Clinical findings from the landmark MEF2C-related disorders natural history study

Investigating pain-related medication use and contribution to polypharmacy in adults with intellectual disabilities: a systematic review

BACKGROUND

Adults with intellectual disability experience more pain than adults without and, despite a higher number of medications being prescribed, may be less likely to receive medication for pain. We conducted a systematic review of existing literature on medication for pain and painful conditions in adults with intellectual disability to explore if there is any association with polypharmacy, multimorbidity or demographic characteristics.

METHODS

This systematic review followed PRISMA guidelines. Medline, Embase, PubMed, PsycINFO, Web of Science, CINAHL, Cochrane Library and Scopus were searched from January 2000 to 21st October 2024. We included original, peer-reviewed observational, qualitative or mixed-method studies published in English with data on medication for pain or painful conditions in adults with intellectual disability. Two independent reviewers performed study selection, data extraction, and quality assessment; disagreements were resolved by a third reviewer. Adapted Newcastle-Ottawa Scale or the Critical Appraisal Skills Programme for qualitative studies was used for quality assessment of included studies and findings were reported via narrative synthesis. PROSPERO registration: CRD42023415051.

RESULTS

Twenty-seven of 26,170 articles met the eligibility criteria. Adults with intellectual disability were more likely to have simple analgesic medication than non-steroidal anti-inflammatory drugs, opioids or adjuvant pain medications than the general population. Psychotropic medications were more commonly prescribed in adults with intellectual disability than medication for pain or painful conditions. Adults with intellectual disability and caregivers reported under-recognition and most likely under-treatment of pain.

CONCLUSIONS

Adults with intellectual disability may receive less pharmacological management of pain with analgesics and medication for painful conditions despite the high prevalence of polypharmacy, suggesting pain is under-treated. Better assessment and pharmacological treatment of pain and painful conditions is a key future research priority to address this health inequality and improve quality of life for this vulnerable group of people.

Developmental Disruption of Mef2c in Medial Ganglionic Eminence-Derived Cortical Inhibitory Interneurons Impairs Cellular and Circuit Function

BACKGROUND

MEF2C is strongly linked to various neurodevelopmental disorders including autism, intellectual disability, schizophrenia, and attention-deficit/hyperactivity disorder. Mice that constitutively lack 1 copy of Mef2c or selectively lack both copies of Mef2c in cortical excitatory neurons display a variety of behavioral phenotypes associated with neurodevelopmental disorders. The MEF2C protein is a transcription factor necessary for cellular development and synaptic modulation of excitatory neurons. MEF2C is also expressed in a subset of cortical GABAergic (gamma-aminobutyric acidergic) inhibitory neurons, but its function in those cell types remains largely unknown.

METHODS

Using conditional deletions of the Mef2c gene in mice, we investigated the role of MEF2C in parvalbumin-expressing interneurons (PV-INs), the largest subpopulation of cortical GABAergic cells, at 2 developmental time points. We performed slice electrophysiology, in vivo recordings, and behavior assays to test how embryonic and late postnatal loss of MEF2C from GABAergic INs impacts their survival and maturation and alters brain function and behavior.

RESULTS

Loss of MEF2C from PV-INs during embryonic, but not late postnatal, development resulted in reduced PV-IN number and failure of PV-INs to molecularly and synaptically mature. In association with these deficits, early loss of MEF2C in GABAergic INs led to abnormal cortical network activity, hyperactive and stereotypic behavior, and impaired cognitive and social behavior.

CONCLUSIONS

MEF2C expression is critical for the development of cortical GABAergic INs, particularly PV-INs. Embryonic loss of function of MEF2C mediates dysfunction of GABAergic INs, leading to altered in vivo patterns of cortical activity and behavioral phenotypes associated with neurodevelopmental disorders.

The function of Mef2c toward the development of excitatory and inhibitory cortical neurons

Neurodevelopmental disorders (NDDs) are caused by abnormal brain development, leading to altered brain function and affecting cognition, learning, self-control, memory, and emotion. NDDs are often demarcated as discrete entities for diagnosis, but empirical evidence indicates that NDDs share a great deal of overlap, including genetics, core symptoms, and biomarkers. Many NDDs also share a primary sensitive period for disease, specifically the last trimester of pregnancy in humans, which corresponds to the neonatal period in mice. This period is notable for cortical circuit assembly, suggesting that deficits in the establishment of brain connectivity are likely a leading cause of brain dysfunction across different NDDs. Regulators of gene programs that underlie neurodevelopment represent a point of convergence for NDDs. Here, we review how the transcription factor MEF2C, a risk factor for various NDDs, impacts cortical development. Cortical activity requires a precise balance of various types of excitatory and inhibitory neuron types. We use MEF2C loss-of-function as a study case to illustrate how brain dysfunction and altered behavior may derive from the dysfunction of specific cortical circuits at specific developmental times.

Exploring penetrance of clinically relevant variants in over 800,000 humans from the Genome Aggregation Database

Incomplete penetrance, or absence of disease phenotype in an individual with a disease-associated variant, is a major challenge in variant interpretation. Studying individuals with apparent incomplete penetrance can shed light on underlying drivers of altered phenotype penetrance. Here, we investigate clinically relevant variants from ClinVar in 807,162 individuals from the Genome Aggregation Database (gnomAD), demonstrating improved representation in gnomAD version 4. We then conduct a comprehensive case-by-case assessment of 734 predicted loss of function variants (pLoF) in 77 genes associated with severe, early-onset, highly penetrant haploinsufficient disease. We identified explanations for the presumed lack of disease manifestation in 701 of the variants (95%). Individuals with unexplained lack of disease manifestation in this set of disorders rarely occur, underscoring the need and power of deep case-by-case assessment presented here to minimize false assignments of disease risk, particularly in unaffected individuals with higher rates of secondary properties that result in rescue.

Developmental disruption of Mef2c in Medial Ganglionic Eminence-derived cortical inhibitory interneurons impairs cellular and circuit function

MEF2C is strongly linked to various neurodevelopmental disorders (NDDs) including autism, intellectual disability, schizophrenia, and attention-deficit/hyperactivity. Mice constitutively lacking one copy of Mef2c , or selectively lacking both copies of Mef2c in cortical excitatory neurons, display a variety of behavioral phenotypes associated with NDDs. The MEF2C protein is a transcription factor necessary for cellular development and synaptic modulation of excitatory neurons. MEF2C is also expressed in a subset of cortical GABAergic inhibitory neurons, but its function in those cell types remains largely unknown. Using conditional deletions of the Mef2c gene in mice, we investigated the role of MEF2C in Parvalbumin-expressing Interneurons (PV-INs), the largest subpopulation of cortical GABAergic cells, at two developmental timepoints. We performed slice electrophysiology, in vivo recordings, and behavior assays to test how embryonic and late postnatal loss of MEF2C from GABAergic interneurons impacts their survival and maturation, and alters brain function and behavior. We found that loss of MEF2C from PV-INs during embryonic, but not late postnatal, development resulted in reduced PV-IN number and failure of PV-INs to molecularly and synaptically mature. In association with these deficits, early loss of MEF2C in GABAergic interneurons lead to abnormal cortical network activity, hyperactive and stereotypic behavior, and impaired cognitive and social behavior. Our findings indicate that MEF2C expression is critical for the development of cortical GABAergic interneurons, particularly PV-INs. Embryonic loss of function of MEF2C mediates dysfunction of GABAergic interneurons, leading to altered in vivo patterns of cortical activity and behavioral phenotypes associated with neurodevelopmental disorders.

MEF2C Hypofunction in GABAergic Cells Alters Sociability and Prefrontal Cortex Inhibitory Synaptic Transmission in a Sex-Dependent Manner

Background

Heterozygous mutations or deletions of MEF2C cause a neurodevelopmental disorder termed MEF2C haploinsufficiency syndrome (MCHS), characterized by autism spectrum disorder and neurological symptoms. In mice, global Mef2c heterozygosity has produced multiple MCHS-like phenotypes. MEF2C is highly expressed in multiple cell types of the developing brain, including GABAergic (gamma-aminobutyric acidergic) inhibitory neurons, but the influence of MEF2C hypofunction in GABAergic neurons on MCHS-like phenotypes remains unclear.

Methods

We employed GABAergic cell type-specific manipulations to study mouse Mef2c heterozygosity in a battery of MCHS-like behaviors. We also performed electroencephalography, single-cell transcriptomics, and patch-clamp electrophysiology and optogenetics to assess the impact of Mef2c haploinsufficiency on gene expression and prefrontal cortex microcircuits.

Results

Mef2c heterozygosity in developing GABAergic cells produced female-specific deficits in social preference and altered approach-avoidance behavior. In female, but not male, mice, we observed that Mef2c heterozygosity in developing GABAergic cells produced 1) differentially expressed genes in multiple cell types, including parvalbumin-expressing GABAergic neurons, 2) baseline and social-related frontocortical network activity alterations, and 3) reductions in parvalbumin cell intrinsic excitability and inhibitory synaptic transmission onto deep-layer pyramidal neurons.

Conclusions

MEF2C hypofunction in female, but not male, developing GABAergic cells is important for typical sociability and approach-avoidance behaviors and normal parvalbumin inhibitory neuron function in the prefrontal cortex of mice. While there is no apparent sex bias in autism spectrum disorder symptoms of MCHS, our findings suggest that GABAergic cell-specific dysfunction in females with MCHS may contribute disproportionately to sociability symptoms.

Integrative miRNA-mRNA profiling of human epidermis: unique signature of SCN9A painful neuropathy

Personalized management of neuropathic pain is an unmet clinical need due to heterogeneity of the underlying aetiologies, incompletely understood pathophysiological mechanisms and limited efficacy of existing treatments. Recent studies on microRNA in pain preclinical models have begun to yield insights into pain-related mechanisms, identifying nociception-related species differences and pinpointing potential drug candidates. With the aim of bridging the translational gap towards the clinic, we generated a human pain-related integrative miRNA and mRNA molecular profile of the epidermis, the tissue hosting small nerve fibres, in a deeply phenotyped cohort of patients with sodium channel-related painful neuropathy not responding to currently available therapies. We identified four miRNAs strongly discriminating patients from healthy individuals, confirming their effect on differentially expressed gene targets driving peripheral sensory transduction, transmission, modulation and post-transcriptional modifications, with strong effects on gene targets including NEDD4. We identified a complex epidermal miRNA-mRNA network based on tissue-specific experimental data suggesting a cross-talk between epidermal cells and axons in neuropathy pain. Using immunofluorescence assay and confocal microscopy, we observed that Nav1.7 signal intensity in keratinocytes strongly inversely correlated with NEDD4 expression that was downregulated by miR-30 family, suggesting post-transcriptional fine tuning of pain-related protein expression. Our targeted molecular profiling advances the understanding of specific neuropathic pain fine signatures and may accelerate process towards personalized medicine in patients with neuropathic pain.