDK19 fully replaces the function of Cdk8 in the fly, the human disease-associated CDK19 variants behave as strong loss-of-function variants, and deleterious CDK19 variants underlie a syndromic neurodevelopmental disorder.

Genetic analysis in patients with newly diagnosed glioblastomas treated with interferon-beta plus temozolomide in comparison with temozolomide alone

PURPOSE

This study aimed to explore the genetic alterations and to identify good responders in the experimental arm in the tumor samples from newly diagnosed glioblastoma (GBM) patients enrolled in JCOG0911; a randomized phase II trial was conducted to compare the efficacy of interferonβ (IFNβ) plus temozolomide (TMZ) with that of TMZ alone.

EXPERIMENTAL

DESIGN: Of 122 tumors, we performed deep targeted sequencing to determine the somatic mutations, copy number variations, and tumor mutation burden; pyrosequencing for O⁶-methylguanine-DNA methyltransferase (MGMT) promoter methylation; Sanger sequencing for the telomerase reverse transcriptase (TERT) promoter; and microsatellite instability (MSI) testing in 95, 91, 91 and 72 tumors, respectively. We performed a multivariable Cox regression analysis using backward stepwise selection of variables including clinical factors (sex, age, performance status, residual tumor after resection, tumor location) and genetic alterations.

RESULTS

Deep sequencing detected an IDH1 mutation in 13 tumors (14%). The MGMT promoter methylation by quantitative pyrosequencing was observed in 41% of the tumors. A mutation in the TERT promoter was observed in 69% of the tumors. While high tumor mutation burden (> 10 mutations per megabase) was seen in four tumors, none of the tumors displayed MSI-high. The clinical and genetic factors considered as independent favorable prognostic factors were gross total resection (hazard ratio [HR]: 0.49, 95% confidence interval, 0.30-0.81, P = 0.0049) and MGMT promoter methylation (HR: 0.43, 0.21-0.88, P = 0.023). However, tumor location at the temporal lobe (HR: 1.90, 1.22-2.95, P = 0.0046) was an independent unfavorable prognostic factor. No predictive factors specific to the TMZ + IFNβ + Radiotherapy (RT) group were found.

CONCLUSION

This additional sub-analytical study of JCOG0911 among patients with newly diagnosed GBM showed that tumor location at the temporal lobe, gross total resection, and MGMT promoter methylation were significant prognostic factors, although no factors specific to IFNβ addition were identified.

Exome sequencing for perinatal phenotypes: The significance of deep phenotyping

OBJECTIVE

To ascertain the performance of exome sequencing (ES) technology for determining the etiological basis of abnormal perinatal phenotypes and to study the impact of comprehensive phenotyping on variant prioritization.

METHODS

A carefully selected cohort of 32/204 fetuses with abnormal perinatal phenotypes following postmortem/postnatal deep phenotyping underwent ES to identify a causative variant for the fetal phenotype. A retrospective comparative analysis of the prenatal versus postmortem/postnatal phenotype-based variant prioritization was performed with aid of Phenolyzer software. A review of selected literature reports was done to examine the completeness of phenotypic information for cases in those reports and how it impacted the performance of fetal ES.

RESULTS

In 18/32 (56%) fetuses, a pathogenic/likely pathogenic variant was identified. This included novel genotype-phenotype associations, expanded prenatal phenotypes of known Mendelian disorders and dual Mendelian diagnoses. The retrospective analysis revealed that the putative diagnostic variant could not be identified on basis of prenatal findings alone in 15/22 (68%) cases, indicating the importance of comprehensive postmortem/postnatal phenotype information. Literature review was supportive of these findings but could not be conclusive due to marked heterogeneity of involved studies.

CONCLUSION

Comprehensive phenotyping is essential for improving diagnostic performance and facilitating identification of novel genotype-phenotype associations in perinatal cohorts undergoing ES.

Decoding the PTM-switchboard of Notch

The developmentally indispensable Notch pathway exhibits a high grade of pleiotropism in its biological output. Emerging evidence supports the notion of post-translational modifications (PTMs) as a modus operandi controlling dynamic fine-tuning of Notch activity. Although, the intricacy of Notch post-translational regulation, as well as how these modifications lead to multiples of divergent Notch phenotypes is still largely unknown, numerous studies show a correlation between the site of modification and the output. These include glycosylation of the extracellular domain of Notch modulating ligand binding, and phosphorylation of the PEST domain controlling half-life of the intracellular domain of Notch. Furthermore, several reports show that multiple PTMs can act in concert, or compete for the same sites to drive opposite outputs. However, further investigation of the complex PTM crosstalk is required for a complete understanding of the PTM-mediated Notch switchboard. In this review, we aim to provide a consistent and up-to-date summary of the currently known PTMs acting on the Notch signaling pathway, their functions in different contexts, as well as explore their implications in physiology and disease. Furthermore, we give an overview of the present state of PTM research methodology, and allude to a future with PTM-targeted Notch therapeutics.