👤 Ellen Lockhart

Impaired glymphatic function is considered an important characteristic of cognitive decline, but the role of tau pathology as a mediator remains unclear. This study investigated whether tau burden mediates the association between diffusion tensor image analysis along the perivascular space (DTI-ALPS) and cognitive impairment or brain atrophy. Also, we explored whether DTI-ALPS index predicts longitudinal cognitive deterioration over time. We included 144 individuals with mild cognitive impairment (MCI), Alzheimer's disease dementia (ADD), and other dementia, or normal cognition. All participants underwent 3.0-Tesla MRI, DTI-ALPS index was significantly lower in cognitively impaired individuals compared to cognitively normal (CN) participants. Lower DTI-ALPS index was associated with higher tau burden and worse cognitive function. Tau burden was also inversely associated with cognition. Mediation analysis indicated that tau burden accounted for approximately 21-27% of the association between DTI-ALPS and cognition. Longitudinal analysis showed baseline lower DTI-ALPS index also predicted faster longitudinal cognitive decline. Our findings suggest that the DTI-ALPS index is an indirect marker of glymphatic dysfunction associated with tau accumulation and cognitive decline. Tau pathology may partially link compromised glymphatic clearance to cognitive impairment. Show less

Periventricular nodular heterotopia (PVNH) is a common malformation of cortical development. We describe a distinctive imaging phenotype characterized by bilateral small heterotopic nodules of grey matter in the frontal periventricular regions, with an overview of the clinical, imaging, and genetic features. Investigators reviewed available brain MRI studies, clinical records and genetic findings of 32 individuals with bilateral frontal PVNH, ascertained from multiple centres between 1996 and 2021. The imaging phenotype consists of multiple, small, bilateral nodules of PVNH maximal along the frontal horns of the lateral ventricles. Frontal PVNH was associated with heterogeneous, often subtle, additional brain malformations in 72 % (23/32) individuals. The clinical phenotype was variable and included mild focal epilepsy in 7/32 and mild-moderate cognitive impairment or developmental delay in 13/32. Microarray was normal in 13/16 and exome or genome sequencing normal in 8/13 where testing was performed. A genetic diagnosis was achieved in seven patients; pathogenic chromosome deletions of 7q11.23 and 7p22.1, pathogenic intragenic variants in KANSL1, STXBP1 and MAP1B (mother-daughter pair), and a combined 13q12.12 deletion (containing SACS) and an intragenic SACS variant. Bilateral frontal PVNH has a variable clinical phenotype, but generally milder sequelae than other forms of bilateral PVNH. A genetic diagnosis was made by chromosome microarray alone in 13 % or by exome or genome sequencing in 38 % where access to testing was available, with no recurrent genetic cause being found. Our PVNH cohort data suggest that PVNH could be classified in three main groups: FLNA-associated "classic" bilateral frontocentral PVNH, posterior/infrasylvian PVNH and this third pattern of bilateral frontal PVNH, accounting for ∼10 % of all cases of PVNH. Show less

Clinical case-based studies have identified rare pathogenic variants in several genes as causes of severe early-onset obesity, but their penetrance and interaction with polygenic susceptibility in the general population remain unclear. We analyzed the United Kingdom Biobank (UKBB) whole-exome sequence data to assess the effects of heterozygous variants in 9 previously reported genes on adult body mass index (BMI) and recalled childhood adiposity. Among 419 581 UKBB participants, we identified heterozygous carriers of coding variants that were (1) experimentally characterized as loss of function (LoF), or (2) bioinformatically predicted as rare (minor allele frequency <0.1%) LoF. We assessed variant-level and gene-level population penetrance of obesity and associations with adult BMI and recalled childhood adiposity, and tested the statistical interaction between rare variant carriage and a BMI polygenic score. Considering experimentally characterized LoF variants (excluding MC4R), we identified 22 heterozygous and 2 homozygous variants in 3 autosomal recessive genes (POMC, PCSK1, LEPR), and 3 autosomal dominant genes (SH2B1, SIM1, KSR2) with at least 10 carriers in the UKBB. Obesity penetrance among carriers ranged from 8% to 29% (median 23%), and none was significantly different from noncarriers (24%, all P > .05). For bioinformatically predicted rare LoF variants, gene-based burden tests showed that carriage of heterozygous variants in MC4R, PCSK1, and POMC was associated with higher adult BMI (effect sizes ranged from 0.5 to 2.5 kg/m2, all P < .003), with no significant interaction effects with common variant polygenic risk of BMI. This study provides the population-specific report of variant penetrance of known obesity genes and confirmed the heterozygous rare variant effects in MC4R, POMC, and PCSK1. We also underscore the utility of population-based studies in supporting variant classifications. Show less

Infantile epileptic spasms syndrome is a severe epilepsy of infancy that is often associated with focal malformations of cortical development. This study aimed to elucidate the genetic landscape and histopathologic aetiologies of infantile epileptic spasms syndrome due to focal malformations of cortical development requiring surgery. Fifty-nine children with a history of infantile epileptic spasms syndrome and focal malformations of cortical development on MRI were studied. Genetic testing of resected brain tissue was performed by high-coverage targeted panel sequencing or exome sequencing. Histopathology and MRI were reviewed, and integrated clinico-pathological diagnoses were established. A genetic diagnosis was achieved in 47 children (80% of cohort). Germline pathogenic variants were identified in 27/59 (46%) children, in Show less

Pathogenic variants in PI3K-AKT-mTOR pathway and GATOR1 complex genes resulting in hyperactivation of mechanistic target of rapamycin (mTOR) complex 1 are a major cause of drug-resistant epilepsy and focal cortical malformations (FCM). Resective neurosurgery is often required to achieve seizure control in patients with mTORopathies due to lack of effectiveness of nonsurgical therapies, including antiseizure medication and mTOR inhibitors. Elevated hyperpolarization-activated cyclic nucleotide-gated potassium channel isoform 4 (HCN4) has been proposed as a key marker in some mTOR-related brain malformations. This study aimed to investigate HCN4 as a biomarker in the brain across the genetic spectrum of mTORopathies in humans. Our study investigated the relative steady-state levels and cellular localization of HCN4 in resected human brain tissue from 18 individuals with mTORopathies (3 individuals with tuberous sclerosis complex (TSC) due to Elevated HCN4 was observed to be highly restricted to abnormal cell types (dysmorphic neurons and balloon cells) in brain tissue from all mTORopathy tissues ( HCN4 provides a biomarker for the genetic spectrum of mTORopathies and may present a potential therapeutic target for seizure control in mTOR-related epilepsy. Show less

Type 2 diabetes (T2D) is a heritable metabolic disorder. While population studies have identified hundreds of common genetic variants associated with T2D, the role of rare (frequency < 0.1%) protein-coding variation is less clear. We performed exome sequence analysis in 418,436 (n = 32,374 T2D cases) individuals in the UK Biobank. We identified previously reported genes ( Show less

Multiple gene defects cause Batten disease. Accelerated apoptosis accounts for neurodegeneration in the late infantile and juvenile forms that are due to defects in the CLN3 and CLN2 genes. Extensive neuronal death is seen in CLN2- and CLN3-deficient human brain as well as in CLN6-deficient sheep brain and retina. When neurons in late infantile and juvenile brain survive, they manage to do so by upregulating the neuroprotective molecule Bcl-2. The CLN3 gene has antiapoptotic properties at the molecular level. We show that the CLN2 gene is neuroprotective: it enhances growth of NT2 cells and maintains survival of human postmitotic hNT neurons. Conversely, blocking CLN3 or CLN2 expression in hNT neurons with adenoviral antisense-CLN3 or antisense-CLN2-AAV2 constructs causes apoptosis. The drug flupirtine is a triaminopyridine derivative that acts as a nonopioid analgesic. Flupirtine upregulates Bcl-2, increases glutathione levels, activates an inwardly rectifying potassium channel, and delays loss of intermitochondrial membrane calcium retention capacity. We show that flupirtine aborts etoposide-induced apoptosis in CLN1-, CLN2-, CLN3-, and CLN6-deficient as well as normal lymphoblasts. Flupirtine also prevents the death of CLN3- and CLN2-deficient postmitotic hNT neurons at the mitochondrial level. We show that a mechanism of neuroprotection exerted by flupirtine involves complete functional antagonism of N-methyl-D-aspartate or N-methyl-D-aspartate-induced neuronal apoptosis. Flupirtine may be useful as a drug capable of halting the progression of neurodegenerative diseases caused by dysregulated apoptosis. Show less