BACKGROUND:Developmental and epileptic encephalopathy (DEE) includes diseases where there is developmental impairment related to both the underlying etiology independent of epileptiform activity and the epileptic encephalopathy. Patients often present with movement disorders (MD). This study aims to delineate the motor phenotype in a cohort of patients with DEE. METHODS:Retrospective review of 82 patients with DEE. MD type and distribution were documented and when available, video recordings were reviewed. RESULTS:Patients were classified into five etiological groups: 30.5 % had a likely genetic diagnosis, 29.3 % a confirmed genetic diagnosis, 18.3 % an inborn error of metabolism (IEM), 14.6 % an acquired brain lesion, and 7.3 % a brain dysplasia. Hyperkinetic MDs were present in 85.4 % of patients, including dystonia (48.8 %), stereotypies (22.0 %), chorea (20.7 %), hyperekplexia (15.9 %), tremor (14.6 %), and myoclonus (6.1 %). Parkinsonism was observed in 11 % of patients, ataxia in 8.5 % and multiple MDs in 50 %. Paroxysmal episodes of MD exacerbation occurred in 6 patients, and transient MD in 8. Dystonia was most frequent in patients with acquired brain lesions (p = 0.003). Parkinsonism was more frequent in patients with brain dysplasias and IEM (p = 0.043). CONCLUSIONS:This study confirms the high frequency of hyperkinetic and combined MD in DEE, and identifies characteristic MDs in conditions such SCN8A, FOXG1 and ARX related DEE, as well as ataxia and tremor in STXBP1, SCN1A, MTRFR, KCTD7 and 15q111-13 deletion. Novel observations, include the occurrence of paroxysmal dyskinetic exacerbations in FOXG1, axial stereotypies in KCNQ2, hyperekplexia in cortical dysplasia and Parkinsonism in ECHS1 with DEE.

Many neurodevelopmental defects are linked to genes involved in housekeeping functions, such as those encoding ribosome biogenesis factors. How reductions in ribosome biogenesis can result in tissue- and developmental-specific defects remains unclear. Here we describe variants in the ribosome biogenesis factor AIRIM/C1orf109 that are primarily associated with neurodevelopmental disorders. Using human cerebral organoids in combination with proteomic, single-cell RNA sequencing and single-organoid translation analyses, we identify a previously unappreciated drop in protein production during early brain development. We find that ribosome levels decrease during neuroepithelial differentiation, making differentiating cells particularly vulnerable to perturbations in ribosome biogenesis during this time. Reduced ribosome availability more profoundly impacts the translation of specific transcripts, disrupting both survival and cell fate commitment of transitioning neuroepithelia. Enhancing mTOR activity suppresses the growth and developmental defects associated with AIRIM/C1orf109 variants. This work provides evidence for the functional importance of regulated changes in global protein synthesis capacity during cellular differentiation.

Oculopharyngeal muscular dystrophy (OPMD) is a rare, adult-onset, autosomal dominant myopathy characterized by variability in the age of onset and disease progression. However, its pathogenesis and phenotypic variability remain poorly understood. The disorder is caused by an expansion of a short polyalanine tract in the poly(A) binding protein nuclear 1 (PABPN1) gene. This study presents data from 23 patients across 19 Greek families with pathogenic PABPN1 expansions, including demographic and laboratory data, as well as molecular and electron microscopy findings. Eight distinct trinucleotide expansion genotypes were identified. Electron microscopy consistently demonstrated mitochondrial abnormalities, including swelling, disrupted cristae and atypical lipid inclusions. Clinical heterogeneity was observed at both inter- and intrafamilial levels, and milder phenotypes were generally linked to smaller alleles. Notably, maternally inherited expansions were associated with an earlier disease onset and more severe progression in affected offspring. Given the genetic variability observed in the cohort, the presence of a founder effect could not be supported. A significant degree of underdiagnosis or diagnostic delay was noted, largely attributable to the rarity and clinical heterogeneity of the disease. The observed intrafamilial heterogeneity - particularly in maternally inherited expansions - supports previous reports suggesting that mitochondrial dysfunction may contribute to transgenerational disease progression in the context of a dominant, causative nuclear variant.

WDR91, a WD40 repeat domain-containing protein, is a key regulator of endosomal trafficking, lysosomal function, and autophagy. It acts as a Rab7 effector, forming a complex with WDR81 to modulate phosphatidylinositol 3-kinase (PI3K) activity, endosomal maturation, and lysosome homeostasis. Loss-of-function variants in WDR91 are considered related to endosomal accumulation, impaired cargo degradation, and neurodegeneration. In this report, an autosomal recessive neurodevelopmental disorder is proposed, associated with WDR91 loss-of-function in a consanguineous family. The patient presented with severe microcephaly, dysmorphic features, and organomegaly, along with early onset psychomotor delay, hypotonia, sensorineural hearing impairment, and visual impairment. Whole-exome sequencing (WES) identified a homozygous splice site variant, NM_014149.4:c.1395+1G>A, predicted to disrupt the donor site and classified as likely pathogenic (PVS1, PM2). The variant was absent from population databases and our internal in-house cohort. Functional analysis supports a pathogenic role for the variant. WDR91 deficiency results in neuronal loss, cortical thinning, and impaired brain development, as evidenced in Wdr91 knockout models. Our study expands the clinical and genetic spectrum of WDR91-related disorders and highlights the need for further investigations to elucidate the precise molecular mechanisms underlying WDR91-associated pathogenesis.

Transmembrane protein 184B (TMEM184B) is an endosomal 7-pass transmembrane protein with evolutionarily conserved roles in synaptic structure and axon degeneration. We report six pediatric cases who have de novo heterozygous variants in TMEM184B; five individuals harbor a rare missense variant, and one individual has an mRNA splice site change. This cohort is unified by overlapping neurodevelopmental deficits including developmental delay, corpus callosum hypoplasia, seizures, and/or microcephaly. TMEM184B is predicted to contain a pore domain wherein four of five human disease-associated missense variants cluster. Structural modeling suggests that all missense variants alter TMEM184B protein stability. To understand the contribution of TMEM184B to neural development in vivo, we knocked down the TMEM184B ortholog in zebrafish and observed microcephaly and reduced anterior commissural axons, aligning with symptoms of affected individuals. Ectopic expression of TMEM184B c.550A>G (p.Lys184Glu) and c.484G>A (p.Gly162Arg) variants cause reduced head size and body length, indicating dominant effects, while three other variants show haploinsufficiency. None of the variants are able to rescue the knockdown phenotype. Human induced pluripotent stem cells with monoallelic production of p.Lys184Glu show mRNA disruptions in key metabolic pathways including those controlling mechanistic target of rapamycin activity. Expression of p.Lys184Glu and c.863G>C (p.Gly288Ala) increased apoptosis in cell lines, and p.Lys184Glu increased nuclear localization of transcription factor EB, consistent with a cellular starvation state. Together, our data indicate that TMEM184B variants cause cellular metabolic disruption and result in abnormal neural development.

Background: Fanconi Anemia (FA) is a rare disorder, characterized by chromosomal instability, congenital abnormalities, progressive bone marrow failure, and predisposition to cancer. FA is caused by pathogenic variants in any of the 23 (FANCA-FANCY) linked genes. Procedure: Retrospective analysis of 13 FA patients with a causative variant was performed. Patients (6 boys and 7 girls) aged from 9 to 26 years old, (mean age of 7.3 years), at diagnosis. Results: Phenotype evaluation demonstrated in 11/13 patients’ congenital anomalies, with pigmentary changes and short stature, present in 90% of cases. Hematological abnormalities were present in 10/11 patients, with thrombocytopenia being the prominent finding. Genetic analysis for the most common complementation group FA-A revealed that 12/13 patients belonged to this group and only one patient was found to be FA-E. Exon deletions, single nucleotide variations, and duplications were identified. Familial patterns, due to consanguinity, were evident in one case. Twelve patients underwent hematopoietic stem cell transplantation (HSCT), with variable pre-HSCT supportive treatments. Post-HSCT data showed that 9 out of 10 patients for whom follow up data was available, survived for a median time of 5.4 years. Complications like acute graft-versus-host disease were noted. Conclusions: Our study highlights the importance of genotype towards tailored monitoring for children and families with FA.

INTRODUCTION/AIMS:Myotonia congenita (MC) is the most common hereditary channelopathy in humans. Characterized by muscle stiffness, MC may be transmitted as either an autosomal dominant (Thomsen) or a recessive (Becker) disorder. MC is caused by variants in the voltage-gated chloride channel 1 (CLCN1) gene, important for the normal repolarization of the muscle action potential. More than 250 disease-causing variants in the CLCN1 gene have been reported. This study provides an MC genotype-phenotype spectrum in a large cohort of Greek patients and focuses on novel variants and disease epidemiology, including additional insights for the variant CLCN1:c.501C > G. METHODS:Sanger sequencing for the entire coding region of the CLCN1 gene was performed. Targeted segregation analysis of likely candidate variants in additional family members was performed. Variant classification was based on American College of Medical Genetics (ACMG) guidelines. RESULTS:Sixty-one patients from 47 unrelated families were identified, consisting of 51 probands with Becker MC (84%) and 10 with Thomsen MC (16%). Among the different variants detected, 11 were novel and 16 were previously reported. The three most prevalent variants were c.501C > G, c.2680C > T, and c.1649C > G. Additionally, c.501C > G was detected in seven Becker cases in-cis with the c.1649C > G. DISCUSSION:The large number of patients in whom a diagnosis was established allowed the characterization of genotype-phenotype correlations with respect to both previously reported and novel findings. For the c.501C > G (p.Phe167Leu) variant a likely nonpathogenic property is suggested, as it only seems to act as an aggravating modifying factor in cases in which a pathogenic variant triggers phenotypic expression.