Refining of the electroclinical phenotype in familial and sporadic cases of CSNK2B-related Neurodevelopmental Syndrome.

CSNK2B encodes a regulatory subunit of casein kinase II, which is highly expressed in the brain. Heterozygous pathogenic variants in CSNK2B are associated with Poirier-Bienvenu neurodevelopmental syndrome (POBINDS) (OMIM #618732), characterized by facial dysmorphisms, seizures, intellectual disability, and behavioral disturbances. We report ten new patients with CSNK2B-related Neurodevelopmental Syndrome associated with heterozygous variants of CSNK2B. In three patients, a pathogenic variant was inherited from an affected parent. We describe both molecular and clinical features, focusing on epileptic and neurodevelopmental phenotypes. The median age at follow-up was 8.5 years (range 21 months-42 years). All patients had epilepsy, with onset at a median age of 10.5 months range 6 days-10 years). Seizures were both focal and generalized and were resistant to anti-seizure medications in two out of ten patients. Six patients had mild to moderate cognitive delays, whereas four patients had no cognitive disability. Although all previously reported patients had a de novo CSNK2B pathogenic variant, here we report, for the first time, two familial cases of CSNK2B-related Neurodevelopmental Syndrome. We confirmed the highly variable expressivity of the disease among both interfamilial and intrafamilial cases. Furthermore, this study provides information about the long-term outcome in adult patients and underlines the importance of detailed family history collection before performing genetic testing in patients with epilepsy and neurodevelopmental disorders.

Hypoventilation and sleep hypercapnia in a case of congenital variant-like Rett syndrome.

BACKGROUND: Breathing disturbances are often a primary clinical concern especially during wakefulness of the classic form of Rett syndrome, but data for atypical forms are lacking. CASE PRESENTATION: We report the case of a 20-month-old female affected by Rett syndrome with congenital variant-like onset, characterized by severe hypotonia and neurodevelopment impairment. She presented hypoventilation, persistent periodic breathing, and sustained desaturation during sleep, without obstructive or mixed events. Pulse oximetry and capnography during wakefulness were strictly normal. To the best of our knowledge, this is the first case of a patient affected by a congenital variant of Rett syndrome presenting sleep hypercapnia. Hypotonia may play a major role in the genesis of hypoventilation and hypoxemia in our patient. Non-invasive ventilation led to quality-of-life improvements. CONCLUSIONS: Thus, we suggest screening patients with congenital-like Rett syndrome through transcutaneous bedtime carbon dioxide and oxygen monitoring. Moreover, assisted control mode was a breakthrough to achieve adequate ventilation in our case.

"Atypical" Krabbe disease in two siblings harboring biallelic GALC mutations including a deep intronic variant.

Krabbe disease (KD) is a rare lysosomal storage disorder caused by biallelic pathogenic variants in GALC. Most patients manifest the severe classic early-infantile form, while a small percentage of cases have later-onset types. We present two siblings with atypical clinical and neuroimaging phenotypes, compared to the classification of KD, who were found to carry biallelic loss-of-function GALC variants, including a recurrent 30 kb deletion and a previously unreported deep intronic variant that was identified by mRNA sequencing. This family represents a unique description in the KD literature and contributes to expanding the clinical and molecular spectra of this rare disorder.

A Novel KCNA2 Variant in a Patient with Non-Progressive Congenital Ataxia and Epilepsy: Functional Characterization and Sensitivity to 4-Aminopyridine.

Kv1.2 channels, encoded by the KCNA2 gene, are localized in the central and peripheral nervous system, where they regulate neuronal excitability. Recently, heterozygous mutations in KCNA2 have been associated with a spectrum of symptoms extending from epileptic encephalopathy, intellectual disability, and cerebellar ataxia. Patients are treated with a combination of antiepileptic drugs and 4-aminopyridine (4-AP) has been recently trialed in specific cases. We identified a novel variant in KCNA2, E236K, in a Serbian proband with non-progressive congenital ataxia and early onset epilepsy, treated with sodium valproate. To ascertain the pathogenicity of E236K mutation and to verify its sensitivity to 4-AP, we transfected HEK 293 cells with Kv1.2 WT or E236K cDNAs and recorded potassium currents through the whole-cell patch-clamp. In silico analysis supported the electrophysiological data. E236K channels showed voltage-dependent activation shifted towards negative potentials and slower kinetics of deactivation and activation compared with Kv1.2 WT. Heteromeric Kv1.2 WT+E236K channels, resembling the condition of the heterozygous patient, confirmed a mixed gain- and loss-of-function (GoF/LoF) biophysical phenotype. 4-AP inhibited both Kv1.2 and E236K channels with similar potency. Homology modeling studies of mutant channels suggested a reduced interaction between the residue K236 in the S2 segment and the gating charges at S4. Overall, the biophysical phenotype of E236K channels correlates with the mild end of the clinical spectrum reported in patients with GoF/LoF defects. The response to 4-AP corroborates existing evidence that KCNA2-disorders could benefit from variant-tailored therapeutic approaches, based on functional studies.

Expanding the Clinical and Mutational Spectrum of the PLP1-Related Hypomyelination of Early Myelinated Structures (HEMS).

The PLP1 gene, located on chromosome Xq22, encodes the proteolipid protein 1 and its isoform DM20. Mutations in PLP1 cause a spectrum of white matter disorders of variable severity. Here we report on four additional HEMS patients from three families harboring three novel PLP1 mutations in exon 3B detected by targeted next-generation sequencing. Patients experienced psychomotor delay or nystagmus in the first year of age and then developed ataxic-spastic or ataxic syndrome, compatible with a phenotype of intermediate severity in the spectrum of PLP1-related disorders. Regression occurred at the beginning of the third decade of the eldest patient. Extrapyramidal involvement was rarely observed. Brain MRI confirmed the involvement of structures that physiologically myelinate early, although the pattern of abnormalities may differ depending on the age at which the study is performed. These new cases contribute to expanding the phenotypic and genotypic spectrum of HEMS. Additional studies, especially enriched by systematic functional evaluations and long-term follow-up, are welcome to better delineate the natural history of this rare hypomyelinating leukodystrophy.

Heterozygous KIF1A variants underlie a wide spectrum of neurodevelopmental and neurodegenerative disorders.

BACKGROUND: Dominant and recessive variants in the KIF1A gene on chromosome 2q37.3 are associated with several phenotypes, although only three syndromes are currently listed in the OMIM classification: hereditary sensory and autonomic neuropathy type 2 and spastic paraplegia type 30, both recessively inherited, and mental retardation type 9 with dominant inheritance. METHODS: In this retrospective multicentre study, we describe the clinical, neuroradiological and genetic features of 19 Caucasian patients (aged 3-65 years) harbouring heterozygous KIF1A variants, and extensively review the available literature to improve current classification of KIF1A-related disorders. RESULTS: Patients were divided into two groups. Group 1 comprised patients with a complex phenotype with prominent pyramidal signs, variably associated in all but one case with additional features (ie, epilepsy, ataxia, peripheral neuropathy, optic nerve atrophy); conversely, patients in group 2 presented an early onset or congenital ataxic phenotype. Fourteen different heterozygous missense variants were detected by next-generation sequencing screening, including three novel variants, most falling within the kinesin motor domain. CONCLUSION: The present study further enlarges the clinical and mutational spectrum of KIF1A-related disorders by describing a large series of patients with dominantly inherited KIF1A pathogenic variants ranging from pure to complex forms of hereditary spastic paraparesis/paraplegias (HSP) and ataxic phenotypes in a lower proportion of cases. A comprehensive review of the literature indicates that KIF1A screening should be implemented in HSP regardless of its mode of inheritance or presentations as well as in other complex neurodegenerative or neurodevelopmental disorders showing congenital or early onset ataxia.

Movement disorders in ADAR1 disease: Insights from a comprehensive cohort.

ADAR1 variants are associated to rare and heterogenous neurological conditions, including Aicardi-Goutières syndrome type 6, bilateral striatal necrosis, and dyschromatosis symmetrica hereditaria. Movement disorders (MDs) commonly occur in ADAR1-related diseases although a complete overview on the phenomenology has not been provided yet. Here, a cohort of 57 patients with ADAR1-related diseases, including 3 unpublished patients and 54 previously reported cases, was reviewed. Data on demographics, clinical features of MDs, genetics and biomarkers were collected and descriptive statistics, group analysis for genotype and logistic regression were run. Manifestations of MD characterized the onset of ADAR1-related disease in 60% of patients. Specifically, dystonia occurred in 39% of cases, even as severe status dystonicus, while prevalence of other MDs was lower. Patients often presented brain lesions (>90%) and progressive disease course (43%), fatal in some cases. Clinical presentation and outcome differed among patients with distinct genotype. This review shows that phenomenology of MDs in ADAR1-related diseases is wide and heterogeneous, although a severe motor syndrome (often characterized by dystonia) secondary to brain lesions represents the most common manifestation. Waiting for future development of disease-modifying treatments, an appropriate symptomatic intervention is crucial for ADAR1 patients. Accordingly, a deeper knowledge of phenomenology is fundamental.

Mitochondrial and Peroxisomal Alterations Contribute to Energy Dysmetabolism in Riboflavin Transporter Deficiency.

Riboflavin transporter deficiency (RTD) is a childhood-onset neurodegenerative disorder characterized by progressive pontobulbar palsy, sensory and motor neuron degeneration, sensorineural hearing loss, and optic atrophy. As riboflavin (RF) is the precursor of FAD and FMN, we hypothesize that both mitochondrial and peroxisomal energy metabolism pathways involving flavoproteins could be directly affected in RTD, thus impacting cellular redox status. In the present work, we used induced pluripotent stem cells (iPSCs) from RTD patients to investigate morphofunctional features, focusing on mitochondrial and peroxisomal compartments. Using this model, we document the following RTD-associated alterations: (i) abnormal colony-forming ability and loss of cell-cell contacts, revealed by light, electron, and confocal microscopy, using tight junction marker ZO-1; (ii) mitochondrial ultrastructural abnormalities, involving shape, number, and intracellular distribution of the organelles, as assessed by focused ion beam/scanning electron microscopy (FIB/SEM); (iii) redox imbalance, with high levels of superoxide anion, as assessed by MitoSOX assay accompanied by abnormal mitochondrial polarization state, evaluated by JC-1 staining; (iv) altered immunofluorescence expression of antioxidant systems, namely, glutathione, superoxide dismutase 1 and 2, and catalase, as assessed by quantitatively evaluated confocal microscopy; and (v) peroxisomal downregulation, as demonstrated by levels and distribution of fatty acyl ß-oxidation enzymes. RF supplementation results in amelioration of cell phenotype and rescue of redox status, which was associated to improved ultrastructural features of mitochondria, thus strongly supporting patient treatment with RF, to restore mitochondrial- and peroxisomal-related aspects of energy dysmetabolism and oxidative stress in RTD syndrome.

Clinical and Genetic Overview of Paroxysmal Movement Disorders and Episodic Ataxias.

Paroxysmal movement disorders (PMDs) are rare neurological diseases typically manifesting with intermittent attacks of abnormal involuntary movements. Two main categories of PMDs are recognized based on the phenomenology: Paroxysmal dyskinesias (PxDs) are characterized by transient episodes hyperkinetic movement disorders, while attacks of cerebellar dysfunction are the hallmark of episodic ataxias (EAs). From an etiological point of view, both primary (genetic) and secondary (acquired) causes of PMDs are known. Recognition and diagnosis of PMDs is based on personal and familial medical history, physical examination, detailed reconstruction of ictal phenomenology, neuroimaging, and genetic analysis. Neurophysiological or laboratory tests are reserved for selected cases. Genetic knowledge of PMDs has been largely incremented by the advent of next generation sequencing (NGS) methodologies. The wide number of genes involved in the pathogenesis of PMDs reflects a high complexity of molecular bases of neurotransmission in cerebellar and basal ganglia circuits. In consideration of the broad genetic and phenotypic heterogeneity, a NGS approach by targeted panel for movement disorders, clinical or whole exome sequencing should be preferred, whenever possible, to a single gene approach, in order to increase diagnostic rate. This review is focused on clinical and genetic features of PMDs with the aim to (1) help clinicians to recognize, diagnose and treat patients with PMDs as well as to (2) provide an overview of genes and molecular mechanisms underlying these intriguing neurogenetic disorders.

Hereditary spastic paraplegia is a novel phenotype for germline de novo ATP1A1 mutation.

Dominant mutations in ATP1A1, encoding the alpha-1 isoform of the Na+ /K+ -ATPase, have been recently reported to cause an axonal to intermediate type of Charcot-Marie-Tooth disease (ie, CMT2DD) and a syndrome with hypomagnesemia, intractable seizures and severe intellectual disability. Here, we describe the first case of hereditary spastic paraplegia (HSP) caused by a novel de novo (p.L337P) variant in ATP1A1. We provide evidence for the causative role of this variant with functional and homology modeling studies. This finding expands the phenotypic spectrum of the ATP1A1-related disorders, adds a piece to the larger genetic puzzle of HSP, and increases knowledge on the molecular mechanisms underlying inherited axonopathies (ie, CMT and HSP).

Diagnostic Yield of a Targeted Next-Generation Sequencing Gene Panel for Pediatric-Onset Movement Disorders: A 3-Year Cohort Study.

In recent years, genetic techniques of diagnosis have shown rapid development, resulting in a modified clinical approach to many diseases, including neurological disorders. Movement disorders, in particular those arising in childhood, pose a diagnostic challenge. First, from a purely phenomenological point of view, the correct clinical classification of signs and symptoms may be difficult and require expert evaluation. This is because the clinical picture is often a mixture of hyperkinetic and hypokinetic disorders, and within hyperkinetic movement disorders, combined phenotypes are not unusual. Second, although several genes that cause movement disorders in children are now well-known, many of them have only been described in adult populations or discovered in patients after many years of disease. Furthermore, diseases that alter their mechanisms from childhood to adulthood are still little known, and many phenotypes in children are the result of a disruption of normal neurodevelopment. High-throughput gene screening addresses these difficulties and has modified the approach to genetic diagnosis. In the exome-sequencing era, customized genetic panels now offer the ability to perform fast and low-cost screening of the genes commonly involved in the pathogenesis of the disease. Here, we describe a 3-year study using a customized gene panel for pediatric-onset movement disorders in a selected cohort of children and adolescents. We report a satisfying diagnostic yield, further confirming the usefulness of gene panel analysis.

Defining the clinical-genetic and neuroradiological features in SPG54: description of eight additional cases and nine novel DDHD2 variants.

Recessive mutations in DDHD2 cause SPG54, a complex hereditary spastic paraplegia (HSP) with less than forty patients reported worldwide. In this retrospective, multicenter study we describe eight additional SPG54 cases harboring homozygous or compound heterozygous DDHD2 variants. Finally, we reviewed literature data on SPG54, with the aim to better define the phenotype and the brain magnetic resonance imaging (MRI) pattern as well as genotype-phenotype correlations. SPG54 is typically characterized by early-onset (i.e., congenital or, more frequently, infantile) delay in motor and cognitive milestones, coupled or followed by appearance of spasticity. Cognitive impairment is absent in adult-onset cases. Spasticity progresses over time. Abnormal eye movement, found in about 50% of cases, is the feature most frequently associated with spasticity and developmental delay. Cerebellar ataxia is a prominent sign in several patients, including one adult of this study, suggesting to include SPG54 in the differential diagnosis of spastic-ataxia syndromes. Brain MRI shows thin corpus callosum and non-specific periventricular white matter lesions in about 90% and 70% of cases, respectively. Brain MR spectroscopy reveals abnormal lipid peak in 90% of investigated patients. Twenty-one pathogenic changes have been reported so far, many of which are nonsense or small deletion/duplication. Most mutations appear to be private, with only two mutations recurring in three (i.e., R287*) or more families (i.e., D660H). The identification of nine novel variants expands the molecular spectrum of DDHD2-related HSP and corroborates the notion of a quite homogeneous clinical and neuroradiological phenotype in spite of different genotypes.

SLC2A1 mutations are a rare cause of pediatric-onset hereditary spastic paraplegia.

SLC2A1 mutations cause glucose transporter type 1 deficiency syndrome, whose phenotypic spectrum is a continuum, ranging from classic to variant phenotypes, the latter accounting for about 10% of cases. Very few SLC2A1-mutated patients with a spastic paraplegia phenotype have been reported so far, and they are associated with paroxysmal choreo-athetosis (i.e., DYT9). The authors describe two sporadic children with pure and complex hereditary spastic paraplegia (HSP) without paroxysmal non-epileptic movement disorders harboring heterozygous de novo SLC2A1 pathogenic variants. These patients have been identified by a targeted panel for HSP among 140 pediatric- and adult-onset unrelated cases with pure and complex HSP, thus indicating an overall prevalence of 1.4% of SLC2A1 mutations, which increases to 3% if only pediatric-onset patients are considered. The implications of these findings in the diagnostic work-up of HSP patients are discussed.

The impact of next-generation sequencing on the diagnosis of pediatric-onset hereditary spastic paraplegias: new genotype-phenotype correlations for rare HSP-related genes.

Hereditary spastic paraplegias (HSP) are clinical and genetic heterogeneous diseases with more than 80 disease genes identified thus far. Studies on large cohorts of HSP patients showed that, by means of current technologies, the percentage of genetically solved cases is close to 50%. Notably, the percentage of molecularly confirmed diagnoses decreases significantly in sporadic patients. To describe our diagnostic molecular genetic approach on patients with pediatric-onset pure and complex HSP, 47 subjects with HSP underwent molecular screening of 113 known and candidate disease genes by targeted capture and massively parallel sequencing. Negative cases were successively analyzed by multiplex ligation-dependent probe amplification (MLPA) analysis for the SPAST gene and high-resolution SNP array analysis for genome-wide CNV detection. Diagnosis was molecularly confirmed in 29 out of 47 (62%) patients, most of whom had clinical diagnosis of cHSP. Although SPG11 and SPG4 remain the most frequent cause of, respectively, complex and pure HSP, a large number of pathogenic variants were disclosed in POLR3A, FA2H, DDHD2, ATP2B4, ENTPD1, ERLIN2, CAPN1, ALS2, ADAR1, RNASEH2B, TUBB4A, ATL1, and KIF1A. In a subset of these disease genes, phenotypic expansion and novel genotype-phenotype correlations were recognized. Notably, SNP array analysis did not provide any significant contribution in increasing the diagnostic yield. Our findings document the high diagnostic yield of targeted sequencing for patients with pediatric-onset, complex, and pure HSP. MLPA for SPAST and SNP array should be limited to properly selected cases based on clinical suspicion.

Childhood Rapid-Onset Ataxia: Expanding the Phenotypic Spectrum of ATP1A3 Mutations.

ATP1A3 mutations are related to a wide spectrum of clinical conditions, including several defined syndromes as rapid-onset dystonia-parkinsonism (RDP), alternating hemiplegia of childhood (AHC), and cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural hearing loss (CAPOS), together with many other intermediate phenotypes. Ataxia is always more increasingly reported, either as accessory or prominent sign, in ATP1A3-related conditions, being thus considered as a peculiar feature of this spectrum. Here, we report three cases of childhood rapid-onset ataxia due to two different ATP1A3 variants. Interestingly, two patients (mother and son) showed a variant c.2266C>T (p.R756C), while the third carried the c.2452G>A (p.E818K) variant, commonly described in association with CAPOS syndrome. Our report contributes to extent the phenotypic spectrum of ATP1A3 mutations, remarking childhood rapid-onset ataxia as an additional clinical presentation of ATP1A3-related conditions. Finally, we discussed this phenomenology in the light of translational evidence from a RDP animal model.