A novel frameshift variant in the CADASIL gene <Emphasis Type="Italic">NOTCH3</Emphasis>: pathogenic or not?

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy (CADASIL) represents the most common monogenic cause of adult-onset ischemic stroke and vascular dementia. It is caused by heterozygous missense mutations in the NOTCH3 gene, encoding a transmembrane receptor protein on vascular smooth muscle cells. Classical CADASIL mutations affect conserved cysteine residues of the Notch3 protein. By contrast, the role of non-canonical genetic variation in NOTCH3, in particular of variants causing a hypomorphic Notch3 protein, is subject to an ongoing scientific debate. In this context, we here report a novel NOTCH3 frameshift variant in exon 18 (NM_000435.2: c.2853_2857delTCCCG), causing a frameshift and introducing a premature stop codon, which was detected in a 43-year-old woman and her father. Both carriers of the variant were carefully evaluated, including serial follow-up in the index. Neither clinical nor imaging features provided convincing evidence for a classical CADASIL phenotype, thus reinforcing the concept of hypomorphic NOTCH3 variants most likely not being causative for CADASIL. Our finding, which is discussed in the light of the published literature, has practical implications for interpreting results of NOTCH3 molecular genetic testing as well as patient counseling.     

Parkinsonism in a pair of monozygotic CADASIL twins sharing the R1006C mutation: a transcranial sonography study

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), the most common hereditary cerebral small vessel disease, is caused by mutations in the NOTCH3 gene on chromosome 19. Clinical manifestations of CADASIL include recurrent transient ischemic attacks, strokes, cognitive defects, epilepsy, migraine and psychiatric symptoms. Parkinsonian features have variably been reported in CADASIL patients, but only a few patients showed a clear parkinsonian syndrome. We studied two patients, a pair of monozygotic twins, carrying the R1006C mutation of the NOTCH3 gene and affected by a parkinsonian syndrome. For the first time in CADASIL patients, we used transcranial sonography (TCS) to assess basal ganglia abnormalities. TCS showed a bilateral hyperechogenic pattern of substantia nigra in one twin, and a right hyperechogenic pattern in the other. In both patients, lenticular nuclei showed a bilateral hyperechogenic pattern, and the width of the third ventricle was slightly increased. The TCS pattern found in our CADASIL patients is characteristic neither for Parkinson’s disease, nor for vascular parkinsonism and seems to be specific and related to the disease-specific pathological features.     

CADASIL mutations and shRNA silencing of NOTCH3 affect actin organization in cultured vascular smooth muscle cells

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is the most common hereditary vascular dementia caused by mutations in NOTCH3 gene. Pathology is manifested in small- and middle-sized arteries throughout the body, though primarily in cerebral white matter. Hemodynamics is altered in CADASIL and NOTCH3 is suggested to regulate actin filament polymerization and thereby vascular tone. We analyzed NOTCH3 expression and morphology of actin cytoskeleton in genetically genuine cultured human CADASIL vascular smooth muscle cells (VSMCs) (including a cell line homozygous for p.Arg133Cys mutation) derived from different organs, and in control VSMCs with short hairpin RNA (shRNA)-silenced NOTCH3. NOTCH3 protein level was higher in VSMCs derived from adult than newborn arteries in both CADASIL and control VSMCs. CADASIL VSMCs showed altered actin cytoskeleton including increased branching and node formation, and more numerous and smaller adhesion sites than control VSMCs. Alterations in actin cytoskeleton in shRNA-silenced VSMCs were similar as in CADASIL VSMCs. Severity of the alterations in actin filaments corresponded to NOTCH3 expression level being most severe in VSMCs derived from adult cerebral arteries. These observations suggest that hypomorphic NOTCH3 activity causes alterations in actin organization in CADASIL. Furthermore, arteries from different organs have specific characteristics, which modify the effects of the NOTCH3 mutation and which is one explanation for the exceptional susceptibility of cerebral white matter arteries.     

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.     

伴皮质下梗死及白质脑病常染色体显性遗传性脑动脉病的NOTCH3基因诊断

目的 分析伴皮质下梗死及白质脑病常染色体显性遗传性脑动脉病((CADASIL)的NOTCH3基因突变类型.方法 对临床诊断为CADASIL的4例先证者、来自3个家系10例患者及4例无类似临床表现成员、以及100名健康对照者进行NOTCH3基因PCR扩增及变性高压液相色谱分析(DHPLC)检测;对DHPLC阳性结果进行DNA双向测序,明确致病性突变或多态类型.结果 在CADASIL先证者及其家系患者中共发现134半胱氨酸→酪氨酸(Cys134Tyr)、141精氨酸→半胱氨酸(Arg141Cys)、90精氨酸→半胱氨酸(Arg90Cys)3种突变类型,存在于第3、第4外显子,为杂合错义突变.同时发现15种多态类型.其中家系1和家系2中分别发现1名成员与先证者存在相同位点的NOTCH3基因致病性突变,尚未出现与先证者相应的临床表现,被确定为临床前期患者.结论 NOTCH3单基因突变是CADASIL的分子遗传学基础,第3、4外显子可能是中国CADASIL家系的热点突变区.第4外显子Cys134Tyr突变类型为国内首次报告.     

1例CADASIL家系的临床特征与基因突变分析

目的 分析1例皖江地区CADASIL家系的临床表现及基因突变特征.方法 随访记录1例CADASIL家系先证者的临床表现、实验室检查及影像学检查,对其NOTCH3基因突变热点区行基因检测.结果 先证者为1例53岁男性患者,病程中反复发作脑卒中并有家族发病史,另表现假性球麻痹、情绪障碍、冷漠和轻度认知功能障碍,无偏头痛史.其头颅核磁共振显示对称性双侧颞极及外囊区白质高信号病变.患者NOTCH3基因突变分析发现4号外显子区已知致病突变（c.580T〉C）和常见核苷酸多态性（rs1043994）.结论 c.580T〉C突变是中国人CADASIL病例首次报道,基因检测是确诊CADASIL的金标准.     

Cerebral Autosomal Dominant Arteriopathy With Subcortical Infarcts and Leukoencephalopathy Associated With a Novel In-Frame Mutation in the NOTCH3 Gene in a Japanese Patient

Here, we report a case involving a 67-year-old Japanese woman with cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) associated with a novel in-frame complex rearrangement in the NOTCH3 gene. The patient had gradually developed cognitive impairment since the occurrence of an ischemic stroke at the age of 53 years. Her mother had a history of stroke and dementia. Fluid-attenuated inversion recovery magnetic resonance imaging of the brain showed hyperintense lesions in the bilateral temporal poles, external capsules, and periventricular white matter accompanied by multiple cerebral microbleeds on T2*-weighted gradient-echo imaging. A novel in-frame mutation (c.598_610delinsAGAACCC) resulting in the loss of Cys201 in the fifth epidermal growth factor-like repeat of NOTCH3 was identified; this led to a diagnosis of CADASIL. In summary, we report a novel pathogenic mutation (NOTCH3 c.598_610delinsAGAACCC; p.Pro200_Ser204delinsArgThrPro) associated with CADASIL. Further investigations should elucidate the genotype-phenotype correlations in patients with this in-frame complex rearrangement.     

GBA-Associated Parkinson’s Disease and Other Synucleinopathies

Purpose of Review

GBA mutations are the most common known genetic cause of Parkinson’s disease (PD). Its biological pathway may be important in idiopathic PD, since activity of the enzyme encoded by GBA, glucocerebrosidase, is reduced even among PD patients without GBA mutations. This article describes the structure and function of GBA, reviews recent literature on the clinical phenotype of GBA PD, and suggests future directions for research, counseling, and treatment.

Recent Findings

Several longitudinal studies have shown that GBA PD has faster motor and cognitive progression than idiopathic PD and that this effect is dose dependent. New evidence suggests that GBA mutations may be important in multiple system atrophy. Further, new interventional studies focusing on GBA PD are described. These studies may increase the interest of PD patients and caregivers in genetic counseling.

Summary

GBA mutation status may help clinicians estimate PD progression, though mechanisms underlying GBA and synucleinopathy require further understanding.

     

Phosphate Transporters Expression in Patients with Primary Familial Brain Calcifications

Primary familial brain calcification (PFBC), formerly known as Fahr disease, is a rare neurological disorder characterized by extensive calcification deposits in the brain. So far, four genes have been reported with variations associated with PFBC, SLC20A2, PDGFβ, PDGFRβ, and XPR1. Using real-time qPCR, we analyzed the expression of three inorganic phosphate (Pi) transporters (SLC20A1, SLC20A2, and XPR1) in patients with PFBC. Our results showed a significant reduction (~40%) of SLC20A2 expression in the patients carrying mutation whereas no significant change was observed within the patients without known mutations. No difference was detected in SLC20A1 and XPR1 expression between the groups compared to control. The results suggest that mutations in SLC20A2 gene by itself play an import role by reducing its expression in blood of PFBC patients. At the same time, we could not demonstrate a direct co-regulation between the three Pi transporters at mRNA level, once their expression did not change among the groups.     

Three novel mutations in 20 patients with hereditary spastic paraparesis

Hereditary spastic paraparesis (HSP) constitutes both genetic and clinically heterogeneous group of upper motor neuron diseases. Half of the individuals with autosomal dominant (AD) HSP have mutations in SPAST, ATL1, and REEP1 genes. This study was conducted to elucidate the genetic etiology of patients with the pure type AD-HSP diagnosis. The patient group consisted of 23 individuals from 6 families in Turkey. In the first step of work, Sanger sequencing (SS) was performed in ATL1, SPAST, and REEP1 genes and the second phase whole-exome sequencing (WES) was performed following SS analysis for the patients with no detected mutations in these genes. The results of this study revealed that in ATL1, 6 patients have previously reported c.776C?>?A mutation and 6 patients have novel c.470 T?>?C mutation. In SPAST, 3 patients have novel c.1072G?>?C mutation and 2 patients have novel c.1099-1G?>?C mutation. WES was performed in three patients, who had no detected mutation in these genes with SS analysis. In this approach, as previously reported c.1859 T?>?C mutation in KIAA0196 was detected, and it was confirmed with the patient’s relatives by SS. In three of patients, no HSP-associated variant could be identified in SS and WES. With this study, the molecular genetic etiology in 20 of 23 (87%) individuals that were included in this study with the utilization of SS and WES was elucidated. Utilization of SS and WES methods have enabled the identification of genetic etiology of HSP further with appropriate genetic counseling that was provided to the patients.     

A novel gain-of-function mutation in the <Emphasis Type="Italic">ITPR1</Emphasis> suppressor domain causes spinocerebellar ataxia with altered Ca<Superscript>2+</Superscript> signal patterns

We report three affected members, a mother and her two children, of a non-consanguineous Irish family who presented with a suspected autosomal dominant spinocerebellar ataxia characterized by early motor delay, poor coordination, gait ataxia, and dysarthria. Whole exome sequencing identified a novel missense variant (c.106C>T; p.[Arg36Cys]) in the suppressor domain of type 1 inositol 1,4,5-trisphosphate receptor gene (ITPR1) as the cause of the disorder, resulting in a molecular diagnosis of spinocerebellar ataxia type 29. In the absence of grandparental DNA, microsatellite genotyping of healthy family members was used to confirm the de novo status of the ITPR1 variant in the affected mother, which supported pathogenicity. The Arg36Cys variant exhibited a significantly higher IP₃-binding affinity than wild-type (WT) ITPR1 and drastically changed the property of the intracellular Ca²⁺ signal from a transient to a sigmoidal pattern, supporting a gain-of-function disease mechanism. To date, ITPR1 mutation has been associated with a loss-of-function effect, likely due to reduced Ca²⁺ release. This is the first gain-of-function mechanism to be associated with ITPR1-related SCA29, providing novel insights into how enhanced Ca²⁺ release can also contribute to the pathogenesis of this neurological disorder.     

Characterization and genetic diagnosis of centronuclear myopathies in seven Chinese patients

Centronuclear myopathies (CNMs) are a group of clinically and genetically heterogeneous muscle disorders. Here, we report a cohort of seven CNM patients with their clinical, histological, and morphological features. In addition, using the next-generation sequencing (NGS) technique (5/7 patients), we identified small indels: intronic, exonic, and missense mutations in MTM1, DNM2, and RYR1 genes. Further genetic studies revealed skewed X-chromosome inactivation in two female patients carrying MTM1 mutations. Based on the results of genetic analysis, these seven patients were classified as (1) X-linked recessive myotubular myopathy (patients 1–3) with MTM1 mutations and mild phenotype, (2) the autosomal dominant CNM (patients 4–6) with DNM2 mutations, and (3) the autosomal recessive CNM (patient 7) with RYR1 mutations. In all patients, histological findings featured a high proportion of fibers with central nuclei. Radial arrangement of the sarcoplasmic strands was observed in DNM2-CNM and RYR1-CNM patients. Muscle magnetic resonance imaging (MRI) revealed a proximal pattern of involvement presented in both MTM1-CNM and RYR1-CNM patients. A distal pattern of involvement was present in DNM2-CNM patients. Our findings thereby identified a number of novel features that expand the reported clinicopathological phenotype of CNMs in China.     

A case of CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and lekoencephalopathy) with Notch 3 (Arg169Cys) mutation and typical granular osmiophilic materials in peripheral small arteries]

We report a 64-year-old Japanese woman with recurrent ischemic strokes and progressive dementia without any cardiovascular risk factors. Her first stroke was at 45 years old, and she has a family history of ischemic strokes compatible with an autosomal dominant trait. Marked leukoaraiosis and multiple lacunar infarcts were shown on brain MR images, and no atherosclerotic changes were observed in her extra- and intra-cranial arteries by cervical arterial echography and intracranial MR angiography. Excluded other inherited or metabolic diseases causing leukodystrophy by examination of her blood samples, her disease was diagnosed as CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and lekoencephalopathy). We demonstrated granular osmiophilic materials (GOM) on the wall of small arteries from a biopsied peripheral nerve tissue specimen and detected a mutation Arg169Cys of Notch 3 gene. Many CADASIL patients have been reported and over 28 kinds of mutations of the Notch 3 were identified in western countries, while few CADASIL patients have been reported in Japanese people. Among them, eleven CADASIL families have been reported and only five mutations (Arg133Cys, Cys174Phe, Arg213Lys, Arg90Cys and Arg141Cys) have been determined so far. The mutation of Notch 3 in our patient was determined as Arg169Cys, and this is the first report on a Japanese patient with CADASIL due to this mutation.     

Charcot–Marie–Tooth disease: genetic subtypes in the Sardinian population

Charcot–Marie–Tooth disease (CMT) is characterised by great variability of genetic subtypes. This study aimed to assess the genetic subtypes of CMT disease in the Sardinian population. Genetic screening was performed for CMT cases (CMT1, CMT2, and hereditary neuropathy with susceptibility to pressure palsies [HNPP]). A total of 1,043 subjects (119 index cases) were evaluated. In CMT1 index cases (69/119; 58%), PMP22 duplication at 17p11.2 was the most frequent genetic diagnosis (60/69; 87%), followed by mutations in the GJB1 gene (5/69; 7.2%), in the SH3TC2 gene (3/69; 4.4%) and PMP22 Gly107Val point mutation (1/69; 1.4%). The CMT2 group (24/119; 20.1%) comprised 10/24 (41.6%) patients carrying MPZ gene Ser44Phe mutation, 6/24 (25%) with mutations in MFN2 and HSPB1, and 1/24 (4.2%) in GJB1 and LRSAM1. In the HNPP group (26/119; 21.9%), the majority of patients reported the PMP22 deletion (25/26; 96.2%). Further studies are needed to comprehend the overall picture of the disease in Mediterranean area.     

<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.     

Homozygous mutation,p.Pro304His,in IDH3A,encoding isocitrate dehydrogenase subunit is associated with severe encephalopathy in infancy

Mitochondrial encephalopathies are a heterogeneous group of disorders which generally carries a grave prognosis. Using exome sequencing, we identified a homozygous mutation, Pro-304-His in the IDH3A gene, in a patient suffering from infantile encephalopathy with peripheral and autonomic nervous system involvement. Mammalian isocitrate dehydrogenase (IDH) 3 is a heterotetramer of 2alfa, 1beta, and 1gamma subunits, and IDH3A encodes the alfa subunit of the mitochondrial NAD⁺-dependent IDH. Here we show that in contrast to wild-type human IDH3A, the human IDH3A which harbor the p.Pro304His mutation does not complement the yeast Δidh1/Δidh2 growth defect on ethanol-acetate. We therefore propose that homozygosity for the p.Pro304His mutation is deleterious for mitochondrial NAD⁺-specific IDH3A activity in human. IDH3A now joins the list of TCA cycle-related proteins, which includes ACO2, DLD, SLC25A19, FH, and succinate dehydrogenase subunits, all associated with neurological disorders.     

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.     

First large genomic inversion in familial cerebral cavernous malformation identified by whole genome sequencing

Familial cerebral cavernous malformations (CCMs) predispose to seizures and hemorrhagic stroke. Molecular genetic analyses of CCM1, CCM2, and CCM3 result in a mutation detection rate of up to 98%. However, only whole genome sequencing (WGS) in combination with the Manta algorithm for analyses of structural variants revealed a heterozygous 24 kB inversion including exon 1 of CCM2 in a 12-year-old boy with familial CCMs. Its breakpoints were fine-mapped, and quantitative analysis on RNA confirmed reduced CCM2 expression. Our data expand the spectrum of CCM mutations and indicate that the existence of a fourth CCM disease gene is rather unlikely.     

Epidermal growth factor receptor overexpression is common and not correlated to gene copy number in ependymoma

Purpose

The aim of this study was to investigate the epidermal growth factor receptor (EGFR) status in ependymoma specimens, as there is a need for new prognostic and druggable targets in this disease.

Methods

Ependymomas (WHO grade II, n = 40; WHO grade III, n = 15) located spinal (n = 35), infratentorial (n = 14), and supratentorial (n = 6) of 53 patients with a median age of 40 (range, 2–79) years were analyzed for Ki-67, p53, and EGFR expression by immunohistochemistry using a tissue microarray and for EGFR gene copy number alterations/mutations. Results were correlated to clinical data.

Results

EGFR overexpression was found in 30/60 % of ependymomas depending on the antibody used and was more pronounced in WHO grade III. High EGFR gene copy number gains were found in 6 (11 %) ependymomas with half of them being amplifications. EGFR amplified ependymomas displayed an EGFR overexpression with both antibodies in two of three cases. A missense mutation in exon 20 of EGFR (S768I) was detected in one amplified case.

Conclusions

EGFR is frequently overexpressed in ependymomas. Other mechanisms than amplification of the EGFR gene appear to contribute to EGFR overexpression in most cases. EGFR mutations may be present in a small subset of ependymomas.