Genetic and clinical landscape of childhood cerebellar hypoplasia and atrophy.

PURPOSE: Cerebellar hypoplasia and atrophy (CBHA) in children is an extremely heterogeneous group of disorders, but few comprehensive genetic studies have been reported. Comprehensive genetic analysis of CBHA patients may help differentiating atrophy and hypoplasia and potentially improve their prognostic aspects. METHODS: Patients with CBHA in 176 families were genetically examined using exome sequencing. Patients with disease-causing variants were clinically evaluated. RESULTS: Disease-causing variants were identified in 96 of the 176 families (54.5%). After excluding 6 families, 48 patients from 42 families were categorized as having syndromic associations with CBHA, whereas the remaining 51 patients from 48 families had isolated CBHA. In 51 patients, 26 aberrant genes were identified, of which, 20 (76.9%) caused disease in 1 family each. The most prevalent genes were CACNA1A, ITPR1, and KIF1A. Of the 26 aberrant genes, 21 and 1 were functionally annotated to atrophy and hypoplasia, respectively. CBHA+S was more clinically severe than CBHA-S. Notably, ARG1 and FOLR1 variants were identified in 2 families, leading to medical treatments. CONCLUSION: A wide genetic and clinical diversity of CBHA was revealed through exome sequencing in this cohort, which highlights the importance of comprehensive genetic analyses. Furthermore, molecular-based treatment was available for 2 families.

A reverse genetics and genomics approach to gene paralog function and disease: Myokymia and the juxtaparanode.

The leucine-rich glioma-inactivated (LGI) family consists of four highly conserved paralogous genes, LGI1-4, that are highly expressed in mammalian central and/or peripheral nervous systems. LGI1 antibodies are detected in subjects with autoimmune limbic encephalitis and peripheral nerve hyperexcitability syndromes (PNHSs) such as Isaacs and Morvan syndromes. Pathogenic variations of LGI1 and LGI4 are associated with neurological disorders as disease traits including familial temporal lobe epilepsy and neurogenic arthrogryposis multiplex congenita 1 with myelin defects, respectively. No human disease has been reported associated with either LGI2 or LGI3. We implemented exome sequencing and family-based genomics to identify individuals with deleterious variants in LGI3 and utilized GeneMatcher to connect practitioners and researchers worldwide to investigate the clinical and electrophysiological phenotype in affected subjects. We also generated Lgi3-null mice and performed peripheral nerve dissection and immunohistochemistry to examine the juxtaparanode LGI3 microarchitecture. As a result, we identified 16 individuals from eight unrelated families with loss-of-function (LoF) bi-allelic variants in LGI3. Deep phenotypic characterization showed LGI3 LoF causes a potentially clinically recognizable PNHS trait characterized by global developmental delay, intellectual disability, distal deformities with diminished reflexes, visible facial myokymia, and distinctive electromyographic features suggestive of motor nerve instability. Lgi3-null mice showed reduced and mis-localized Kv1 channel complexes in myelinated peripheral axons. Our data demonstrate bi-allelic LoF variants in LGI3 cause a clinically distinguishable disease trait of PNHS, most likely caused by disturbed Kv1 channel distribution in the absence of LGI3.

De novo variants in RHOBTB2, an atypical Rho GTPase gene, cause epileptic encephalopathy.

By whole exome sequencing, we identified three de novo RHOBTB2 variants in three patients with epileptic encephalopathies (EEs). Interestingly, all three patients showed acute encephalopathy (febrile status epilepticus), with magnetic resonance imaging revealing hemisphere swelling or reduced diffusion in various brain regions. RHOBTB2 encodes Rho-related BTB domain-containing protein 2, an atypical Rho GTPase that is a substrate-specific adaptor or itself is a substrate for the Cullin-3 (CUL3)-based ubiquitin ligase complex. Transient expression experiments in Neuro-2a cells revealed that mutant RHOBTB2 was more abundant than wild-type RHOBTB2. Coexpression of CUL3 with RHOBTB2 decreased the level of wild-type RHOBTB2 but not the level of any of the three mutants, indicating impaired CUL3 complex-dependent degradation of the three mutants. These data indicate that RHOBTB2 variants are a rare genetic cause of EEs, in which acute encephalopathy might be a characteristic feature, and that precise regulation of RHOBTB2 levels is essential for normal brain function.

De novo variants in CAMK2A and CAMK2B cause neurodevelopmental disorders.

Objective: α (CAMK2A) and ß (CAMK2B) isoforms of Calcium/calmodulin-dependent protein kinase II (CaMKII) play a pivotal role in neuronal plasticity and in learning and memory processes in the brain. Here, we explore the possible involvement of α- and ß-CaMKII variants in neurodevelopmental disorders. Methods: Whole-exome sequencing was performed for 976 individuals with intellectual disability, developmental delay, and epilepsy. The effect of CAMK2A and CAMK2B variants on CaMKII structure and firing of neurons was evaluated by computational structural analysis, immunoblotting, and electrophysiological analysis. Results: We identified a total of five de novo CAMK2A and CAMK2B variants in three and two individuals, respectively. Seizures were common to three individuals with CAMK2A variants. Using a minigene splicing assay, we demonstrated that a splice site variant caused skipping of exon 11 leading to an in-frame deletion of the regulatory segment of CaMKII α. By structural analysis, four missense variants are predicted to impair the interaction between the kinase domain and the regulatory segment responsible for the autoinhibition of its kinase activity. The Thr286/Thr287 phosphorylation as a result of release from autoinhibition was increased in three mutants when the mutants were stably expressed in Neuro-2a neuroblastoma cells. Expression of a CaMKII α mutant in primary hippocampal neurons significantly increased A-type K+ currents, which facilitated spike repolarization of single action potentials. Interpretation: Our data highlight the importance of CaMKII α and CaMKII ß and their autoinhibitory regulation in human brain function, and suggest the enhancement of A-type K+ currents as a possible pathophysiological basis.

Clinical and molecular genetic characterization of two siblings with trisomy 2p24.3-pter and monosomy 5p14.3-pter.

Partial trisomy 2p syndrome is occasionally associated with neural tube defects (NTDs), such as anencephaly, encephalocele, and spina bifida, in addition to common features of intellectual disability, developmental delay, and characteristic facial appearance. The 2p24 region has been reported to be associated with NTDs. Here, we report the cases of 2 siblings with trisomy 2p24.3-pter and monosomy 5p14.3-pter caused by the paternal translocation t(2;5)(p24.3;p14.3). Of the two siblings, the elder sister had spina bifida. We determined the nucleotide sequences of the chromosomal breakpoints and found that the sizes of trisomy 2p and monosomy 5p segments were 18.77 and 17.89 Mb, respectively. NTDs were present in four of seven previously reported patients with trisomy 2p and monosomy 5p as well as in one of the two patients examined in the present study. Although the monosomy 5p of the nine patients were similar in size, the two patients reported here had the smallest size of trisomy 2p. When the clinical features of the nine patients were compared to the present two patients, the elder sister had postaxial polydactyly of the left foot in addition to the characteristic facial appearance and spina bifida, indicating that these features were associated with trisomy 2p24.3-pter. To our knowledge, this is the first study on spina bifida to determine the nucleotide sequences of breakpoints for trisomy 2p24.3-pter and monosomy 5p14.3-pter. Increased gene dosages of dosage-sensitive genes or genes at the trisomy segment (2p24.3) of the presented patients could be associated with NTDs of patients with trisomy 2p.

A case report of mitochondrial respiratory chain disorder in the neonatal period for which home mechanical ventilation was introduced.

We report the case of a patient born with extreme muscle hypotonia, respiratory failure, and slightly elevated serum levels of lactic acid. Histochemical examination and mitochondrial respiratory chain enzyme activities of a muscle biopsy specimen revealed reduced activities of complexes Ⅰ, Ⅲ, and Ⅳ, diagnostic of mitochondrial respiratory chain disorder. Hypertrophic cardiomyopathy developed as a complication and additional therapy was administered at 3 months after birth. He was able to be discharged to home on applied home mechanical ventilation with tracheotomy at 1 year old. The patient survived until 4 years and 10 months of age, upon which he died of bronchitis. Early-onset mitochondrial respiratory chain disorder shows very poor prognosis and long-term survival has not been reported. Prompt assessment of mitochondrial respiratory chain enzyme activities is necessary for the diagnosis of congenital nonspecific multiple-organ failure, and early intervention may achieve better prognosis for mitochondrial respiratory chain disorder.

Clinical, biochemical and metabolic characterisation of a mild form of human short-chain enoyl-CoA hydratase deficiency: significance of increased N-acetyl-S-(2-carboxypropyl)cysteine excretion.

BACKGROUND: Short-chain enoyl-CoA hydratase-ECHS1-catalyses many metabolic pathways, including mitochondrial short-chain fatty acid ß-oxidation and branched-chain amino acid catabolic pathways; however, the metabolic products essential for the diagnosis of ECHS1 deficiency have not yet been determined. The objective of this report is to characterise ECHS1 and a mild form of its deficiency biochemically, and to determine the candidate metabolic product that can be efficiently used for neonatal diagnosis. METHODS: We conducted a detailed clinical, molecular genetics, biochemical and metabolic analysis of sibling patients with ECHS1 deficiency. Moreover, we purified human ECHS1, and determined the substrate specificity of ECHS1 for five substrates via different metabolic pathways. RESULTS: Human ECHS1 catalyses the hydration of five substrates via different metabolic pathways, with the highest specificity for crotonyl-CoA and the lowest specificity for tiglyl-CoA. The patients had relatively high (∼7%) residual ECHS1 enzyme activity for crotonyl-CoA and methacrylyl-CoA caused by the compound heterozygous mutations (c.176A>G, (p.N59S) and c.413C>T, (p.A138V)) with normal mitochondrial complex I-IV activities. Affected patients excrete large amounts of N-acetyl-S-(2-carboxypropyl)cysteine, a metabolite of methacrylyl-CoA. CONCLUSIONS: Laboratory data and clinical features demonstrated that the patients have a mild form of ECHS1 deficiency harbouring defective valine catabolic and ß-oxidation pathways. N-Acetyl-S-(2-carboxypropyl) cysteine level was markedly high in the urine of the patients, and therefore, N-acetyl-S-(2-carboxypropyl)cysteine was regarded as a candidate metabolite for the diagnosis of ECHS1 deficiency. This metabolite is not part of current routine metabolic screening protocols, and its inclusion, therefore, holds immense potential in accurate diagnosis.

[Cervical myelopathy associated with os odontoideum after botulinum toxin treatment in a patient with cerebral palsy].

Os odontoideum is a separate ossicle from the odontoid process from the body of the axis by a variable transverse gap. A boy with cerebral palsy probably due to prematurity and kernicterus, was treated with botulinum toxin for continuous dystonic movements at the age of 3.5 years. Although botulinum toxin appeared to be remarkably effective for relaxing hypertonia, abnormal frequent anterior flexion of the neck remained. Because of feeding difficulty and frequent aspiration episodes, additional botulinum toxin therapy was discontinued. His condition seemed to be stable and he could walk with support at age 7. However, at age 8, he presented with decreased movement of the extremities and bilateral ankle clonus. Radiographic examination of the cervical spine revealed cystic lesion and os odontoideum. With cervical posterior fixation, the patient made a good recovery. Although athetoid cerebral palsy displays an increased risk of cervical myelopathy, os odontoideum is rare in early childhood. The frequent dynamic stress of the neck due to an unbalanced, persistently contracted state and sudden collapse, possibly attributed to botulinum toxin therapy, might have led to atlantoaxial instability and os odontoideum.

Genotype-phenotype correlations in alternating hemiplegia of childhood.

OBJECTIVE: Clinical severity of alternating hemiplegia of childhood (AHC) is extremely variable. To investigate genotype-phenotype correlations in AHC, we analyzed the clinical information and ATP1A3 mutations in patients with AHC. METHODS: Thirty-five Japanese patients who were clinically diagnosed with AHC participated in this study. ATP1A3 mutations were analyzed using Sanger sequencing. Detailed clinical information was collected from family members of patients with AHC and clinicians responsible for their care. RESULTS: Gene analysis revealed 33 patients with de novo heterozygous missense mutations of ATP1A3: Glu815Lys in 12 cases (36%), Asp801Asn in 10 cases (30%), and other missense mutations in 11 cases. Clinical information was compared among the Glu815Lys, Asp801Asn, and other mutation groups. Statistical analysis revealed significant differences in the history of neonatal onset, gross motor level, status epilepticus, and respiratory paralysis in the Glu815Lys group compared with the other groups. In addition, 8 patients who did not receive flunarizine had severe motor deteriorations. CONCLUSIONS: The Glu815Lys genotype appears to be associated with the most severe AHC phenotype. Although AHC is not generally seen as a progressive disorder, it should be considered a disorder that deteriorates abruptly or in a stepwise fashion, particularly in patients with the Glu815Lys mutation.

Phenotypic spectrum of COL4A1 mutations: porencephaly to schizencephaly.

OBJECTIVE: Recently, COL4A1 mutations have been reported in porencephaly and other cerebral vascular diseases, often associated with ocular, renal, and muscular features. In this study, we aimed to clarify the phenotypic spectrum and incidence of COL4A1 mutations. METHODS: We screened for COL4A1 mutations in 61 patients with porencephaly and 10 patients with schizencephaly, which may be similarly caused by disturbed vascular supply leading to cerebral degeneration, but can be distinguished depending on time of insult. RESULTS: COL4A1 mutations were identified in 15 patients (21%, 10 mutations in porencephaly and 5 mutations in schizencephaly), who showed a variety of associated findings, including intracranial calcification, focal cortical dysplasia, pontocerebellar atrophy, ocular abnormalities, myopathy, elevated serum creatine kinase levels, and hemolytic anemia. Mutations include 10 missense, a nonsense, a frameshift, and 3 splice site mutations. Five mutations were confirmed as de novo events. One mutation was cosegregated with familial porencephaly, and 2 mutations were inherited from asymptomatic parents. Aberrant splicing was demonstrated by reverse transcriptase polymerase chain reaction analyses in 2 patients with splice site mutations. INTERPRETATION: Our study first confirmed that COL4A1 mutations are associated with schizencephaly and hemolytic anemia. Based on the finding that COL4A1 mutations were frequent in patients with porencephaly and schizencephaly, genetic testing for COL4A1 should be considered for children with these conditions.

Spontaneous movements in the supine position of healthy term infants and preterm infants with or without periventricular leukomalacia.

AIM: The individual motor elements presumed to be essential for motor development were determined from spontaneous movements involving the entire body of normal term and preterm infants. Then, diagnostic items for motor abnormality in infants with periventricular leukomalacia (PVL) were investigated. METHODS: Video recordings of 24 healthy term infants, 21 normal preterm infants (8 males, 13 females; median gestational age 30 weeks; median birth weight 1216g) and 14 preterm infants with PVL (6 males, 8 females; median gestational age 30 weeks; median birth weight 1360g) were analyzed. RESULTS: In healthy term infants, predominant shoulder rotation was noticed until 1 month of age. After 2 months of age, isolated movements of the shoulder, elbow, hip, knee, and ankle frequently emerged. In preterm infants with PVL at the corrected age of 2 months, startle response and predominant shoulder rotation were more frequently seen and isolated neck, shoulder, elbow, hip, knee, and ankle movements were less frequently seen than in the normal preterm infants (Fisher's exact test, p<0.025). INTERPRETATION: At 2 months of age, isolated movements evolve, and their failure to occur is suggested to be a useful sign for the diagnosis of cerebral motor disorders.

De novo and inherited mutations in COL4A2, encoding the type IV collagen α2 chain cause porencephaly.

Porencephaly is a neurological disorder characterized by fluid-filled cysts or cavities in the brain that often cause hemiplegia. It has been suggested that porencephalic cavities result from focal cerebral degeneration involving hemorrhages. De novo or inherited heterozygous mutations in COL4A1, which encodes the type IV α1 collagen chain that is essential for structural integrity for vascular basement membranes, have been reported in individuals with porencephaly. Most mutations occurred at conserved Gly residues in the Gly-Xaa-Yaa repeats of the triple-helical domain, leading to alterations of the α1α1α2 heterotrimers. Here we report on two individuals with porencephaly caused by a heterozygous missense mutation in COL4A2, which encodes the type IV α2 collagen chain. Mutations c.3455G>A and c.3110G>A, one in each of the individuals, cause Gly residues in the Gly-Xaa-Yaa repeat to be substituted as p.Gly1152Asp and p.Gly1037Glu, respectively, probably resulting in alterations of the α1α1α2 heterotrimers. The c.3455G>A mutation was found in the proband's mother, who showed very mild monoparesis of the left upper extremity, and the maternal elder uncle, who had congenital hemiplegia. The maternal grandfather harboring the mutation is asymptomatic. The c.3110G>A mutation occurred de novo. Our study confirmed that abnormalities of the α1α1α2 heterotrimers of type IV collagen cause porencephaly and stresses the importance of screening for COL4A2 as well as for COL4A1.

Neonatal MRI in preterm infants with periventricular leukomalacia and mild disability.

BACKGROUND: The aim of the present study was to describe the neonatal magnetic resonance imaging (MRI) findings of preterm infants with periventricular leukomalacia and mild neurological disability. METHODS: MRI findings at term equivalent were retrospectively investigated in eight preterm infants with mild disability and periventricular leukomalacia diagnosed on MRI in infancy. RESULTS: Linear, spotted, or macular areas of hyperintensity on T1-weighted imaging and hypointensity on T2-weighted imaging were identified in all subjects in the white matter lateral to the body of the lateral ventricle. No cystic lesions were seen. These findings were more widespread and more clearly visualized on T2-weighted imaging than T1-weighted imaging. CONCLUSIONS: Linear, spotted, or macular lesions that are hyperintense on T1-weighted imaging and hypointense on T2-weighted imaging are possibly compatible with periventricular leukomalacia.