The clinical, imaging, pathological and genetic landscape of bottom-of-sulcus dysplasia.

Bottom-of-sulcus dysplasia (BOSD) is increasingly recognized as a cause of drug-resistant, surgically-remediable, focal epilepsy, often in seemingly MRI-negative patients. We describe the clinical manifestations, morphological features, localization patterns and genetics of BOSD, with the aims of improving management and understanding pathogenesis. We studied 85 patients with BOSD diagnosed between 2005-2022. Presenting seizure and EEG characteristics, clinical course, genetic findings and treatment response were obtained from medical records. MRI (3 T) and 18F-FDG-PET scans were reviewed systematically for BOSD morphology and metabolism. Histopathological analysis and tissue genetic testing were performed in 64 operated patients. BOSD locations were transposed to common imaging space to study anatomical location, functional network localization and relationship to normal MTOR gene expression. All patients presented with stereotyped focal seizures with rapidly escalating frequency, prompting hospitalization in 48%. Despite 42% patients having seizure remissions, usually with sodium channel blocking medications, most eventually became drug-resistant and underwent surgery (86% seizure-free). Prior developmental delay was uncommon but intellectual, language and executive dysfunction were present in 24%, 48% and 29% when assessed preoperatively, low intellect being associated with greater epilepsy duration. BOSDs were missed on initial MRI in 68%, being ultimately recognized following repeat MRI, 18F-FDG-PET or image postprocessing. MRI features were grey-white junction blurring (100%), cortical thickening (91%), transmantle band (62%), increased cortical T1 signal (46%) and increased subcortical FLAIR signal (26%). BOSD hypometabolism was present on 18F-FDG-PET in 99%. Additional areas of cortical malformation or grey matter heterotopia were present in eight patients. BOSDs predominated in frontal and pericentral cortex and related functional networks, mostly sparing temporal and occipital cortex, and limbic and visual networks. Genetic testing yielded pathogenic mTOR pathway variants in 63% patients, including somatic MTOR variants in 47% operated patients and germline DEPDC5 or NPRL3 variants in 73% patients with familial focal epilepsy. BOSDs tended to occur in regions where the healthy brain normally shows lower MTOR expression, suggesting these regions may be more vulnerable to upregulation of MTOR activity. Consistent with the existing literature, these results highlight (i) clinical features raising suspicion of BOSD; (ii) the role of somatic and germline mTOR pathway variants in patients with sporadic and familial focal epilepsy associated with BOSD; and (iii) the role of 18F-FDG-PET alongside high-field MRI in detecting subtle BOSD. The anatomical and functional distribution of BOSDs likely explain their seizure, EEG and cognitive manifestations and may relate to relative MTOR expression.

Aicardi Syndrome Is a Genetically Heterogeneous Disorder.

Aicardi Syndrome (AIC) is a rare neurodevelopmental disorder recognized by the classical triad of agenesis of the corpus callosum, chorioretinal lacunae and infantile epileptic spasms syndrome. The diagnostic criteria of AIC were revised in 2005 to include additional phenotypes that are frequently observed in this patient group. AIC has been traditionally considered as X-linked and male lethal because it almost exclusively affects females. Despite numerous genetic and genomic investigations on AIC, a unifying X-linked cause has not been identified. Here, we performed exome and genome sequencing of 10 females with AIC or suspected AIC based on current criteria. We identified a unique de novo variant, each in different genes: KMT2B, SLF1, SMARCB1, SZT2 and WNT8B, in five of these females. Notably, genomic analyses of coding and non-coding single nucleotide variants, short tandem repeats and structural variation highlighted a distinct lack of X-linked candidate genes. We assessed the likely pathogenicity of our candidate autosomal variants using the TOPflash assay for WNT8B and morpholino knockdown in zebrafish (Danio rerio) embryos for other candidates. We show expression of Wnt8b and Slf1 are restricted to clinically relevant cortical tissues during mouse development. Our findings suggest that AIC is genetically heterogeneous with implicated genes converging on molecular pathways central to cortical development.

A cryptic pathogenic NDUFV1 variant identified by RNA-seq in a patient with normal complex I activity in muscle and transient magnetic resonance imaging changes.

Mitochondrial respiratory chain disorders (MRC) are amongst the most common group of inborn errors of metabolism. MRC, of which complex I deficiency accounts for approximately a quarter, are very diverse, causing a wide range of clinical problems and can be difficult to diagnose. We report an illustrative MRC case whose diagnosis was elusive. Clinical signs included failure to thrive caused by recurrent vomiting, hypotonia and progressive loss of motor milestones. Initial brain imaging suggested Leigh syndrome but without expected diffusion restriction. Muscle respiratory chain enzymology was unremarkable. Whole-genome sequencing identified a maternally inherited NDUFV1 missense variant [NM_007103.4 (NDUFV1):c.1157G > A; p.(Arg386His)] and a paternally inherited synonymous variant [NM_007103.4 (NDUFV1):c.1080G > A; (p.Ser360=)]. RNA sequencing demonstrated aberrant splicing. This case emphasizes the diagnostic odyssey of a patient in whom a confirmed diagnosis was elusive because of atypical features and normal muscle respiratory chain enzyme (RCE) activities, along with a synonymous variant, which are often filtered out from genomic analyses. It also illustrates the following points: (1) complete resolution of magnetic resonance imaging changes may be part of the picture in mitochondrial disease; (2) analysis for synonymous variants is important for undiagnosed patients; and (3) RNA-seq is a powerful tool to demonstrate pathogenicity of putative splicing variants.

WWOX developmental and epileptic encephalopathy: Understanding the epileptology and the mortality risk.

OBJECTIVE: WWOX is an autosomal recessive cause of early infantile developmental and epileptic encephalopathy (WWOX-DEE), also known as WOREE (WWOX-related epileptic encephalopathy). We analyzed the epileptology and imaging features of WWOX-DEE, and investigated genotype-phenotype correlations, particularly with regard to survival. METHODS: We studied 13 patients from 12 families with WWOX-DEE. Information regarding seizure semiology, comorbidities, facial dysmorphisms, and disease outcome were collected. Electroencephalographic (EEG) and brain magnetic resonance imaging (MRI) data were analyzed. Pathogenic WWOX variants from our cohort and the literature were coded as either null or missense, allowing individuals to be classified into one of three genotype classes: (1) null/null, (2) null/missense, (3) missense/missense. Differences in survival outcome were estimated using the Kaplan-Meier method. RESULTS: All patients experienced multiple seizure types (median onset = 5 weeks, range = 1 day-10 months), the most frequent being focal (85%), epileptic spasms (77%), and tonic seizures (69%). Ictal EEG recordings in six of 13 patients showed tonic (n = 5), myoclonic (n = 2), epileptic spasms (n = 2), focal (n = 1), and migrating focal (n = 1) seizures. Interictal EEGs demonstrated slow background activity with multifocal discharges, predominantly over frontal or temporo-occipital regions. Eleven of 13 patients had a movement disorder, most frequently dystonia. Brain MRIs revealed severe frontotemporal, hippocampal, and optic atrophy, thin corpus callosum, and white matter signal abnormalities. Pathogenic variants were located throughout WWOX and comprised both missense and null changes including five copy number variants (four deletions, one duplication). Survival analyses showed that patients with two null variants are at higher mortality risk (p-value = .0085, log-rank test). SIGNIFICANCE: Biallelic WWOX pathogenic variants cause an early infantile developmental and epileptic encephalopathy syndrome. The most common seizure types are focal seizures and epileptic spasms. Mortality risk is associated with mutation type; patients with biallelic null WWOX pathogenic variants have significantly lower survival probability compared to those carrying at least one presumed hypomorphic missense pathogenic variant.

Infantile-onset myoclonic developmental and epileptic encephalopathy: A new RARS2 phenotype.

Recessive variants in RARS2, a nuclear gene encoding a mitochondrial protein, were initially reported in pontocerebellar hypoplasia. Subsequently, a recessive RARS2 early-infantile (<12 weeks) developmental and epileptic encephalopathy was described with hypoglycaemia and lactic acidosis. Here, we describe two unrelated patients with a novel RARS2 phenotype and reanalyse the published RARS2 epilepsy phenotypes and variants. Our novel cases had infantile-onset myoclonic developmental and epileptic encephalopathy, presenting with a progressive movement disorder from 9 months on a background of normal development. Development plateaued and regressed thereafter, with mild to profound impairment. Multiple drug-resistant generalized and focal seizures occurred with episodes of non-convulsive status epilepticus. Seizure types included absence, atonic, myoclonic, and focal seizures. Electroencephalograms showed diffuse slowing, multifocal, and generalised spike-wave activity, activated by sleep. Both patients had compound heterozygous RARS2 variants with likely impact on splicing and transcription. Remarkably, of the now 52 RARS2 variants reported in 54 patients, our reanalysis found that 44 (85%) have been shown to or are predicted to affect splicing or gene expression leading to protein truncation or nonsense-mediated decay. We expand the RARS2 phenotypic spectrum to include infantile encephalopathy and suggest this gene is enriched for pathogenic variants that disrupt splicing.

Somatic IDH1 variant (p.R132C) in an adult male with Maffucci syndrome.

Maffucci syndrome is a rare, highly variable somatic mosaic condition, and well-known cancer-related gain-of-function variants in either the IDH1 or IDH2 genes have been found in the affected tissues of most reported individuals. Features include benign enchondroma and spindle-cell hemangioma, with a recognized increased risk of various malignancies. Fewer than 200 affected individuals have been reported; therefore, accurate estimates of malignancy risk are difficult to quantify and recommended surveillance guidelines are not available. The same gain-of-function IDH1 and IDH2 variants are also implicated in a variety of other benign and malignant tumors. An adult male presented with several soft palpable lesions on the right upper limb. Imaging and histopathology raised the possibility of Maffucci syndrome. DNA was extracted from peripheral blood lymphocytes and tissue surgically resected from a spindle-cell hemangioma. Sanger sequencing and droplet digital polymerase chain reaction (PCR) analysis of the IDH1 gene were performed. We identified a somatic mosaic c.394C > T (p.R132C) variant in exon 5 of IDH1, in DNA derived from hemangioma tissue at ∼17% variant allele fraction. This variant was absent in DNA derived from blood. This variant has been identified in the affected tissue of most reported individuals with Maffucci syndrome. Although this individual has a potentially targetable variant, and there is a recognized risk of malignant transformation in this condition, a decision was made not to intervene with an IDH1 inhibitor. The reasons and prospects for therapy in this condition are discussed.

Pathogenic MAST3 Variants in the STK Domain Are Associated with Epilepsy.

OBJECTIVE: The MAST family of microtubule-associated serine-threonine kinases (STKs) have distinct expression patterns in the developing and mature human and mouse brain. To date, only MAST1 has been conclusively associated with neurological disease, with de novo variants in individuals with a neurodevelopmental disorder, including a mega corpus callosum. METHODS: Using exome sequencing, we identify MAST3 missense variants in individuals with epilepsy. We also assess the effect of these variants on the ability of MAST3 to phosphorylate the target gene product ARPP-16 in HEK293T cells. RESULTS: We identify de novo missense variants in the STK domain in 11 individuals, including 2 recurrent variants p.G510S (n = 5) and p.G515S (n = 3). All 11 individuals had developmental and epileptic encephalopathy, with 8 having normal development prior to seizure onset at <2 years of age. All patients developed multiple seizure types, 9 of 11 patients had seizures triggered by fever and 9 of 11 patients had drug-resistant seizures. In vitro analysis of HEK293T cells transfected with MAST3 cDNA carrying a subset of these patient-specific missense variants demonstrated variable but generally lower expression, with concomitant increased phosphorylation of the MAST3 target, ARPP-16, compared to wild-type. These findings suggest the patient-specific variants may confer MAST3 gain-of-function. Moreover, single-nuclei RNA sequencing and immunohistochemistry shows that MAST3 expression is restricted to excitatory neurons in the cortex late in prenatal development and postnatally. INTERPRETATION: In summary, we describe MAST3 as a novel epilepsy-associated gene with a potential gain-of-function pathogenic mechanism that may be primarily restricted to excitatory neurons in the cortex. ANN NEUROL 2021;90:274-284.

One-Stage, Limited-Resection Epilepsy Surgery for Bottom-of-Sulcus Dysplasia.

OBJECTIVE: To determine whether 1-stage, limited corticectomy controls seizures in patients with MRI-positive, bottom-of-sulcus dysplasia (BOSD). METHODS: We reviewed clinical, neuroimaging, electrocorticography (ECoG), operative, and histopathology findings in consecutively operated patients with drug-resistant focal epilepsy and MRI-positive BOSD, all of whom underwent corticectomy guided by MRI and ECoG. RESULTS: Thirty-eight patients with a median age at surgery of 10.2 (interquartile range [IQR] 6.0-14.1) years were included. BOSDs involved eloquent cortex in 15 patients. Eighty-seven percent of patients had rhythmic spiking on preresection ECoG. Rhythmic spiking was present in 22 of 24 patients studied with combined depth and surface electrodes, being limited to the dysplastic sulcus in 7 and involving the dysplastic sulcus and gyral crown in 15. Sixty-eight percent of resections were limited to the dysplastic sulcus, leaving the gyral crown. Histopathology was focal cortical dysplasia (FCD) type IIb in 29 patients and FCDIIa in 9. Dysmorphic neurons were present in the bottom of the sulcus but not the top or the gyral crown in 17 of 22 patients. Six (16%) patients required reoperation for postoperative seizures and residual dysplasia; reoperation was not correlated with ECoG, neuroimaging, or histologic abnormalities in the gyral crown. At a median 6.3 (IQR 4.8-9.9) years of follow-up, 33 (87%) patients are seizure-free, 31 off antiseizure medication. CONCLUSION: BOSD can be safely and effectively resected with MRI and ECoG guidance, corticectomy potentially being limited to the dysplastic sulcus, without need for intracranial EEG monitoring and functional mapping. CLASSIFICATION OF EVIDENCE: This study provides Class IV evidence that 1-stage, limited corticectomy for BOSD is safe and effective for control of seizures.

DRAXIN regulates interhemispheric fissure remodelling to influence the extent of corpus callosum formation.

Corpus callosum dysgenesis (CCD) is a congenital disorder that incorporates either partial or complete absence of the largest cerebral commissure. Remodelling of the interhemispheric fissure (IHF) provides a substrate for callosal axons to cross between hemispheres, and its failure is the main cause of complete CCD. However, it is unclear whether defects in this process could give rise to the heterogeneity of expressivity and phenotypes seen in human cases of CCD. We identify incomplete IHF remodelling as the key structural correlate for the range of callosal abnormalities in inbred and outcrossed BTBR mouse strains, as well as in humans with partial CCD. We identify an eight base-pair deletion in Draxin and misregulated astroglial and leptomeningeal proliferation as genetic and cellular factors for variable IHF remodelling and CCD in BTBR strains. These findings support a model where genetic events determine corpus callosum structure by influencing leptomeningeal-astroglial interactions at the IHF.

Resection of tuber centers only for seizure control in tuberous sclerosis complex.

Our previous studies suggest the tuber center is the seizure focus in tuberous sclerosis complex (TSC). We report findings from 5 epilepsy surgeries in 4 children with TSC and focal motor seizures from single tubers in primary sensorimotor cortex in which resection was limited to the cortex in the tuber center. Intraoperative electrocorticography showed epileptiform activity in the tuber center, with or without propagation to the tuber rim and surrounding perituberal cortex. Histopathology showed an abundance of dysmorphic neurons in the tuber center compared to the rim in four paired specimens, dysmorphic neurons being the reported epileptogenic cell line in TSC. Associated focal motor seizures were eliminated in all children (mean follow up 6.3 years) without postoperative deficits. Tuber center resections are a potential alternative to complete tuberectomy in patients with epileptogenic tubers in eloquent cortex and potentially also in children with a high tuber load and multifocal seizures.

Verbal Adynamia and Conceptualization in Partial Rhombencephalosynapsis and Corpus Callosum Dysgenesis.

Verbal adynamia is characterized by markedly reduced spontaneous speech that is not attributable to a core language deficit such as impaired naming, reading, repetition, or comprehension. In some cases, verbal adynamia is severe enough to be considered dynamic aphasia. We report the case of a 40-year-old, left-handed, male native English speaker who presented with partial rhombencephalosynapsis, corpus callosum dysgenesis, and a language profile that is consistent with verbal adynamia, or subclinical dynamic aphasia, possibly underpinned by difficulties selecting and generating ideas for expression. This case is only the second investigation of dynamic aphasia in an individual with a congenital brain malformation. It is also the first detailed neuropsychological report of an adult with partial rhombencephalosynapsis and corpus callosum dysgenesis, and the only known case of superior intellectual abilities in this context.

Early-onset vitamin B6-dependent epilepsy due to pathogenic PLPBP variants in a premature infant: A case report and review of the literature.

Vitamin B6-dependent epilepsies are a heterogeneous group of disorders characterized by decreased availability of the active cofactor pyridoxal-5'-phosphate (PLP). While pathogenic variants in ALDH7A1 or PNPO genes account for most cases of these disorders, biallelic pathogenic variants in PLPBP have been shown to cause a form of early onset vitamin B6-dependent epilepsy (EPVB6D). PLPBP is thought to play a role in the homeostatic regulation of vitamin B6, by supplying PLP to apoenzymes while limiting side-reaction toxicity related to excess unbound PLP. Neonatal-onset intractable seizures that respond to pyridoxine and/or PLP are a predominant feature of EPVB6D in humans. Unlike other causes of vitamin B6-dependent epilepsies; however, a specific biomarker for this disorder has yet to be identified. Here we present data from a premature infant found to have pathogenic variants in PLPBP and propose that prematurity may provide an additional clue for early consideration of this diagnosis. We discuss these findings in context of previously published genotypic, phenotypic, and metabolic data from similarly affected patients.

Genetic heterogeneity of polymicrogyria: study of 123 patients using deep sequencing.

Polymicrogyria is a malformation of cortical development characterized by overfolding and abnormal lamination of the cerebral cortex. Manifestations include epilepsy, speech disturbance and motor and cognitive disability. Causes include acquired prenatal insults and inherited and de novo genetic variants. The proportion of patients with polymicrogyria and a causative germline or mosaic variant is not known. The aim of this study was to identify the monogenic causes of polymicrogyria in a heterogeneous cohort of patients reflective of specialized referral services. Patients with polymicrogyria were recruited from two clinical centres in Australia and Belgium. Patients with evidence of congenital cytomegalovirus infection or causative chromosomal copy number variants were excluded. One hundred and twenty-three patients were tested using deep sequencing gene panels including known and candidate genes for malformations of cortical development. Causative and potentially causative variants were identified and correlated with phenotypic features. Pathogenic or likely pathogenic variants were identified in 25/123 (20.3%) patients. A candidate variant was identified for an additional patient but could not be confirmed as de novo, and therefore it was classified as being of uncertain significance with high clinical relevance. Of the 22 dominant variants identified, 5 were mosaic with allele fractions less than 0.33 and the lowest allele fraction 0.09. The most common causative genes were TUBA1A and PIK3R2. The other eleven causative genes were PIK3CA, NEDD4L, COL4A1, COL4A2, GPSM2, GRIN2B, WDR62, TUBB3, TUBB2B, ACTG1 and FH. A genetic cause was more likely to be identified in the presence of an abnormal head size or additional brain malformations suggestive of a tubulinopathy, such as dysmorphic basal ganglia. A gene panel test provides greater sequencing depth and sensitivity for mosaic variants than whole exome or genome sequencing but is limited to the genes included, potentially missing variants in newly discovered genes. The diagnostic yield of 20.3% indicates that polymicrogyria may be associated with genes not yet known to be associated with brain malformations, brain-specific somatic mutations or non-genetic causes.

Clinical seizure manifestations in the absence of synaptic connections.

We report a child with a history of temporal-parietal-occipital disconnection for epilepsy secondary to posterior quadrantic dysplasia who developed recurrent and prolonged bouts of distress and autonomic disturbance associated with EEG and PET evidence of status epilepticus confined to his disconnected cortex. These bouts were refractory to antiseizure medications but resolved following resection of the disconnected cortex. In the absence of synaptic connections, we hypothesise that his seizure-related symptoms were mediated either by neurochemical transmission in preserved vascular and lymphatic channels or by ephaptic transmission to trigeminal nerve fibres in overlying dura, producing symptoms akin to migraine. The case highlights potential means by which seizures may manifest clinically, without synaptic connections, and adds to the differential for symptoms post-disconnection surgery.

The severe epilepsy syndromes of infancy: A population-based study.

OBJECTIVE: To study the epilepsy syndromes among the severe epilepsies of infancy and assess their incidence, etiologies, and outcomes. METHODS: A population-based cohort study was undertaken of severe epilepsies with onset before age 18 months in Victoria, Australia. Two epileptologists reviewed clinical features, seizure videos, and electroencephalograms to diagnose International League Against Epilepsy epilepsy syndromes. Incidence, etiologies, and outcomes at age 2 years were determined. RESULTS: Seventy-three of 114 (64%) infants fulfilled diagnostic criteria for epilepsy syndromes at presentation, and 16 (14%) had "variants" of epilepsy syndromes in which there was one missing or different feature, or where all classical features had not yet emerged. West syndrome (WS) and "WS-like" epilepsy (infantile spasms without hypsarrhythmia or modified hypsarrhythmia) were the most common syndromes, with a combined incidence of 32.7/100 000 live births/year. The incidence of epilepsy of infancy with migrating focal seizures (EIMFS) was 4.5/100 000 and of early infantile epileptic encephalopathy (EIEE) was 3.6/100 000. Structural etiologies were common in "WS-like" epilepsy (100%), unifocal epilepsy (83%), and WS (39%), whereas single gene disorders predominated in EIMFS, EIEE, and Dravet syndrome. Eighteen (16%) infants died before age 2 years. Development was delayed or borderline in 85 of 96 (89%) survivors, being severe-profound in 40 of 96 (42%). All infants with EIEE or EIMFS had severe-profound delay or were deceased, but only 19 of 64 (30%) infants with WS, "WS-like," or "unifocal epilepsy" had severe-profound delay, and only two of 64 (3%) were deceased. SIGNIFICANCE: Three quarters of severe epilepsies of infancy could be assigned an epilepsy syndrome or "variant syndrome" at presentation. In this era of genomic testing and advanced brain imaging, diagnosing epilepsy syndromes at presentation remains clinically useful for guiding etiologic investigation, initial treatment, and prognostication.

Neurocognitive Dysfunction and Smaller Brain Volumes in Adolescents and Adults With a Fontan Circulation.

BACKGROUND: Neurocognitive outcomes beyond childhood in people with a Fontan circulation are not well defined. This study aimed to investigate neurocognitive functioning in adolescents and adults with a Fontan circulation and associations with structural brain injury, brain volumetry, and postnatal clinical factors. METHODS: In a binational study, participants with a Fontan circulation without a preexisting major neurological disability were prospectively recruited from the Australia and New Zealand Fontan Registry. Neurocognitive function was assessed by using Cogstate software in 107 participants with a Fontan circulation and compared with control groups with transposition of the great arteries (n=50) and a normal circulation (n=41). Brain MRI with volumetric analysis was performed in the participants with a Fontan circulation and compared with healthy control data from the ABIDE I and II (Autism Brain Imaging Data Exchange) and PING (Pediatric Imaging, Neurocognition, and Genetics) data repositories. Clinical data were retrospectively collected. RESULTS: Of the participants with a Fontan circulation who had a neurocognitive assessment, 55% were male and the mean age was 22.6 years (SD 7.8). Participants with a Fontan circulation performed worse in several areas of neurocognitive function compared with those with transposition of the great arteries and healthy controls (P<0.05). Clinical factors associated with worse neurocognitive outcomes included more inpatient days during childhood, younger age at Fontan surgery, and longer time since Fontan procedure (P<0.05). Adults with a Fontan circulation had more marked neurocognitive dysfunction than adolescents with a Fontan circulation in 2 domains (psychomotor function, P=0.01 and working memory, P=0.02). Structural brain injury was present in the entire Fontan cohort; the presence of white matter injury was associated with worse paired associate learning (P<0.001), but neither the presence nor severity of infarct, subcortical gray matter injury, and microhemorrhage was associated with neurocognitive outcomes. Compared with healthy controls, people with a Fontan circulation had smaller global brain volumes (P<0.001 in all regions) and smaller regional brain volumes in most cerebral cortical regions (P<0.05). Smaller global brain volumes were associated with worse neurocognitive functioning in several domains (P<0.05). A significant positive association was also identified between global brain volumes and resting oxygen saturations (P≤0.04). CONCLUSIONS: Neurocognitive impairment is common in adolescents and adults with a Fontan circulation and is associated with smaller gray and white matter brain volume. Understanding modifiable factors that contribute to brain injury to optimize neurocognitive function is paramount.

NEXMIF encephalopathy: an X-linked disorder with male and female phenotypic patterns.

PURPOSE: Pathogenic variants in the X-linked gene NEXMIF (previously KIAA2022) are associated with intellectual disability (ID), autism spectrum disorder, and epilepsy. We aimed to delineate the female and male phenotypic spectrum of NEXMIF encephalopathy. METHODS: Through an international collaboration, we analyzed the phenotypes and genotypes of 87 patients with NEXMIF encephalopathy. RESULTS: Sixty-three females and 24 males (46 new patients) with NEXMIF encephalopathy were studied, with 30 novel variants. Phenotypic features included developmental delay/ID in 86/87 (99%), seizures in 71/86 (83%) and multiple comorbidities. Generalized seizures predominated including myoclonic seizures and absence seizures (both 46/70, 66%), absence with eyelid myoclonia (17/70, 24%), and atonic seizures (30/70, 43%). Males had more severe developmental impairment; females had epilepsy more frequently, and varied from unaffected to severely affected. All NEXMIF pathogenic variants led to a premature stop codon or were deleterious structural variants. Most arose de novo, although X-linked segregation occurred for both sexes. Somatic mosaicism occurred in two males and a family with suspected parental mosaicism. CONCLUSION: NEXMIF encephalopathy is an X-linked, generalized developmental and epileptic encephalopathy characterized by myoclonic-atonic epilepsy overlapping with eyelid myoclonia with absence. Some patients have developmental encephalopathy without epilepsy. Males have more severe developmental impairment. NEXMIF encephalopathy arises due to loss-of-function variants.

Neuronal ceroid lipofuscinosis type 2: an Australian case series.

AIM: Late infantile neuronal ceroid lipofuscinosis type 2 (CLN2) disease is a rare neurodegenerative disorder presenting in children aged 2-4 years with seizures and loss of motor and language skills, followed by blindness and death in late childhood. Initial presenting features are similar to a range of common epilepsies. We aim to highlight typical clinical and radiological features that may prompt diagnosis of CLN2 disease in early disease stages. METHODS: We present a series of 13 Australian patients with CLN2 disease, describing clinical features, disease evolution, neuroimaging, electroencephalogram, biochemical and genetic results. Expert neuroradiological magnetic resonance imaging (MRI) analysis was retrospectively performed on 10 cases. RESULTS: Twelve patients presented with seizures, with initial seizures being focal (n = 4), generalised tonic-clonic (n = 3), absence (n = 3) and febrile (n = 2). Eleven patients (85%) had a language delay before the onset of seizures. Cerebellar or cerebral atrophy was noted in all patients on centralised MRI review, with abnormalities of the brain-stem, ventricles, corpus callosum and hippocampi. CONCLUSIONS: Early language delay with the onset of seizures at 2-4 years of age is the hallmark of CLN2 disease. MRI findings of early subtle atrophy in the cerebellum or posterior cortical regions should hasten testing for CLN2 disease to enable early initiation of enzyme replacement therapy.

EML1-associated brain overgrowth syndrome with ribbon-like heterotopia.

EML1 encodes the protein Echinoderm microtubule-associated protein-like 1 or EMAP-1 that binds to the microtubule complex. Mutations in this gene resulting in complex brain malformations have only recently been published with limited clinical descriptions. We provide further clinical and imaging details on three previously published families, and describe two novel unrelated individuals with a homozygous partial EML1 deletion and a homozygous missense variant c.760G>A, p.(Val254Met), respectively. From review of the clinical and imaging data of eight individuals from five families with biallelic EML1 variants, a very consistent imaging phenotype emerges. The clinical syndrome is characterized by mainly neurological features including severe developmental delay, drug-resistant seizures and visual impairment. On brain imaging there is megalencephaly with a characteristic ribbon-like subcortical heterotopia combined with partial or complete callosal agenesis and an overlying polymicrogyria-like cortical malformation. Several of its features can be recognized on prenatal imaging especially the abnormaly formed lateral ventricles, hydrocephalus (in half of the cases) and suspicion of a neuronal migration disorder. In conclusion, biallelic EML1 disease-causing variants cause a highly specific pattern of congenital brain malformations, severe developmental delay, seizures and visual impairment.

Epidemiology and etiology of infantile developmental and epileptic encephalopathies in Tasmania.

We sought to determine incidence, etiologies, and yield of genetic testing in infantile onset developmental and epileptic encephalopathies (DEEs) in a population isolate, with an intensive multistage approach. Infants born in Tasmania between 2011 and 2016, with seizure onset <2 years of age, epileptiform EEG, frequent seizures, and developmental impairment, were included. Following review of EEG databases, medical records, brain MRIs, and other investigations, clinical genetic testing was undertaken with subsequent research interrogation of whole exome sequencing (WES) in unsolved cases. The incidence of infantile DEEs was 0.44/1000 per year (95% confidence interval 0.25 to 0.71), with 16 cases ascertained. The etiology was structural in 5/16 cases. A genetic basis was identified in 6 of the remaining 11 cases (3 gene panel, 3 WES). In two further cases, WES identified novel variants with strong in silico data; however, paternal DNA was not available to support pathogenicity. The etiology was not determined in 3/16 (19%) cases, with a candidate gene identified in one of these. Pursuing clinical imaging and genetic testing followed by WES at an intensive research level can give a high diagnostic yield in the infantile DEEs, providing a solid base for prognostic and genetic counseling.