Childhood Rapid-Onset Ataxia: Expanding the Phenotypic Spectrum of <Emphasis Type="Italic">ATP1A3</Emphasis> 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.     

<Emphasis Type="Italic">SBF1</Emphasis> mutations associated with autosomal recessive axonal neuropathy with cranial nerve involvement

Biallelic mutations in the SBF1 gene have been identified in one family with demyelinating Charcot-Marie-Tooth disease (CMT4B3) and two families with axonal neuropathy and additional neurological and skeletal features. Here we describe novel sequence variants in SBF1 (c.1168C>G and c.2209_2210del) as the potential causative mutations in two siblings with severe axonal neuropathy, hearing loss, facial weakness and bulbar features. Pathogenicity of these variants is supported by co-segregation and in silico analyses and evolutionary conservation. Our findings suggest that SBF1 mutations may cause a syndromic form of autosomal recessive axonal neuropathy (AR-CMT2) in addition to CMT4B3.     

A novel <Emphasis Type="Italic">KCNA1</Emphasis> mutation in a family with episodic ataxia and malignant hyperthermia

Episodic ataxia type 1 (EA1) is an autosomal dominant channelopathy caused by mutations in KCNA1, which encodes the voltage-gated potassium channel, Kv1.1. Eleven members of an EA family were evaluated with molecular and functional studies. A novel c.746T>G (p.Phe249Cys) missense mutation of KCNA1 segregated in the family members with episodic ataxia, myokymia, and malignant hyperthermia susceptibility. No mutations were found in the known malignant hyperthermia genes RYR1 or CACNA1S. The Phe249Cys-Kv1.1 channels did not show any currents upon functional expression, confirming a pathogenic role of the mutation. Malignant hyperthermia may be a presentation of KCNA1 mutations, which has significant implications for the clinical care of these patients and illustrates the phenotypic heterogeneity of KCNA1 mutations.     

New <Emphasis Type="Italic">ATP8A2</Emphasis> gene mutations associated with a novel syndrome: encephalopathy,intellectual disability,severe hypotonia,chorea and optic atrophy

We report the clinical and biochemical findings from two unrelated patients who presented with a novel syndrome: encephalopathy, intellectual disability, severe hypotonia, chorea and optic atrophy. Whole exome sequencing (WES) uncovered a homozygous mutation in the ATP8A2 gene (NM_016529:c.1287G > T, p.K429N) in one patient and compound heterozygous mutations (c.1630G > C, p.A544P and c.1873C > T, p.R625W) in the other. Only one haploinsufficiency case and a family with a homozygous mutation in ATP8A2 gene (c.1128C > G, p.I376M) have been described so far, with phenotypes that differed slightly from the patients described herein. In conclusion, our data expand both the genetic and phenotypic spectrum associated with ATP8A2 gene mutations.     

Two novel heterozygous <Emphasis Type="Italic">HTRA1</Emphasis> mutations in two pedigrees with cerebral small vessel disease families

Heterozygous HTRA1 mutations, recently, have been reported as a cause of autosomal dominant hereditary cerebral small vessel disease (CSVD). We herein describe clinical and neuroimaging findings in two familial CSVD with two different heterozygous HTRA1 mutations. Detailed clinical and neuroimaging examination were conducted in probands and their available family members. A next-generation sequencing-based comprehensive gene panel was used to investigate their causative mutations. A novel heterozygous missense variant c.527T>C (p.V176A) and a novel heterozygous nonsense variant c.589C>T (p.R197X) in HTRA1 gene were detected in probands of family 1 and family 2, respectively. Co-segregation analysis in family 1 showed eight family members were mutation carriers. All alive male patients showed typical clinical and neuroimaging features of CSVD. All alive female mutation carriers were clinical or neuroimaging asymptomatic. Screening of HTRA1 should be considered in patients with familial CSVD. A male predominance may exist in patients with heterozygous HTRA1 mutations and need to be further investigated.     

X-linked hypomyelination with spondylometaphyseal dysplasia (H-SMD) associated with mutations in <Emphasis Type="Italic">AIFM1</Emphasis>

An X-linked condition characterized by the combination of hypomyelinating leukodystrophy and spondylometaphyseal dysplasia (H-SMD) has been observed in only four families, with linkage to Xq25-27, and recent genetic characterization in two families with a common AIFM1 mutation. In our study, 12 patients (6 families) with H-SMD were identified and underwent comprehensive assessment accompanied by whole-exome sequencing (WES). Pedigree analysis in all families was consistent with X-linked recessive inheritance. Presentation typically occurred between 12 and 36 months. In addition to the two disease-defining features of spondylometaphyseal dysplasia and hypomyelination on MRI, common clinical signs and symptoms included motor deterioration, spasticity, tremor, ataxia, dysarthria, cognitive defects, pulmonary hypertension, nystagmus, and vision loss due to retinopathy. The course of the disease was slowly progressive. All patients had maternally inherited or de novo mutations in or near exon 7 of AIFM1, within a region of 70 bp, including synonymous and intronic changes. AIFM1 mutations have previously been associated with neurologic presentations as varied as intellectual disability, hearing loss, neuropathy, and striatal necrosis, while AIFM1 mutations in this small region present with a distinct phenotype implicating bone. Analysis of cell lines derived from four patients identified significant reductions in AIFM1 mRNA and protein levels in osteoblasts. We hypothesize that AIFM1 functions in bone metabolism and myelination and is responsible for the unique phenotype in this condition.     

A novel mutation in <Emphasis Type="Italic">LAMC3</Emphasis> associated with generalized polymicrogyria of the cortex and epilepsy

Occipital cortical malformation is a rare neurodevelopmental disorder characterized by pachygyria and polymicrogyria of the occipital lobes as well as global developmental delays and seizures. This condition is due to biallelic, loss-of-function mutations in LAMC3 and has been reported in four unrelated families to date. We report an individual with global delays, seizures, and polymicrogyria that extends beyond the occipital lobes and includes the frontal, parietal, temporal, and occipital lobes. Next-generation sequencing identified a homozygous nonsense mutation in LAMC3: c.3190C>T (p.Gln1064*). This finding extends the cortical phenotype associated with LAMC3 mutations.     

<Emphasis Type="Italic">DAT1</Emphasis> and <Emphasis Type="Italic">DRD4</Emphasis> genes involved in key dimensions of adult ADHD

Attention-deficit hyperactivity disorder (ADHD) is a highly heritable neurodevelopmental disorder often persisting in adulthood. Genetic studies of ADHD mainly focused on the Dopamine Transporter (DAT1) and the Dopamine Receptor 4 (DRD4) genes. Nevertheless, polymorphisms of these genes explain only a small fraction of the assigned risk, suggesting that intermediate dimensions and environmental factors should also be considered. We investigated in 77 adult ADHD subjects compared to 474 controls, how polymorphisms within the genes coding for DAT1 (40-bp VNTR in 3′UTR), the Dopamine Receptor 2 (DRD2) (rs1799732) and DRD4 (48-bp VNTR in exon 3), may modulate the expression of the disorder. By genotyping DAT1, we detected a new 9.5R allele showing a deletion of 40 bp and also an insertion of 19 bp compared to the 10R allele. This novel allele was found to be significantly protective for ADHD (p < 0.0001). Another significant difference was found in the distribution of DRD4 48-bp VNTR 6R allele when comparing patients and controls (p = 0.0007). In addition significant results were also found for DAT1 9.5R allele, which was associated with impulsiveness (p = 1.98 × 10^?4) and trait anger scores (p = 7.66 × 10^?4). Moreover, impulsiveness scores were partly modulated by an interaction between the DRD4 48-bp VNTR 6R allele and childhood maltreatment (p = 0.01), however, this result did not resist correction for multiple comparisons. Altogether, our results show the putative involvement of DAT1 and DRD4 genes in the aetiology of ADHD with a main role in modulation of key dimensions of the disorder.     

<Emphasis Type="Italic">ADCY5</Emphasis>-related dyskinesia presenting as familial myoclonus-dystonia

We describe a family with an autosomal dominant familial dyskinesia resembling myoclonus-dystonia associated with a novel missense mutation in ADCY5, found through whole-exome sequencing. A tiered analytical approach was used to analyse whole-exome sequencing data from an affected grandmother-granddaughter pair. Whole-exome sequencing identified 18,000 shared variants, of which 46 were non-synonymous changes not present in a local cohort of control exomes (n = 422). Further filtering based on predicted splicing effect, minor allele frequency in the 1000 Genomes Project and on phylogenetic conservation yielded 13 candidate variants, of which the heterozygous missense mutation c.3086T>G, p. M1029R in ADCY5 most closely matched the observed phenotype. This report illustrates the utility of whole-exome sequencing in cases of undiagnosed movement disorders with clear autosomal dominant inheritance. Moreover, ADCY5 mutations should be considered in cases with apparent myoclonus-dystonia, particularly where SCGE mutations have been excluded. ADCY5-related dyskinesia may manifest variable expressivity within a single family, and affected individuals may be initially diagnosed with differing neurological phenotypes.     

<Emphasis Type="Italic">ARHGEF9</Emphasis> mutations in epileptic encephalopathy/intellectual disability: toward understanding the mechanism underlying phenotypic variation

ARHGEF9 resides on Xq11.1 and encodes collybistin, which is crucial in gephyrin clustering and GABA_A receptor localization. ARHGEF9 mutations have been identified in patients with heterogeneous phenotypes, including epilepsy of variable severity and intellectual disability. However, the mechanism underlying phenotype variation is unknown. Using next-generation sequencing, we identified a novel mutation, c.868C > T/p.R290C, which co-segregated with epileptic encephalopathy, and validated its association with epileptic encephalopathy. Further analysis revealed that all ARHGEF9 mutations were associated with intellectual disability, suggesting its critical role in psychomotor development. Three missense mutations in the PH domain were not associated with epilepsy, suggesting that the co-occurrence of epilepsy depends on the affected functional domains. Missense mutations with severe molecular alteration in the DH domain, or located in the DH-gephyrin binding region, or adjacent to the SH3-NL2 binding site were associated with severe epilepsy, implying that the clinical severity was potentially determined by alteration of molecular structure and location of mutations. Male patients with ARHGEF9 mutations presented more severe phenotypes than female patients, which suggests a gene-dose effect and supports the pathogenic role of ARHGEF9 mutations. This study highlights the role of molecular alteration in phenotype expression and facilitates evaluation of the pathogenicity of ARHGEF9 mutations in clinical practice.     

Coexistence of <Emphasis Type="Italic">CLCN1</Emphasis> and <Emphasis Type="Italic">SCN4A</Emphasis> mutations in one family suffering from myotonia

Non-dystrophic myotonias are characterized by clinical overlap making it challenging to establish genotype-phenotype correlations. We report clinical and electrophysiological findings in a girl and her father concomitantly harbouring single heterozygous mutations in SCN4A and CLCN1 genes. Functional characterization of N1297S hNav1.4 mutant was performed by patch clamp. The patients displayed a mild phenotype, mostly resembling a sodium channel myotonia. The CLCN1 c.501C>G (p.F167L) mutation has been already described in recessive pedigrees, whereas the SCN4A c.3890A>G (p.N1297S) variation is novel. Patch clamp experiments showed impairment of fast and slow inactivation of the mutated Nav1.4 sodium channel. The present findings suggest that analysis of both SCN4A and CLCN1 genes should be considered in myotonic patients with atypical clinical and neurophysiological features.     

The complete mitochondrial genome of <Emphasis Type="Italic">Ovis ammon darwini</Emphasis> (Artiodactyla: Bovidae)

Ovis ammon darwini: has been listed as a near-threatened species by IUCN-World Conservation Union due to over-hunting and poaching, competition with domestic livestock, and habitat destruction. Study on molecular biology research provides the scientific basis for the protection and sustainable utilization of key endangered species. Mitochondrial genome is very useful for researches in ecology, systematics and conservation biology. In this study, the complete mitochondrial genome sequence of O. a. darwini was determined by next-generation sequencing data, which is 16,618 bp in length and contains 13 protein-coding genes(PCGs), 2 rRNAs genes, 22 tRNAs genes and a non-coding control region. Base composition of genome is A(33.7?%), C(25.8?%), G(13.1?%), T(27.4?%) with an A?+?T content of 61.1?%. Phylogenetic analysis suggested that the systematic status of O. a. darwini was more closed related to O. a. hodgsoni clustered with O. ammon. The mitogenome of O. a. darwini offered significant information for molecular genetic research of O. ammon.     

Mutations in <Emphasis Type="Italic">dock1</Emphasis> disrupt early Schwann cell development

Background

In the peripheral nervous system (PNS), specialized glial cells called Schwann cells produce myelin, a lipid-rich insulating sheath that surrounds axons and promotes rapid action potential propagation. During development, Schwann cells must undergo extensive cytoskeletal rearrangements in order to become mature, myelinating Schwann cells. The intracellular mechanisms that drive Schwann cell development, myelination, and accompanying cell shape changes are poorly understood.

Methods

Through a forward genetic screen in zebrafish, we identified a mutation in the atypical guanine nucleotide exchange factor, dock1, that results in decreased myelination of peripheral axons. Rescue experiments and complementation tests with newly engineered alleles confirmed that mutations in dock1 cause defects in myelination of the PNS. Whole mount in situ hybridization, transmission electron microscopy, and live imaging were used to fully define mutant phenotypes.

Results

We show that Schwann cells in dock1 mutants can appropriately migrate and are not decreased in number, but exhibit delayed radial sorting and decreased myelination during early stages of development.

Conclusions

Together, our results demonstrate that mutations in dock1 result in defects in Schwann cell development and myelination. Specifically, loss of dock1 delays radial sorting and myelination of peripheral axons in zebrafish.

     

A Novel Homozygous Mutation in <Emphasis Type="Italic">SPTBN2</Emphasis> Leads to Spinocerebellar Ataxia in a Consanguineous Family: Report of a New Infantile-Onset Case and Brief Review of the Literature

The objective of this study was the identification of likely genes and mutations associated with an autosomal recessive (AR) rare spinocerebellar ataxia (SCA) phenotype in two patients with infantile onset, from a consanguineous family. Using genome-wide SNP screening, autozygosity mapping, targeted Sanger sequencing and nextgen sequencing, family segregation analysis, and comprehensive neuropanel, we discovered a novel mutation in SPTBN2. Next, we utilized multiple sequence alignment of amino acids from various species as well as crystal structures provided by protein data bank (PDB# 1WYQ and 1WJM) to model the mutation site and its effect on β-III-spectrin. Finally, we used various bioinformatic classifiers to determine pathogenicity of the missense variant. A comprehensive clinical and diagnostic workup including radiological exams were performed on the patients as part of routine patient care. The homozygous missense variant (c.1572C>T; p.R414C) detected in exon 2 was fully segregated in the family and absent in a large ethnic cohort as well as publicly available data sets. Our comprehensive targeted sequencing approaches did not reveal any other likely candidate variants or mutations in both patients. The two male siblings presented with delayed motor milestones and cognitive and learning disability. Brain MRI revealed isolated cerebellar atrophy more marked in midline inferior vermis at ages of 3 and 6.5 years. Sequence alignments of the amino acids for β-III-spectrin indicated that the arginine at 414 is highly conserved among various species and located towards the end of first spectrin repeat domain. Inclusive bioinformatic analysis predicted that the variant is to be damaging and disease causing. In addition to the novel mutation, a brief literature review of the previously reported mutations as well as clinical comparison of the cases were also presented. Our study reviews the previously reported SPTBN2 mutations and cases. Moreover, the novel mutation, p.R414C, adds up to the literature for the infantile-onset form of autosomal recessive ataxia associated with SPTBN2. Previously, few SPTBN2 recessive mutations have been reported in humans. Animal models especially the β-III^?/? mouse model provided insights into early coordination and gait deficit suggestive of loss-of-function. It is expected to see more recessive SPTBN2 mutations appearing in the literature during the upcoming years.     

Recurrent <Emphasis Type="Italic">KIF2A</Emphasis> mutations are responsible for classic lissencephaly

Kinesins play a critical role in the organization and dynamics of the microtubule cytoskeleton, making them central players in neuronal proliferation, neuronal migration, and postmigrational development. Recently, KIF2A mutations were identified in cortical malformation syndromes associated with microcephaly. Here, we detected two de novo p.Ser317Asn and p.His321Pro mutations in KIF2A in two patients with lissencephaly and microcephaly. In parallel, we re-evaluated the two previously reported cases showing de novo mutations of the same residues. The identification of mutations only in the residues Ser317 and His321 suggests these are hotspots for de novo mutations. Both mutations lead to a classic form of lissencephaly, with a posterior to anterior gradient, almost indistinguishable from LIS1-related lissencephaly. However, three fourths of patients also showed variable congenital and postnatal microcephaly, up to ?5 SD. Located in the motor domain of the KIF2A protein, the Ser317 and His321 alterations are expected to disrupt binding or hydrolysis of ATP and consequently the MT depolymerizing activity. This report also establishes that KIF2A mutations represent significant causes of classic lissencephaly with microcephaly.     

Very mild features of dysequilibrium syndrome associated with a novel <Emphasis Type="Italic">VLDLR</Emphasis> missense mutation

Dysequilibrium syndrome (DES) is a non-progressive congenital ataxia characterized by severe intellectual deficit, truncal ataxia and markedly delayed, quadrupedal or absent ambulation. Recessive loss-of-function mutations in the very low density lipoprotein receptor (VLDLR) gene represent the most common cause of DES. Only two families have been reported harbouring homozygous missense mutations, both with a similarly severe phenotype. We report an Italian girl with very mild DES caused by the novel homozygous VLDLR missense mutation p.(C419Y). This unusually benign phenotype possibly relates to a less disruptive effect of the mutation, falling within a domain (EGF-B) not predicted as crucial for the protein function.     

Novel Homozygous <Emphasis Type="Italic">KCNJ10</Emphasis> Mutation in a Patient with Non-syndromic Early-Onset Cerebellar Ataxia

Mutations in KCNJ10, which encodes the inwardly rectifying potassium channel Kir4.1, a primary regulator of membrane excitability and potassium homeostasis, cause a complex syndrome characterized by seizures, sensorineural deafness, ataxia, intellectual disability, and electrolyte imbalance called SeSAME/EAST syndrome. We describe a 41-year-old patient with non-syndromic, slowly progressive, early-onset ataxia. Targeted next-generation sequencing identified a novel c.180 T?>?G (p.Ile60Met) missense homozygous mutation. The mutated residue Ile60Met likely impairs phosphatidylinositol 4, 5-bisphosphate (PIP2) binding which is known to play an essential role in channel gating. Our study expands the clinical and mutational spectrum of KCNJ10-related disorders and suggests that screening of this gene should be implemented in patients with early-onset ataxia, with or without syndromic features.     

Novel mutations in <Emphasis Type="Italic">IBA57</Emphasis> are associated with leukodystrophy and variable clinical phenotypes

Defects of the Fe/S cluster biosynthesis represent a subgroup of diseases affecting the mitochondrial energy metabolism. In the last years, mutations in four genes (NFU1, BOLA3, ISCA2 and IBA57) have been related to a new group of multiple mitochondrial dysfunction syndromes characterized by lactic acidosis, hyperglycinemia, multiple defects of the respiratory chain complexes, and impairment of four lipoic acid-dependent enzymes: α-ketoglutarate dehydrogenase complex, pyruvic dehydrogenase, branched-chain α-keto acid dehydrogenase complex and the H protein of the glycine cleavage system. Few patients have been reported with mutations in IBA57 and with variable clinical phenotype. Herein, we describe four unrelated patients carrying novel mutations in IBA57. All patients presented with combined or isolated defect of complex I and II. Clinical features varied widely, ranging from fatal infantile onset of the disease to acute and severe psychomotor regression after the first year of life. Brain MRI was characterized by cavitating leukodystrophy. The identified mutations were never reported previously and all had a dramatic effect on IBA57 stability. Our study contributes to expand the array of the genotypic variation of IBA57 and delineates the leukodystrophic pattern of IBA57 deficient patients.     

<Emphasis Type="Italic">GNE</Emphasis> missense mutation in recessive familial amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a motor neuron disease eventually leading to death from respiratory failure. Recessive inheritance is very rare. Here, we describe the clinical findings in a consanguineous family with five men afflicted with recessive ALS and the identification of the homozygous mutation responsible for the disorder. The onset of the disease ranged from 12 to 35 years of age, with variable disease progressions. We performed clinical investigations including metabolic and paraneoplastic screening, cranial and cervical imaging, and electrophysiology. We mapped the disease gene to 9p21.1-p12 with a LOD score of 5.2 via linkage mapping using genotype data for single-nucleotide polymorphism markers and performed exome sequence analysis to identify the disease-causing gene variant. We also Sanger sequenced all coding sequences of SIGMAR1, a gene reported as responsible for juvenile ALS in a family. We did not find any mutation in SIGMAR1. Instead, we identified a novel homozygous missense mutation p.(His705Arg) in GNE which was predicted as damaging by online tools. GNE has been associated with inclusion body myopathy and is expressed in many tissues. We propose that the GNE mutation underlies the pathology in the family.