DEPDC5 (DEP Domain-Containing Protein 5) encodes an inhibitory component of the mammalian target of rapamycin (mTOR) pathway and is commonly implicated in sporadic and familial focal epilepsies, both non-lesional and in association with focal cortical dysplasia. Germline pathogenic variants are typically heterozygous and inactivating. We describe a novel phenotype caused by germline biallelic missense variants in DEPDC5. Cases were identified clinically. Available records, including magnetic resonance imaging and electroencephalography, were reviewed. Genetic testing was performed by whole exome and whole-genome sequencing and cascade screening. In addition, immunohistochemistry was performed on skin biopsy. The phenotype was identified in nine children, eight of which are described in detail herein. Six of the children were of Irish Traveller, two of Tunisian and one of Lebanese origin. The Irish Traveller children shared the same DEPDC5 germline homozygous missense variant (p.Thr337Arg), whereas the Lebanese and Tunisian children shared a different germline homozygous variant (p.Arg806Cys). Consistent phenotypic features included extensive bilateral polymicrogyria, congenital macrocephaly and early-onset refractory epilepsy, in keeping with other mTOR-opathies. Eye and cardiac involvement and severe neutropenia were also observed in one or more patients. Five of the children died in infancy or childhood; the other four are currently aged between 5 months and 6 years. Skin biopsy immunohistochemistry was supportive of hyperactivation of the mTOR pathway. The clinical, histopathological and genetic evidence supports a causal role for the homozygous DEPDC5 variants, expanding our understanding of the biology of this gene.

Background. Autoimmune encephalitis (AE) is a rapidly progressive encephalopathy caused by antibodies targeting neurons in the central nervous system generating specific immune responses. It is increasingly recognized in children. Objective. To describe clinical, neuroimaging, and laboratory features, treatment, and outcome in a cohort of Tunisian children with AE. Methods. We conducted a retrospective review of the medical records of all children attending the Department of Child and Adolescent Neurology (Tunis) with autoimmune encephalitis between 2004 and 2020. Clinical, neuroimaging, laboratory features, therapeutic data, and outcome were analyzed. Results. Nineteen children were included in the study (12 girls and 7 boys). The median age at diagnosis was 7.68 years (range: 10 months-13 years). The most frequent manifestations were seizures and behavioral disorders. Eleven cases were diagnosed with anti-NMDA receptor encephalitis, 4 cases with anti-Ma2 encephalitis, 3 cases with anti-GAD encephalitis, and 1 case with anti-SOX1 encephalitis. Brain MRI showed increased T2 and fluid-attenuated inversion recovery (FLAIR) signal of the temporal lobe in 5 patients. Eighteen patients showed improvement following first-line immunotherapy (high-dose corticosteroids, intravenous immunoglobulin). One patient with anti-GAD encephalitis died despite escalating immunotherapy. Conclusion. Diagnosis of autoimmune encephalitis is challenging in children, because of misleading presentations. An early and accurate diagnosis is important to enable proper therapeutic interventions.

Myasthenia gravis (MG) with antibodies to the muscle-specific tyrosine kinase (MuSK-MG) receptor is a rare entity. It represents 5 to 8% of all MG patients. Few pediatric cases were reported. Clinical presentation is often atypical. It is characterized by predominant involvement of cranial, bulbar, and axial muscles and early respiratory crises. Myokymia and fasciculation are suggestive of MuSK-MG. The clinical course of patients with MuSK-MG is worse than other types of MG. Responses to standard therapies are variable. We report clinical, neurophysiological, serological, and outcome profile of a Tunisian child with MuSK-MG.

GRIA‐related disorders arise from disease‐causing variants in GRIA1, GRIA2, GRIA3, or GRIA4 that encode α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionic acid (AMPA)‐type glutamate receptors (AMPARs). Rare monoallelic GRIA1–4 variants affecting AMPAR function can potentially lead to neurodevelopmental disorders. The impact on AMPAR function may manifest as either gain‐of‐function (GOF) or loss‐of‐function (LOF). We recruited nine unrelated patients with either known disease‐causing GOF variants in GRIA3 at position p.Gly803 or variants at the paralogous position in GRIA2 (p.Gly792). Specifically, five patients carried a de novo GRIA3 variant (p.Gly803Glu or p.Gly803Val), one carried a maternally inherited GRIA3 variant (p.Gly803Ala) and three carried de novo GRIA2 variants (p.Gly792Arg, p.Gly792Val, or p.Gly792Glu) which we demonstrate are also GOF. Recurrent symptoms included developmental delay affecting both motor skills and language abilities; cognitive impairment; behavioral and psychiatric comorbidities; hypertonia, cerebral palsy, non‐epileptic myoclonus, and treatment‐resistant epilepsy. We also provide insights into social skills, levels of autonomy, living arrangements, and educational attainment. We compared the clinical features associated with the two paralogous GOF GRIA2 and GRIA3 variants. Our study elucidates the developmental aspects, cognitive abilities, seizure profiles, and behavioral challenges associated with these variants and contributes to advancing our understanding and treatment of patients affected by this rare condition.

ATP1A3 mutations have now been recognized in infants, children, and adults presenting with a diverse group of neurological phenotypes, including rapid-onset dystonia-parkinsonism, alternating hemiplegia of childhood, and most recently, cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural hearing loss syndrome. The phenotypic spectrum of ATP1A3-related neurological disorders continues to expand. In this case study, we report on early life epilepsy with episodic apnea potentially secondary to ATP1A3 mutation in a Tunisian child.

Kohlschütter‐Tönz Syndrome (KTS) is an ultra‐rare autosomal recessive disorder, characterized by a clinical triad: infantile‐onset epilepsy, global developmental delay, and amelogenesis imperfecta. KTS is caused by pathogenic variants in ROGDI, encoding a leucine zipper protein of unknown function. Our study characterizes a novel homozygous ROGDI variant (NM_024589.3:c.646‐2A>G) identified in a Tunisian family case with KTS, renal tubular acidosis, and hyperammonemia. This variant disrupts a canonical acceptor splice site (ASS) in intron 8. Reverse‐transcriptase polymerase chain reaction and targeted long‐read cDNA sequencing, identified only abnormal transcripts secondary to the ROGDI ASS variant in the proband. Complex splicing events were detected including exon 9 skipping, cryptic ASS activation leading to 13‐bp deletion in exon 9, and retention of intron 8 or both intron 8 and 9. These alterations were all predicted to result in nonsense mediated decay and ROGDI loss of function. By integrating complementary techniques, our study unveiled fundamental mechanisms underlying complex splice alterations, providing insights that may guide future therapeutic strategies in KTS.