Analysis of chromosome 5q13 genes in amyotrophic lateral sclerosis: Homozygous naip deletion in a sporadic case

Although defects in the gene encoding the enzyme cytosolic copperlzinc superoxide dismutase (SODI) have been reported in 20% of familial amyotrophic lateral sclerosis (ALS) patients, the etiology of the remaining familial cases and the more common sporadic form of the disease remains unknown. Recently, deletions of the neuronal apoptosis inhibitory protein gene NAZP, of the survival motor neuron gene SMN, and of a further cDNA fragment, XS2G3, have been reported in childhood7-onset proximal spinal muscular atrophy (SMA), another disorder with pathology restricted to the motor system. We have therefore investigated the possibility of alterations in SMN and NAIP in 154 patients with ALS (135 sporadic cases, 17 familial cases). None of these patients revealed mutations in SMN by single-strand conformation polymorphism analysis. A single patient revealed a partial deletion of NAIP, with a homozygous absence of NAIP exon 5. While it is possible that this individual is one of the rare carriers of SMA who show NAIP deletions, a further explanation is that the NAIP deletion is in some way contributing to the ALS phenotype in this individual.     

Association between centromeric deletions of the SMN gene and sporadic adult-onset lower motor neuron disease

The telomeric copy (t) of the survival motor neuron (SMN) gene is homozygously deleted in more than 90% of patients with infantile motor neuron disease (MND). In the general population, no homozygous SMNt deletion has been found, whereas 5% of centromeric SMN (SMNc) deletions can be observed. Although SMNt deletions appear causal for infantile and at least some adult-onset spinal muscular atrophy (SMA) (type IV), the respective role of SMN deletions remains unclear in adult-onset MNDs. We studied SMN gene in three different groups of patients with adult-onset MNDs. In sporadic amyotrophic lateral sclerosis (ALS; n = 177) ands familial ALS (n = 66), no SMNt deletion had been found, and the frequency of SMNc deletions was not increased. Converesly, among the 14 patients with sporadic pure lower MND (LMND), we found 2 patients with homozygous SMNt deletions (14%) and 5 patients with homozygous SMNc deletions (36%). These data suggest that (1) SMNt deletions do not account for the major part, if any, of adult-onset LMND cases; and (2) SMNc deletions act as a susceptibility factor for LMNDs in adults. The clinical and gentic heterogeneity of LMND cases, including SMA type IV, are yet to be unexplained. Further studies on large groups of adult-onset LMND patients are warranted to refine its nosology.     

脊髓性肌萎缩症的快速基因诊断研究

目的研究我国近端型脊髓性肌萎缩症（ＳＭＡ）患者的运动神经元生存基因（ＳＭＮ）外显子的缺失情况,探讨其快速基因诊断的可行性和临床应用价值。方法应用ＰＣＲ－酶切法检测２６例确诊的ＳＭＡ患者及２０名正常对照ＳＭＮ基因的第７、８号外显子的缺失情况。结果在２６例及２５例患者中,分别发现缺失了端粒ＳＭＮ基因（ＳＭＮ１）的第７和８号外显子,缺失率达１００％（２６／２６）和９６％（２５／２６）,而正常对照及患者的家系成员均未发现外显子缺失。结论应用ＰＣＲ－酶切法检测ＳＭＮ１基因缺失从而进行ＳＭＡ患者的基因诊断,具有准确、简便和快速的优点。     

SMN1 gene study in three families in which ALS and spinal muscular atrophy co-exist

Spinal muscular atrophy (SMA) is caused by SMN1 gene deletions or mutations, and ALS is the most frequent motor neuron condition in adults. The authors describe three families in which ALS and SMA coexist. The authors found that no SOD1 mutation was found within these families; all three ALS cases had at least two SMN1 copies; and an abnormal SMN1 gene locus did not explain the co-occurrence of these two motor neuron disorders in these families.     

应用多重连接依赖性探针扩增技术进行脊髓性肌萎缩症产前诊断

目的 探讨多重连接依赖性探针扩增技术在脊髓性肌萎缩症产前诊断中的临床应用价值.方法 以脊髓性肌萎缩症6个家系作为研究对象.包括患者7例、父母12名、胎儿6例.采用多重连接依赖性探针扩增技术对运动神经元生存(SMN)基囚及脊髓性肌萎缩症修饰基因进行分析,应用聚合酶链反应-限制性酶切片段长度多态性技术检测SMNI基凶缺失,羊水标本分别通过直接离心沉淀和细胞培养进行DNA分析.结果 多重连接依赖性探针扩增分析提示6个家系中7例患者及1例胎儿(家系Ⅳ)呈SMNI基凶纯合缺失,与聚合酶链反应.限制性酶切片段长度多态性分析结果一致;11名父母及5例胎儿的SMNI拷贝数为1,1名母亲(家系V)SMNI拷贝数为2,均为脊髓性肌萎缩症携带者.多重连接依赖性探针扩增分析显示.6个家系中10名成员SMN2拷贝数为1,15名成员SMN2拷贝数为2;多重连接依赖性探针扩增分析.6个家系中3名成员神经元凋亡抑制蛋白(NAIP)基冈缺失,其余家系成员正常.结论 多重连接依赖性探针扩增技术为一快速而可靠的基凶榆测及定量分析方法,可准确检测SMN基凶及脊髓性肌萎缩症修饰基凶的缺失突变并分析基因拷贝数,适用于脊髓性肌萎缩症患者、携带者的基因诊断及产前诊断.     

Correlation between deletion patterns of SMN and NAIP genes and the clinical features of spinal muscular atrophy in Indian patients

BACKGROUND: Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder involving degeneration of anterior horn cells of spinal cord resulting in progressive muscle weakness and atrophy. AIMS: The molecular analysis of two marker genes for spinal muscular atrophy (SMA) i.e, the survival motor neuron gene (SMN) and the neuronal apoptosis inhibitory protein gene (NAIP) was conducted in 39 Indian patients with clinical symptoms of SMA. Out of these, 28 showed homozygous deletions and the phenotypic features of these SMA patients were compared with the corresponding genotypes. SETTINGS: A tertiary care teaching Hospital. DESIGN: This is a prospective hospital based study. MATERIALS AND METHODS: Polymerase chain reaction (PCR) combined with restriction fragment length polymorphism (RFLP) was used to detect the deletion of exon 7 and exon 8 of SMN1 gene, as well as multiplex PCR for exon 5 and 13 of NAIP gene. RESULTS: Exons 7 and 8 of SMN and NAIP (exon 5) were homozygously deleted in 73% of SMA I and 27% of SMA II patients. SMN exon 7 and 8 deletions without NAIP deletions were seen in 27% of type I SMA and 46% of SMA type II patients. Two patients of type III SMA showed single deletion of SMN exon 7 along with 27% of SMA type II patients. CONCLUSION: With the advent of molecular biology techniques, SMN gene deletion studies have become the first line of investigation for confirmation of a clinical diagnosis of SMA. The findings of homozygous deletions of exons 7 and/or 8 of SMN1 gene confirms the diagnosis of SMA, even in patients with atypical clinical features. Deletions of NAIP gene were mainly seen in severely affected patients, hence is useful for predicting the prognosis.     

Quantitative analysis of SMN2 based on real-time PCR: correlation of clinical severity and SMN2 gene dosage

Spinal muscular atrophy (SMA) is a common autosomal recessive disorder, caused by homozygous deletion of the survival motor neuron gene 1 (SMN1). SMN2, a gene highly homologous to SMN1, is considered to influence the severity of SMA. Patients with SMA have been classified into three types on the basis of age at onset and clinical severity. In the present study, we performed a quantitative analysis of SMN2 in 22 patients of SMA to further clarify the correlation between clinical severity and SMN2 gene dosage. We determined the SMN2 gene copy number based on real-time PCR. In 3 Type I patients with only one SMN2 copy, the clinical phenotype was the severest. The remaining 14 Type I patients had two or three copies of the SMN2 gene, and showed a variable clinical severity. A patient with 3 copies required artificial ventilation at 2 months old. Five Type II and Type III patients had at least 4 copies of the SMN2 gene. Although the SMN2 gene dosage correlates the clinical severity, the mechanism by which SMN2 shows compensation in some Type I patients remains to be determined.     

Study of Survival of Motor Neuron (SMN) and Neuronal Apoptosis Inhibitory Protein (NAIP) gene deletions in SMA patients

In view of the paucity of deletion studies of survival of motor neuron (SMN) and neuronal apoptosis inhibitor protein (NAIP) genes in Indian SMA patients, this study has been undertaken to determine the status of SMN1, SMN2 and NAIP gene deletions in Indian SMA patients. Clinically and neurophysiologically diagnosed SMA patients were included in the study. A gene deletion study was carried out in 45 proximal SMA patients and 50 controls of the same ethnic group. Both SMN1 and NAIP genes showed homozygous absence in 76 % and 31 % respectively in proximal SMA patients. It is proposed that the lower deletion frequency of SMN1 gene in Indian patients may be due to mutations present in other genes or population variation, which need further study.     

Demonstration of acute ischemic lesions in the fetal brain by diffusion magnetic resonance imaging

The etiology of amyotrophic lateral sclerosis remains unknown in the majority of cases. Homozygous SMN1 (survival motor neuron) gene deletion causes spinal muscular atrophy, and SMN2 gene deletions are possible risk factors in lower motor neuron disease. We studied SMN1 and SMN2 genes copy numbers in 167 amyotrophic lateral sclerosis patients and in 167 matched controls. We noted that 16% of amyotrophic lateral sclerosis patients had an abnormal copy number of the SMN1 gene (1 or 3 copies), compared with 4% of controls. An abnormal SMN1 gene locus may be a susceptibility factor for amyotrophic lateral sclerosis.     

Spinal muscular atrophy: Diagnosis and management in a new therapeutic era

Spinal muscular atrophy (SMA) describes a group of disorders associated with spinal motor neuron loss. In this review we provide an update regarding the most common form of SMA, proximal or 5q‐SMA, and discuss the contemporary approach to diagnosis and treatment. Electromyography and muscle biopsy features of denervation were once the basis for diagnosis, but molecular testing for homozygous deletion or mutation of the SMN1 gene allows efficient and specific diagnosis. In combination with loss of SMN1, patients retain variable numbers of copies of a second similar gene, SMN2, which produces reduced levels of the survival motor neuron (SMN) protein that are insufficient for normal motor neuron function. Despite the fact that understanding of how ubiquitous reduction of SMN protein leads to motor neuron loss remains incomplete, several promising therapeutics are now being tested in early‐phase clinical trials. Muscle Nerve 51 : 157–167, 2015     

Homozygous exon 7 deletion of the SMN centromeric gene (SMN2): A potential susceptibility factor for adult-onset lower motor neuron disease

Mutations in the telomeric copy of the SMN gene (SMN1) are responsible for almost all infantile motor neuron disease (MND). In contrast, the role of the centromeric copy of the SMN gene (SMN2) in MND remains unclear. We searched for deletions of SMN1 and SMN2 in a group of 11 patients with sporadic adult-onset lower motor neuron disease (also referred to as “progressive muscular atrophy”) and found an excess of patients carrying homozygous deletions of SMN2 exon 7 (36 % versus 5 % in the normal population). This result suggests that SMN2 deletions could act as a susceptibility factor for sporadic lower motor neuron disease in adults. Received: 8 April 2001, Received in revised form: 22 June 2001, Accepted: 28 June 2001     

散发性肌萎缩侧索硬化与运动神经元生存基因缺失的关系

目的 探讨我国散发性肌萎缩侧索硬化(SALS)与运动神经元生存基因(SMN)缺失之间的关系.方法 收集141例SALS患者和134名健康对照的外周静脉血并抽提DNA,应用聚合酶链反应.限制性片段长度多态性(PCR-RFLP)进行SMN基因缺失筛查.缺失频率的比较采用卡方检验分析.结果 4例SALS患者和3名健康对照分别检出SMN2基因第7、8号外显子纯合缺失,缺失频率分别为2.84%(4/141)和2.24%(3/134),差异无统计学意义(χ2=0.0001,P=1.000).此外,所有研究对象均未检出SMN1基因纯合缺失.结论 SMN基因纯合缺失与我国SALS患者之间无明显相关性.     

Combination of SMN2 copy number and NAIP deletion predicts disease severity in spinal muscular atrophy

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder caused by mutations in the SMN1 gene. The SMN2 gene is highly homologous to SMN1 and has been reported to be correlated with severity of the disease. The clinical presentation of SMA varies from severe to mild, with three clinical subtypes (type I, type II, and type III) that are assigned according to age of onset and severity of the disease. Here, we aim to investigate the potential association between the number of copies of SMN2 and the deletion in the NAIP gene with the clinical severity of SMA in patients of Malaysian origin. Forty-two SMA patients (14 of type I, 20 type II, and 8 type III) carrying deletions of the SMN1 gene were enrolled in this study. SMN2 copy number was determined by fluorescence-based quantitative polymerase chain reaction assay. Twenty-nine percent of type I patients carried one copy of SMN2, while the remaining 71% carried two copies. Among the type II and type III SMA patients, 29% of cases carried two copies of the gene, while 71% carried three or four copies of SMN2. Deletion analysis of NAIP showed that 50% of type I SMA patients had a homozygous deletion of exon 5 of this gene and that only 10% of type II SMA cases carried a homozygous deletion, while all type III patients carried intact copies of the NAIP gene. We conclude that there exists a close relationship between SMN2 copy number and SMA disease severity, suggesting that the determination of SMN2 copy number may be a good predictor of SMA disease type. Furthermore, NAIP gene deletion was found to be associated with SMA severity. In conclusion, combining the analysis of deletion of NAIP with the assessment of SMN2 copy number increases the value of this tool in predicting the severity of SMA.     

Spinal muscular atrophy due to double gene conversion event

Spinal muscular atrophy (SMA) is an autosomal recessive disease characterized by degeneration of the anterior horn cells of the spinal cord. The survival motor neuron (SMN) gene has been identified as an SMA-determining gene. SMN exists as two copies in 5q13, and deletions in exons 7 and 8 of the telomeric copy (SMN(T)) occur in 95% of patients, regardless of disease severity. In a minority of patients, exon 7 but not exon 8 of SMN(T) appears deleted. We now report a patient with typical features of SMA type II who carried homozygous deletions of SMN(T) exon 7 and centromeric SMN (SMN(C)) exon 8 but retained SMN(T) exon 8 and SMN(C) exon 7. Sequence analysis demonstrated that SMN(C) exon 7 was adjacent to SMN(T) exon 8 on both SMN copies, indicating a double conversion. We confirm that sequence conversion is a common event in SMA and is associated with the milder form of the disease. The severity, however, can be modified in either positive or negative direction by other factors.     

单链构象多态技术检测脊髓性肌萎缩症基因缺失

目的探讨中国人脊髓性肌萎缩症（ＳＭＡ）基因诊断的可行性。方法应用聚合酶链反应单链构象多态（ＰＣＲＳＳＣＰ）技术研究来自１６个家系的２０例ＳＭＡ患者及２０名正常对照的运动神经元生存（ＳＭＮ）基因的第７、８号外显子的缺失情况。结果２０例患者均缺失端粒ＳＭＮ（ＳＭＮＴ）基因的第７号外显子，１９例患者缺失第８号外显子，而正常对照均无外显子缺失。结论应用直接检测ＳＭＮＴ基因缺失的方法可准确快速地诊断中国人ＳＭＡ患者     

Insights into genotype-phenotype correlations in spinal muscular atrophy: a retrospective study of 103 patients

Spinal muscular atrophy (SMA) is an autosomal recessive disorder associated with homozygous deletion of the survival motor neuron 1 gene (SMN1). Its centromeric copy gene, SMN2, is the major modifying factor. However, the genotype-phenotype correlation is incomplete and is therefore not useful in clinical practice. We studied a cohort of 103 patients in order to refine this correlation. In addition to standard disease severity data, we collected three additional criteria: age at death; brainstem involvement; and loss of ambulation. Gene dosage analysis was conducted by multiplex ligation-dependent probe amplification (MLPA). SMN2 copynumber was highly correlated with survival duration in SMA type I and ambulation conservation or loss in type III. Among SMA severity groups, it was not significantly different in cases with brainstem involvement. Although the SMN2 copynumber could provide prognostic indications, clinical discrepancies still exist among patients, suggesting the existence of unidentified modifying factors.     

The molecular basis of spinal muscular atrophy (SMA) in South African black patients

SMA is an autosomal recessive disorder that results in symmetrical muscle weakness and wasting due to degeneration of the anterior horns of the spinal cord. The gene for SMA, the survival motor neuron (SMN) gene is found on chromosome 5q13, in a region harbouring a 500kb duplication, resulting in two copies (a telomeric and a centromeric) of each of the genes found within the duplication. SMN1 is homozygously deleted in approximately 95% of patients worldwide. Results of the current study show that only 51% (42/92) of South African black SMA patients have homozygous deletions of the SMN1 gene. This frequency is significantly lower than observed in the South African white patient group and in other international populations. The pattern of deletions in the South African black patients is also significantly different. In order to elucidate the molecular basis of SMA in the black population, a dosage assay enabling the detection of SMN1 deletion heterozygotes was independently developed. This assay confirmed SMN1 heterozygosity in at least 70% of black non-deletion SMA patients. However, no second disease-causing mutation or a common chromosomal background for this mutation could be identified in these patients. The frequency of SMA in both the black and white population was also determined using the SMN1 gene dosage assay. Results showed that SMA is more common than previously thought with carrier rates of 1 in 50 and 1 in 23 and a predicted birth incidence of 1 in 3574 and 1 in 1945 in the black population and the white population, respectively. Development and incorporation of the SMN1 dosage assay into the molecular diagnostic service will increase the percentage of cases in which the diagnosis of SMA can be confirmed and allow preclinical and prenatal diagnosis. Further gene characterisation and functional studies would need to be performed in order to further define the molecular basis of SMA in the South African black population.     

Analysis of point mutations in the SMN1 gene in SMA patients bearing a single SMN1 copy

Spinal muscular atrophy (SMA) is caused by homozygous deletion of the SMN1 gene in approximately 96% of cases. Four percent of SMA patients have a combination of the deletion or conversion on one allele and an intragenic mutation on the second one. We performed analysis of point mutations in a set of our patients with suspicion of SMA and without homozygous deletion of the SMN1 gene. A quantitative test determining SMN1 copy number (using real-time PCR and/or MLPA analysis) was performed in 301 patients and only 1 SMN1 copy was detected in 14 of them. When these 14 patients were screened for the presence of point mutations we identified 6 mutations, p.Y272C (in three patients) and p.T274I, p.I33IfsX6, and p.A188S (each in one case). The mutations p.I33IfsX6 and p.A188S were found in two SMAI patients and were not detected previously. Further, evaluation of the relationship between mutation type, copy number of the SMN2 gene and clinical findings was performed. Among our SMA patients with a SMN1 homozygous deletion, we found a family with two patients: the son with SMAII possesses 3 SMN2 copies and the nearly asymptomatic father has a homozygous deletion of SMN1 exon 7 and carries 4 SMN2 copies. Generally, our results illustrate that an increased SMN2 gene copy number is associated with a milder SMA phenotype.     

Hydroxyurea enhances SMN2 gene expression in spinal muscular atrophy cells

Spinal muscular atrophy (SMA) is a motor neuron disease caused by dysfunction of the survival motor neuron (SMN) gene. Human SMN gene is present in duplicated copies: SMN1 and SMN2. More than 95% of patients with SMA lack a functional SMN1 but retain at least one copy of SMN2. Unlike SMN1, SMN2 is primarily transcribed into truncated messenger RNA and produces low levels of SMN protein. We tested a therapeutic strategy by treating cultured lymphocytes from patients with SMA with hydroxyurea to modify SMN2 gene expression and to increase the production of SMN protein. Twenty lymphoblastoid cell lines (15 SMA and 5 control lines) were treated with hydroxyurea at 5 concentrations (0.5, 5, 50, 500, and 5,000 microg/ml) and 3 time points (24, 48, and 72 hours). SMN2 gene copy numbers were determined using real-time quantitative polymerase chain reaction. Hydroxyurea treatment resulted in a time-related and dose-dependent increase in the ratio of full-length to truncated SMN messenger RNA. SMN protein levels and intranuclear gems also were significantly increased in these hydroxyurea-treated cells. The SMN2 gene copy number correlated inversely with the SMA phenotypic severity. This study provides the first evidence for a therapeutic indication of hydroxyurea in SMA.