常染色体显性小脑性共济失调致病基因动态突变位点三核苷酸重复变异的研究

目的 探讨毛细管电泳技术在动态突变位点检测中的技术问题,并分析常染色体显性小脑性共济失调(autosomal dominant cerebellar ataxias,ADCA)患者与正常对照人群脊髓小脑性共济失调(spinocerebellar ataxia,SCA)1,2,3,6,7亚型的致病基因动态突变位点三核苷酸重复数的分布范围,以期为今后标准化ADCA基因检测技术及中国人群制定相关基因动态突变量化标准提供依据.方法 以263个ADCA家系的先证者及261个无亲缘关系的正常对照为对象,应用荧光PCR-毛细管电泳及DNA测序技术进行上述SCA致病基因内动态突变位点基因分型,统计分析不同对照下各基因动态突变位点毛细管电泳检测重复数与DNA测序结果的差异,以及各基因三核苷酸重复特点及重复次数分布范围.结果 以DNA测序所确定的重复次数为标准,SCA各致病基因动态突变位点的PCR产物在毛细管电泳中,迁移率均大于GC含量相对均衡的分子量内标片段,其中SCA2、6、7亚型基因位点尤为明显.以各基因已知CAG重复数片段为外标计算受检标本CAG重复数,可将误差缩小至±1个拷贝.在各基因CAG正常重复范围内,PCR产物毛细管电泳迁移率主要与CAG拷贝数相关,而与CAG拷贝数变异所致PCR产物GC含量变化的关系不明显.在263个ADCA家系中,发现SCA1家系6个(2.28%),SCA2家系8个(3.04%),SCA3家系81个(30.80%),未发现SCA6和SCA7家系.排除上述突变基因后,正常等位基因重复次数变异范围在SCA1为17～36次,杂合率为76.1%,SCA2为13～30次,杂合率为17.7%,SCA3为14～39次,杂合率为74.4%,SCA6为6～16次,杂合率为72.1%,SCA7为6～13次,杂合率为41.3%.突变等位基因重复次数变化范围在SCA1为49～56次,SCA2为36～41次,SCA3为59～81次.未发现单一位点纯合突变或两位点双重杂合突变患者.结论 通过设置有限数量的已知拷贝数对照,进行荧光PCR-毛细管电泳检测,可以准确地计算出SCA致病基因动态突变位点CAG重复次数.本研究结果支持中国人群中SCA3致病基因突变是导致ADCA的最常见病因.SCA1,2,3,6,7亚型致病基因正常与突变的CAG重复数资料可为中国人ADCA动态突变量化标准的建立提供参考.     

Frequency analysis of autosomal dominant cerebellar ataxias in Japanese patients and clinical characterization of spinocerebellar ataxia type 6

Using a molecular diagnostic approach, we investigated 101 kindreds with autosomal dominant cerebellar ataxias (ADCAs) from the central Honshu island of Japan, including spinocerebellar ataxia type 1 (SCA1), spinocerebellar ataxia type 2 (SCA2), Machado–Joseph disease (MJD), dentatorubral and pallidoluysian atrophy (DRPLA) and spinocerebellar ataxia type 6 (SCA6). In our unselected series, MJD was the most common type of ADCA, accounting for 33.7% followed by DRPLA (19.8%), SCA2 (5.9%) and SCA6 (5.9%). No SCA1 mutations were identified. We analysed the clinical features of six molecular confirmed SCA6 kindreds: in each family, there was an expanded allele in the α1A-voltage dependent calcium channel comprising between 23 and 25 CAG repeats. The mean age at onset of symptoms was 43±13 years. The clinical features consisted predominantly of cerebellar ataxia, dysarthria and horizontal nystagmus, which was generally consistent with ADCA type 3. However several new clinical features were found in some patients: dramatic anticipation, rapid disease progression, severe ataxia associated with action tremor or action myoclonus, and very early onset, which are not described as the classical features of ADCA type 3.     

Early onset and slow progression of SCA28, a rare dominant ataxia in a large four-generation family with a novel AFG3L2 mutation

Autosomal dominantly inherited spinocerebellar ataxias (SCAs) are a heterogeneous group of neurodegenerative disorders primarily affecting the cerebellum. Genetically, 26 different loci have been identified so far, although the corresponding gene has not yet been determined for 10 of them. Recently, mutations in the ATPase family gene 3-like 2 gene were presented to cause SCA type 28. To define the frequency of SCA28 mutations, we performed molecular genetic analyses in 140 unrelated familial cases with ataxia. Among other variations, we found a novel missense mutation at an evolutionarily conserved amino-acid position using a single-strand conformation polymorphism approach, followed by DNA sequencing. This amino-acid exchange p.E700K was detected in a four-generation German family and was not observed in a survey of 400 chromosomes from healthy control individuals.     

Spectrum and prevalence of autosomal dominant spinocerebellar ataxia in Hokkaido,the northern island of Japan: a study of 113 Japanese families

Autosomal dominant cerebellar ataxia (ADCA) is a genetically heterogeneous group of neurodegenerative disorders. To shed further light on the clinical and genetic spectrum of ADCA in Japan, we conducted a study to determine the frequency of a new variety of different subtypes of SCAs among ADCA patients. This current study was carried out from April 1999 to December 2006 on the basis of patients with symptoms and signs of ADCA disorders. PCR and/or direct sequencing were evaluated in a total of 113 families. Among them, 35 families were found to have the mutation associated with SCA6, 30 with SCA3, 11 with SCA1, five with SCA2, five with DRPLA, and one with SCA14. We also detected the heterozygous −16C → T single nucleotide substitution within the puratrophin-1 gene responsible for 16q22.1-linked ADCA in ten families. In this study, unusual varieties of SCA, including 27, 13, 5, 7, 8, 12, 17, and 16 were not found. Of the 113 patients, 14% had as yet unidentified ADCA mutations. The present study validates the prevalence of genetically distinct ADCA subtypes based on ethnic origin and geographical variation, and shows that 16q-linked ADCA has strong hereditary effects in patients with ADCAs in Japan. Rehana Basri, Ichiro Yabe, and Hiroyuki Soma contributed equally to this work.     

A linkage disequilibrium at the candidate gene locus for 16q-linked autosomal dominant cerebellar ataxia type III in Japan

We previously mapped the gene responsible for autosomal dominant cerebellar ataxia (ADCA) type III to a 10.9-cM interval between D16S3089 and D16S515 on chromosome 16q. This region, however, was identical to the candidate locus of spinocerebellar ataxia type 4 (SCA4). In this study, we extended our research to refine the gene locus of the disease by applying linkage disequilibrium with 20 microsatellite DNA markers. With 9 markers flanked by D16S3031 and D16S3107, we found that the affected individuals in six families had a common haplotype on their disease chromosomes. Furthermore, linkage disequilibrium was demonstrated with 5 informative markers: D16S3019 (P = 0.013), D16S3067 (P = 0.008), D16S3141 (P = 0.011), D16S496 (P = 0.032), and D16S3107 (P = 0.000). These results indicate that the disease could have originated from a common ancestor harboring a mutation within a less than 3-cM region between D16S3043 and D16S3095. The founder alleles were also observed in other patients with ADCA type III unrelated to the six families. Received: October 25, 2000 / Accepted: January 5, 2001     

Somatic mosaicism of the CAG repeat expansion in spinocerebellar ataxia type 3/Machado-Joseph disease

An expanded and unstable CAG repeat in the coding region of the MJD1 gene is the mutation responsible for spinocerebellar ataxia 3/Machado-Joseph disease. In order to determine whether there was a higher degree of instability in affected regions, the size of the expanded CAG repeat was analyzed in different regions of the central nervous system, in two unrelated SCA3/MJD patients. The degree of somatic mosaicism was quantified and compared to that in a SCA1 patient. Instability of the expanded CAG repeat was observed in peripheral tissues as well as in CNS of the three patients, but there was no correlation between the degree of mosaicism and the selective vulnerability of CNS structures. As in the other diseases caused by expanded CAG repeats, a lower degree of mosaicism was found in the cerebellar cortex of both SCA1 and SCA3/MJD patients, probably reflecting specific properties of this structure. In SCA3/MJD, the degree of mosaicism seemed to correlate with age at death rather than with the size of the expanded CAG repeat. Finally, somatic instability was more pronounced in SCA1 than in SCA3/MJD patients. Hum Mutat 11:23–27, 1998. © 1998 Wiley-Liss, Inc.     

Refining the phenotype of the THG1L (p.Val55Ala mutation)‐related mitochondrial autosomal recessive congenital cerebellar ataxia

Roughly 40 genes have been linked to autosomal recessive (AR) ataxia syndromes. Of these, at least 10 encode gene products localizing to the mitochondrion. tRNA‐histidine guanylyltransferase 1 like (THG1L) localizes to the mitochondrion and catalyzes the 3′–5′ addition of guanine to the 5′‐end of tRNA‐histidine. Previously, three siblings with early onset cerebellar dysfunction, developmental delay, pyramidal signs, and cerebellar atrophy on brain magnetic resonance imaging (MRI) were reported to carry homozygous V55A mutations in THG1L. Fibroblasts derived from these individuals showed abnormal mitochondrial networks when subjected to obligatory oxidative phosphorylation. A carrier rate of 0.8%, but no THG1L V55A homozygotes, was found in a cohort of 3,232 unrelated Ashkenazi Jewish individuals, and no homozygotes were found in Exac or gnomAD. This variant is reported with an allelic frequency of 0.02% in Exac, and is not listed in gnomAD. A similar phenotype was recently reported for another, homozygous variant p.L294P was reported with a similar, but more severely affected phenotype [Shaheen et al. (2019); Genetics in Medicine 21: 545–552]. Here, we report two additional Ashkenazi Jewish patients, carrying the same homozygous V55A mutation. We present bioinformatic analyses of the V55A mutation demonstrating high conservation in metazoan species. We refine the clinical and radiological phenotype and discuss the uniqueness of the clinical course of this novel mitochondrial AR ataxia in comparison to the diverse molecular etiologies and clinical phenotypes of other known mitochondrial AR ataxias.     

Physical map and haplotype analysis of 16q-linked autosomal dominant cerebellar ataxia (ADCA) type III in Japan

 Autosomal dominant cerebellar ataxia (ADCA) is a group of heterogeneous neurodegenerative disorders. We previously mapped a gene locus for ADCA with pure cerebellar syndrome (ADCA type III) to a 3-cM region in chromosome 16q, and found a common haplotype among affected individuals. This region was exactly within the locus for another ADCA, spinocerebellar ataxia type 4 (SCA4). To identify the gene causing 16q-linked ADCA type III, we constructed a contig with 38 bacterial artificial chromosome clones between D16S3043 and D16S3095. The size of this contig was estimated to be 4.8 Mb. We found more than 500 nucleotide tandem repeats, including 9 CAG/CTG repeats in this candidate region, although none of the 94 tandem repeats analyzed were expanded in affected individuals. However, we found 11 new polymorphic markers, giving 22 markers spanning the candidate region. By typing these markers on eight Japanese families with ADCA type III, including two new families, we found that a common “founder” haplotype is seen in a more restricted 3.8-Mb region, spanning markers GGAA05 and D16S3095. We present here a newly refined critical interval of 16q-ADCA type III/SCA4. Data of 11 new DNA markers on 16q22.1 would also be useful for other research of genes mapped to this region. Received: June 25, 2002 / Accepted: November 22, 2002 Correspondence to:H. Mizusawa     

Genetic variation in APOB, PCSK9, and ANGPTL3 in carriers of pathogenic autosomal dominant hypercholesterolemic mutations with unexpected low LDL-Cl Levels

Autosomal Dominant Hypercholesterolemia (ADH) is caused by LDLR and APOB mutations. However, genetically diagnosed ADH patients do not always exhibit the expected hypercholesterolemic phenotype. Of 4,669 genetically diagnosed ADH patients, identified through the national identification screening program for ADH, 75 patients (1.6%) had LDL-cholesterol (LDL-C) levels below the 50th percentile for age and gender prior to lipid-lowering therapy. The genes encoding APOB, PCSK9, and ANGPTL3 were sequenced in these subjects to address whether monogenic dominant loss-of-function mutations underlie this paradoxical phenotype. APOB mutations, resulting in truncated APOB, were found in five (6.7%) probands, reducing LDL-C by 56%. Rare variants in PCSK9, and ANGPTL3 completely correcting the hypercholesterolemic phenotype were not found. The common variants p.N902N, c.3842+82T>A, p.D2312D, and p.E4181K in APOB, and c.1863+94A>G in PCSK9 were significantly more prevalent in our cohort compared to the general European population. Interestingly, 40% of our probands carried at least one minor allele for all four common APOB variants compared to 1.5% in the general European population. While we found a low prevalence of rare variants in our cohort, our data suggest that regions in proximity of the analyzed loci, and linked to specific common haplotypes, might harbor additional variants that correct an ADH phenotype.     

常染色体显性成人多囊肾病两家系PKD1、PKD2基因的突变鉴定

目的 鉴定两个常染色体显性成人多囊肾病家系的致病突变.方法 采用酚氯仿法提取家系成员及无亲缘关系的100名健康对照个体的外周血白细胞DNA,PCR扩增先证者致病基因PKD1、PKD2的所有外显子序列及其侧翼内含子剪切区域,直接测序确定DNA序列的变异.通过家系和正常对照的比较分析,对检测到的变异是否与疾病相关进行了初步探讨.结果 在两个家系中共检测到5个序列变异:PKD1:c.2469G＞A,PKD1:c.5014_5015 delAG,PKD1:c.10529C＞T,PKD2:c.568G＞A和PKD2:c.2020-1_2020 delAG.其中PKD1:c.2469G＞A和PKD2:c.2020-1_2020 delAG为新发现的变异.此外,检测到的移码突变和剪切突变未见于家系中健康成员及无亲缘关系的正常对照.结论 PKD1:c.5014_5015 delAG和PKD2:c.2020-1_2020 delAG分别为家系A和B的致病突变,且PKD2:c.2020-1_2020 delAG为先证者新发生的突变.     

Missense mutations in the extracellular domain of the human neural cell adhesion molecule L1 reduce neurite outgrowth of murine cerebellar neurons

Mutations in L1CAM, the gene encoding the transmembrane multifunctional neuronal adhesion molecule L1, are associated with neurodevelopmental disorders including X-linked hydrocephalus and mental retardation. Some amino acid substitutions in various extracellular domains of L1 are known to affect posttranslational processing of the protein or its homophilic and heterophilic interactions. It is largely unknown, however, how these mutations result in neurodevelopmental disturbances and whether the effects of mutations on neurodevelopment can be modeled in vitro. We stably expressed full-length human wild type L1 and the known pathogenic missense mutations I179S, R184W, Y194C, and C264Y in NIH-3T3 cells. L1 protein synthesis, glycosylation pattern, and subcellular localization were analyzed. Neurite outgrowth of primary murine cerebellar neurons was measured after 23 hrs of co-cultivation using transfected NIH-3T3 cells as substrate. Like wild type L1, L1 protein with I179S or Y194C mutations was localized on the surface of the transfected substrate cells, but this was not the case with R184W or C264Y mutations. All four mutations were associated with reduced stimulation of neurite outgrowth. Measurement of neurite outgrowth on transfected substrate cells may be a suitable model for studying neurodevelopmental disturbances.     

Spectrum of NOTCH3 mutations in Korean patients with clinically suspicious cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is caused by mutations in the NOTCH3 gene on chromosome 19. Previous studies showed that NOTCH3 contains mutational hotspots that can vary among individuals of different ethnic backgrounds. In this study, we investigated the spectrum of NOTCH3 mutations in Korean patients with CADASIL. We retrospectively analyzed 156 patients who underwent NOTCH3 gene testing for molecular diagnosis of CADASIL using Sanger sequencing with a tiered approach. First, we screened previously reported mutational hotspots (exons 2-6, 8, 11, 18, 19, and 22). If no mutation was detected and samples were available, we extended our analysis to additional exons (7, 9, 10, 14, 15, 20, 21, 23, and 25). In 45 of 156 patients (28.8%), 29 mutations and 16 novel variants of unknown significance (VUS) were identified. The p.R544C mutation in exon 11 of NOTCH3 was the most frequently observed mutation (n = 8), followed by p.R75P in exon 3 (n = 7), p.R332C in exon 6 (n = 3), p.R54C in exon 2 (n = 2), and p.R90C in exon 3 (n = 2). Among the VUS, p.R1175W in exon 22, p.S414C in exon 8, and p.N1207S in exon 22 were found in 5, 3, and 2 patients, respectively. Other mutations and VUS were observed in 1 patient each. Although this was not a prospective, nationwide cohort study, the results above suggested that the spectrum of NOTCH3 mutations might be different in Koreans than in individuals of Caucasian ethnicity. Therefore, further analysis of Koreans with CADASIL might be necessary to implement a Korean-specific mutation screening paradigm.     

Genetic heterogeneity of dominantly inherited olivopontocerebellar atrophy (OPCA) in the Japanese: Linkage study of two pedigrees and evidence for the disease locus on chromosome 12q (SCA2)

Summary We did a linkage study of 2 multigenerational pedigrees with dominant olivopontocerebellar atrophy (OPCA) other than SCA1, with chromosome 12q microsatellites. Multipoint linkage analysis led to the conclusion that the disease locus locates within the 6.2 cM interval between IGF1 and D12S84/D12S105. This result coincides with that of Cuban ataxia pedigrees designated as SCA2. Our study provides genetic evidence that dominant OPCA in the Japanese consists of at least two genetically different disorders: SCA1 and SCA2.     

The coding region of TP53INP2, a gene expressed in the developing nervous system, is not altered in a family with autosomal recessive non-progressive infantile ataxia on chromosome 20q11-q13.

The locus for autosomal recessive infantile cerebellar ataxia (CLA3 or SCAR6) has been mapped to chromosome 20q11-q13 in a single Norwegian pedigree. We identified a relatively uncharacterised mouse gene Tp53inp2, and showed that its human orthologue mapped within this candidate interval. Tp53inp2 appears to encode a mammalian-specific protein with homology to the two Tp53inp1 isoforms that respond to cellular stress and interact with p53. We show that Tp53inp2 expression is highly restricted during mouse embryogenesis, with strong expression in the developing brain and spinal cord, as well as in the sensory and motor neuron tracts of the peripheral nervous system. Given this expression pattern, the neurological phenotype of CLA3 and the chromosomal localisation of TP53INP2, we searched the coding region for mutations in samples from individuals from the CLA3 pedigree. Our failure to detect causative mutations suggests that alterations in the coding region of TP53INP2 are not responsible for ataxia in this family, although we cannot rule out changes in non-coding elements of this gene.     

Update of spectrum c.35delG and c.‐23+1G>A mutations on the GJB2 gene in individuals with autosomal recessive nonsyndromic hearing loss

Hearing loss (HL) is the most common birth defect and the most prevalent sensorineural condition worldwide. It is associated with more than 1,000 mutations in at least 90 genes. Mutations of the gap junction beta‐2 protein (GJB2) gene located in the nonsyndromic hearing loss and deafness (DFNB1) locus (chromosome 13q11‐12) are the main causes of autosomal recessive nonsyndromic hearing loss worldwide, but important differences exist between various populations. In the present article, two common mutations of the GJB2 gene are compared for ethnic‐specific allele frequency, their function, and their contribution to genetic HL in different populations. The results indicated that mutations of the GJB2 gene could have arisen during human migration. Updates on the spectrum of mutations clearly show that frequent mutations in the GJB2 gene are consistent with the founder mutation hypothesis.     

Mutation characterization of CFTR gene in 206 Northern Irish CF families: Thirty mutations,including two novel,account for ∼︁94% of CF chromosomes

A variety of mutation detection techniques, including restriction endonuclease digestion, allele specific oligonucleotides, and automated fluorescent sequencing, were used in the identification of 15 CFTR mutations representing 86.7% of CF chromosomes in 206 Northern Irish cystic fibrosis (CF) families. A systematic analysis of the 27 exons and intron/exon boundaries of the CFTR gene was performed using denaturing gradient gel electrophoresis (DGGE) in an attempt to characterise the 55 unknown CF mutations in 51 patients. Twenty different mutations were detected by DGGE on 30 chromosomes accounting for a further 7.3% of CF alleles. Fifteen of these mutations had not previously been found in Northern Ireland, and two are novel, M1I(G>T) and V562L. In total, 30 CFTR mutations account for 93.9% of the 412 Northern Irish CF chromosomes tested. The three major CF mutations in Northern Ireland are ▵F508, G551D, and R117H with respective frequencies of 68.0%, 5.1%, and 4.1%. The efficacy of the DGGE technique was proven by the detection of 77 out of 77 control variants from all the CFTR exons. DGGE is a highly efficient and sensitive method for mutation screening especially in large genes where the mutation spectrum is known to be heterogeneous. © 1996 Wiley-Liss, Inc.     

Novel mutations in exon 2 of MATN3 affect residues within the α–helices of the A‐domain and can result in the intracellular retention of mutant matrilin‐3

Multiple epiphyseal dysplasia (MED) is a clinically variable and genetically heterogeneous chondrodysplasia characterized by mild to moderate short stature and early onset osteoarthritis. Some forms of MED result from mutations in the gene encoding the cartilage structural protein matrilin‐3 (MATN3). The majority of MATN3 mutations affect conserved residues within the β‐sheet of the single A‐domain of matrilin‐3. These mutations cause the protein to misfold and prevent its secretion from the rER, both in vitro and in vivo. More recently a single mutation (p.Phe105Ser) has been identified within the α1‐helix of the A‐domain, but its affect on the structure and/or function of matrilin‐3 is unknown. In this paper we describe the characterization of two additional α‐helical mutations (p.Ala173Asp and p.Lys231Asn) and show that both p.Phe105Ser and pAla173Asp prevent the secretion of A‐domain in vitro. In contrast, p.Lys231Asn does not prevent the secretion of matrilin‐3 A‐domain, nor does it disrupt the structure of this domain or inhibit its binding to type II or type IX collagen. Therefore, despite extensive biochemical analysis the disease mechanism of p.Lys231Asn remains unresolved and care should be taken in counseling for these types of mutation in MATN3. © 2007 Wiley‐Liss, Inc.     

Specific knock‐down of tissue non‐specific alkaline phosphatase mRNA levels inhibits intracellular lipid accumulation in 3T3‐L1 and HepG2 cells

The use of non‐specific inhibitors of tissue non‐specific alkaline phosphatase (TNSALP) in pre‐adipocytes blocks intracellular lipid accumulation. TNSALP is also expressed in hepatocytes, which are known to accumulate lipid in a similar manner to pre‐adipocytes. The purpose of this study was to use specific silencing of TNSALP mRNA, using short interfering (si) RNA, to investigate the role of TNSALP in intracellular lipid accumulation in 3T3‐L1 and HepG2 cells. Cellular activity of TNSALP was measured using an automated colorimetric assay, and intracellular lipid accumulation was determined using the lipid‐specific dye, Oil Red O. Cells were transfected with siRNA directed against TNSALP mRNA, and expression of the TNSALP gene was determined at selected time points postinduction of lipid droplet formation. Expression of the TNSALP gene was inhibited by a maximum of 88 ± 1.9% (P < 0.005 vs. control) 11 days after initiation of lipid droplet formation in the 3T3‐L1 cells and 80 ± 8.9% (P < 0.05 vs. control) after 4 days in the HepG2 cells. This led to significant inhibition of both TNSALP activity and intracellular lipid accumulation in both cell lines. These data demonstrates that TNSALP plays an important role in the control of lipid droplet formation in both pre‐adipocyte and hepatocyte cell lines.