Compound mutations (R237X and L375P) in the fumarylacetoacetate hydrolase gene causing tyrosinemia type I in a Chinese patient

Background  Mutations in fumarylacetoacetate hydrolase (FAH) gene can lead to tyrosinemia type 1 (HT1), a relatively rare autosomal recessive disorder. To date, no molecular genetic defects of HT1 in China have been described. We investigated a Chinese family with a HT1 child to identify mutations in FAH.

Methods  DNA sequencing was used for mutations screening in FAH gene. Real-time polymerase chain reaction (PCR) was performed to determine the FAH gene expression level. To confirm the presence of degradation by the nonsense-mediated mRNA decay pathway (NMD), the fragments containing R237X mutations were analyzed by primer introduced restriction analysis-polymerase chain reaction (PIRA-PCR) and cDNA sequencing. Finally, the effects of the mutations reported in this study were predicted by online softwares.

Results  A boy aged 3 years and 8 months was diagnosed clinically with HT1 based on his manifestations and biochemical abnormalities. Screening of FAH gene revealed two heterozygous mutations R237X and L375P transmitted from his mother and father respectively. In this pedigree, the amount of FAH mRNA relative to a healthy control was 0.44 for the patient, 0.77 for his mother and 1.07 for his father. Moreover, both PIRA-PCR and cDNA sequencing showed significant reduction of the FAH mRNA with R237X nonsense mutation. The missense mutation of L375P was not reported previously and prediction software showed that this mutation decreased the stability of protein structure and affected protein function.

Conclusions  This is the first case of HT1 analyzed by molecular genetics in China. The R237X mutation in FAH down- regulates the FAH gene expression, and the L375P mutation perhaps interrupts the secondary structure of FAH protein.

     

Rapid genetic diagnosis and prenatal diagnosis of spinal muscular atrophy by denaturing high-performance liquid chromatography

Spinal muscular atrophy （SMA） is a common Pautosomal recessive neuromuscular disorder （1in 6000 to 10 000 births） caused by mutations in the SMN1 gene at 5q13. More than 90%-98% of SMA patients show homozygous deletion of SMN1, which has proved to be useful in the diagnosis of SMA. But it is hampered because of the existence of a highly homologous gene, SMN2. Based on nucleotide mismatches between SMN1 and SMN2, the following two DNA tests are usually performed： single-strand conformational polymorphism （SSCP） and polymerase chain reaction （PCR） followed by a restriction enzyme digestion.In this study we developed a new method for rapid genetic diagnosis of SMA by denaturing high-performance liquid chromatography （DHPLC）, which is based on different retention of homoduplexes and heteroduplexes in detecting the homozygous deletion of SMN1. Both genetic and prenatal diagnoses were performed successfully for a SMA family by DHPLC, which was confirmed as a rapid and effective technique for detecting the deletion of SMN1.     

A novel missense mutation of the TYR gene in a pedigree with oculocutaneous albinism type 1 from China

Background  The mutation of the tyrosinase (TYR) gene results in oculocutaneous albinism type 1 (OCA1), an autosomal recessive genetic disorder. OCA1 is the most common type of OCA in the Chinese population. Hence, the TYR gene was tested in this study. We also delineated the genetic analysis of OCA1 in a Chinese family.

Methods  Genomic DNA was isolated from the blood leukocytes of a proband and his family. Mutational analysis at the TYR locus by DNA sequencing was used to screen five exons, including the intron/exon junctions. A pedigree chart was drawn and the fundus of the eyes of the proband was also examined.

Results  A novel missense mutation p.I151S on exon 1, and homozygous TYR mutant alleles were identified in the proband. None of the mutants was identified among the 100 normal control subjects. Genetic analysis of the proband’s wife showed normal alleles in the TYR gene. Thus, the fetus was predicated a carrier of OCA1 with a normal appearance.

Conclusion  This study provided new information about a novel mutation, p.I151S, in the TYR gene in a Chinese family with OCA1. Further investigation of the proband would be helpful to determine the effects of this mutation on TYR activity.

     

Exome sequencing identifies compound heterozygous PKHD1 mutations as a cause of autosomal recessive polycystic kidney disease

Background  Autosomal recessive polycystic kidney disease (ARPKD) is a rare inherited disease, which is a disorder with multiple organ involvement, mainly the kidney and liver. It is caused by mutations in the PKHD1 gene. Here, we reported the clinical characteristics of a case with ARPKD and analyze the genetic features of this patient as well as of his father using targeted exome sequencing and Sanger sequencing.

Methods  Genomic DNA was extracted from peripheral blood leukocytes obtained from a patient with ARPKD. The mutations were identified using exome sequencing and confirmed by Sanger sequencing.

Results  The patient was diagnosed as ARPKD based on ultrasonography and abdominal computed tomography which showed polycystic changes, multiple calcinosis of both kidneys, and multiple dilated bile ducts of the liver. Compound heterozygous PKHD1 gene mutations A979G and G5935A, which lead to substitution of an asparagine for an aspartate at amino acid 327 (N327D) and a glycine for an arginine at amino acid 1979 (G1979R) respectively, were identified using targeted exome sequencing and confirmed by Sanger sequencing for the patient. In addition, the father of the patient was identified to be a carrier of heterozygous A979G mutation of this gene.

Conclusions  We identified that the compound heterozygous PKHD1 gene mutations are the molecular basis of the patient with ARPKD. Targeted exome sequencing is suitable for genetic diagnosis of single-gene inherited diseases like ARPKD in which the pathogenic gene is a large.     

Identification of seven novel mutations in the factor VIII gene in 18 unrelated Chinese patients with hemophilia A

Background  Hemophilia A (HA) is an X-linked inherited bleeding disorder caused by decreased activity of factor VIII (FVIII) due to heterogenous mutations in the FVIII coding gene (F8). The type of mutation plays an important role in the FVIII inhibitor formation. To date, several studies on the spectra of F8 defects have been performed in Western populations, but similar studies in Asian races are scarce. Here, we reported the distribution of the F8 gene mutations in 18 unrelated Chinese patients with HA.
Methods  Intron 22 and intron 1 inversions in the F8 gene were screened in 158 unrelated patients with HA using a long-distance PCR and multiplex PCR method. Direct sequencing of the coding region of the F8 gene was used to identify the mutations responsible for HA in 18 unrelated Chinese HA patients who were negative for intron 22 and intron 1 inversions; sequences were compared with the HAMSTeRS database. A clotting method was used to assay the FVIII activity level and the Bethesda assay was used to detect the FVIII inhibitor.
Results  A total of 18 different HA F8 mutations were identified, seven of which were described for the first time. These novel mutations included five small deletions, one point mutation and one small insertion. One novel mutation (4382-3 AC deletion) was associated with inhibitor development.
Conclusion  These data extend our insight into the mechanisms by which novel amino acid mutations may lead to HA and how the HA patient genotypes influence the risk of FVIII inhibitor.

     

Prenatal diagnosis of Werdnig Hoffmann disease in China

Objective To establish a means for prenatal prediction of spinal muscular atrophy (SMA) through survival motor neuron (SMN) gene deletion analysis and genetic counseling in families with a child affected with SMA.
Methods Genetic analysis for prenatal prediction of Werdnig-Hoffmann disease was performed in a at risk Chinese family by polymerase chain reaction (PCR)-single-strand conformation polymorphism (SSCP) in SMN gene exons 7 and 8.
Results The pregnancy was positive for the homozygous deletion of the SMN gene, thus the fetus was diagnosed as being affected and the pregnancy was terminated.
Conclusion This approach is fast and reliable for DNA-based prenatal diagnosis of Werdnig-Hoffmann disease.     

Novel mutations of PRSS1 gene in patients with pancreatic cancer among Han population

Background  A high mortality rate of pancreatic cancer becomes a bottleneck for further treatment with long-term efficacy. It is urgent to find a new mean to predict the early onset of pancreatic cancer accurately. The authors hypothesized that genetic variants of cationic trypsinogen (PRSS1) gene could affect trypsin expression/function and result in abnormal activation of protease activated receptor-2 (PAR-2), then lead to pancreatic cancer. The aim of this study was to elaborate some novel mutations of PRSS1 gene in the patients with pancreatic cancer.

Methods  Totally 156 patients with pancreatic cancer and 220 unrelated individuals as controls were enrolled in this study. The mutations of PRSS1 gene were analyzed by direct sequencing. K-ras Mutation Detection Kit was used to find the general k-ras gene disorder in the pancreatic cancer tissue. Then the clinical data were collected and analyzed simultaneously.

Results  There were two patients who carried novel mutations which was IVS 3 +157 G>C of PRSS1 gene in peripheral blood specimens and pancreatic cancer tissue. What’s more, it was surprising to find a novel complicated mutation of exon 3 in PRSS1 gene (c.409 A>G and c.416 C>T) in another young patient. The complicated mutation made No.135 and No.137 amino acid transfer from Thr to Ala and Thr to Met respectively. No any mutation was found in the normal controls while no mutations of k-ras gene were detected in the three patients.

Conclusion  Mutations of PRSS1 gene may be an important factor of pancreatic cancer.

     

Comparison of three methods for detecting epidermal growth factor receptor mutations in plasma DNA samples of Chinese patients with advanced non-small cell lung cancer

Background  Epidermal growth factor receptor (EGFR) mutations can predict tumor response to tyrosine kinase inhibitors (TKIs). Detecting EGFR mutations in plasma DNA samples in patients with advanced non-small cell lung cancer is challenging and promising. We compared three methods for detecting plasma EGFR mutations, including direct DNA sequencing, denaturing high-performance liquid chromatography (DHPLC) and Scorpions Amplification Refractory Mutation System (Scorpions ARMS).

Methods  Plasma DNA samples from 73 patients with stage IIIB to IV adenocarcinoma were analyzed for EGFR mutations in exons 19 (deletion mutation) and 21 (L858R mutation) using direct DNA sequencing, DHPLC and Scorpions ARMS. Sensitivities of the three methods were compared and the relationship between EGFR mutations and patients’ survival was analyzed.

Results  In 73 patients, we detected EGFR mutations in 5 samples (6.9%) by direct DNA sequencing, in 22 samples (30.1%) by DHPLC, and in 28 samples (38.4%) by Scorpions ARMS. EGFR mutations were found in 13 samples in exon 19 and in 9 samples in exon 21 by DHPLC, while we found mutations in 15 samples in exon 19 and in 13 samples in exon 21 by Scorpions ARMS. Among the 73 patients, there was 90.4% concordance between DHPLC and Scorpions ARMS (66/73, κ=0.79, P=0.07). Of the 73 patients, 46 patients were treated with gefitinib, including 18 patients with mutations and 28 patients without mutations as determined by Scorpions ARMS. The 18 patients with mutations had a significantly longer progression-free survival (PFS) time (median PFS was 21.0 months) than the 28 patients without mutations (median PFS was 7.0 months) (P=0.022).

Conclusions  Among the three methods for detecting EGFR mutations in plasma DNA samples of patients with advanced lung adenocarcinoma, direct gene sequencing had the lowest sensitivity, while Scorpion ARMS showed the highest mutation detecting capability. DHPLC is slightly less sensitive than Scorpion ARMS. EGFR mutations in exons 19 (deletion mutation) and 21 (L858R mutation) predict a longer PFS.

     

Genetic diagnosis of Liddle’s syndrome by mutation analysis of SCNN1B and SCNN1G in a Chinese family

Background  Liddle’s syndrome is a rare autosomal-dominant monogenic form of salt-sensitive hypertension. This study aimed to screen the gene mutation in β and γ subunits of the epithelial sodium channel (ENaC) of a Chinese family with Liddle’s syndrome, an autosomal dominant form of hypertension.

Methods  DNA samples from the proband with early-onset, treatment-resistant hypertension and suppressed plasma renin activity were initially screened for mutations in the C-terminal exons of the ENaC β or γ subunit genes, using amplification by polymerase chain reaction and direct DNA sequencing. We also screened the C-terminus of SCNN1B and SCNN1G in family members, and screened for the mutation in 150 controls.

Results  Genetic analysis of the β ENaC gene revealed a missense mutation of CCC to TCC at codon 616 in the proband, her mother and her grandmother. One hundred and fifty randomly selected controls had not the mutation, indicating that this is not a common genetic polymorphism. There was no mutation of the γ ENaC gene in any of the individuals examined.

Conclusions  Through direct DNA sequencing analysis, we established the diagnosis of Liddle’s syndrome for the proband and her families, and provided tailored therapies to this abnormality. These results provide further evidence that Pro616Ser is a critical amino acid that has a key role in the inhibition of sodium channel activity.

     

中国西南地区汉族脊肌萎缩症患者SMA相关基因分子特征

目的 以中国西南地区汉族人群为研究对象,构建脊肌萎缩症（SMA）相关基因拷贝数变化频率,为SMA的临床诊断和分型提供依据。方法 收集62例临床诊断为SMA的无亲缘关系患者,以及50例无亲缘关系的正常人作为健康对照组,采用多重连接酶依赖的探针扩增技术（MLPA）分析运动神经元基因（SMN）和神经原凋亡抑制蛋白基因（NAIP）的拷贝数。 结果 62例患者中,SMAⅠ～Ⅳ型分别占30.65%（19/62）、41.94%（26/62）、16.13%（10/62）、11.29%（7/62）。SMN1基因外显子7纯合缺失占98.38%（61/62）,SMN1基因外显子8纯合缺失占82.26%（51/62）。SMAⅠ型患者中NAIP基因外显子5有68.42%（13/19)纯合缺失,26.32%（5/19）杂合缺失;SMAⅡ～Ⅳ型患者中NAIP基因外显子5有13.95%（6/43）纯合缺失,62.79%（27/43）杂合缺失。SMAⅠ型患者中68.42%（13/19）有1～2拷贝的SMN2基因,SMAⅡ型中84.62%（22/26)有2拷贝以上的SMN2基因,90.00%（9/10)SMAⅢ型和85.71%（6/7)SMAⅣ型患者有2拷贝以上的SMN2基因,且发现有5拷贝和6拷贝SMN2基因。结论 SMN1基因缺失是SMA的主要致病原因,SMN2和NAIP基因拷贝数变化可以影响SMA病情严重程度。     

SMN基因缺失多重连接探针扩增法检测和识别脊柱肌肉萎缩症的纯合型或杂合型SMN基因缺失

Objective: Spinal muscular atrophy(SMA), an autosomal recessive neuromuscular degen-eration of the anterior horn ceils of the spinal cord and brain stem, results in one of the most common dis-eases with muscle fatigue and atrophy. Most SMA cases including all the types are due to the homozygous deletion of at least exon 7 within the survival motor neuron 1 (SMN-1) gene. Although a ““golden stand-ard““ assay ( PCR with mismatch primer followed by enzyme digestion) is very reliable for the identifica-tion of homozygous SMN-1 deletion, the carrier detection of heterozygous SMN-1 deletion remains a chal-lenge. Methods: Some PCR-based gene dosage assays or multiplex PCR allow for the determination of the copy number of SMN-1 gene to identify heterozygous deletion, but these procedures are often time consuming and available on a limited clinical basis. Recently developed MLPA (multiplex ligation-de-to establish the copy number of the SMN gene. We performed a validation for simultaneous detection of homozygous SMN-1 deletions of SMA patients and heterozygous SMN-1 deletions of SMA carriers in a sim-ple assay using a MLPA-SMA assay specific reagent. Results: Six out of 20 patients with SMA were found to have homozygous SMN-1 deletion, confirmed by the PCR/digestion assay. All 4 parents of the children with SMA had heterozygous SMN-1 deletion, confirmed by an independent relative quantitative analysis. Conclusion: MLPA provides a simple, rapid and accurate method of simultaneously detecting homozygous deletions and heterozygous deletions in a sinzle assay for both SMN-1 and SMN-2 zenes.     

MLPA方法在脊髓性肌肉萎缩症分子诊断中的应用

目的 探讨多重连接依赖性探针扩增(MLPA)技术在脊髓性肌肉萎缩症(SMA)分子诊断中的应用.方法 从13例SMA患者、31名患者父母的外周血标本和10份胎儿羊水标本,以及50名正常人外周血标本中提取基因组DNA,应用MLPA技术进行分析,同时也行常规聚合酶链反应-限制性片段长度多态性(PCR-RFLP)和位点特异性PCR分析.结果 MLPA分析结果与常规PCR-RFLP和位点特异性PCR结果相符:13例患者的运动神经元存活基因(SMN)1基因均呈纯合缺失,SMN2基因拷贝数的增加与SMA表型的严重程度(从I型到Ⅲ型)存在显著性差异(P<0.05);31名患者父母SMN1基因1拷贝的人数为29(占93.5%),2拷贝的为2(占6.5%);50名正常健康成人SMN1基因1拷贝的人数为1(占2.0%),2拷贝的为48(占96.O%);SMA患者父母组和健康正常成人组之间的SMN1基因拷贝数存在显著件差异(P<0.01);10例胎儿中2例存在SMN1的纯合缺失.结论 MLPA是一种准确可靠的SMA分子诊断新方法.     

运用DHPLC技术分析非纯合缺失型脊髓性肌萎缩症患儿的SMN基因拷贝数

目的 建立一种准确、快捷的方法,定量检测运动神经元存活基因(SMN)的拷贝数,以便分析非纯合缺失型脊髓性肌萎缩症(SMA)患儿中SMNl基因的杂合性缺失.方法 应用等位基因特异PCR(AS-PCR)分别进行SMN1与SMN2基因的特异扩增,用另外2个无关基因作内对照,进行变性高效液相色谱法(DHPLC)分析,确定基因拷贝数.结果 (1)改进的双重AS-PCR与DHPLC相结合的技术,能够有效分离SMN1和SMN2基因,通过与对照基因的对比,可准确地判断SMN基因的拷贝数,SMN1和SMN2基因1～4拷贝之间不存在重叠.(2)38例非纯合缺失SMA患儿中,20例的SMN1基因为1个拷贝(52.6%),判断为SMN1基因的杂合性缺失,其中15例(75.0%,15/20)的SMN2基因为2个拷贝,5例(25.0%,5/20)SMN2基因为3个拷贝.(3)30名SMN1基因纯合缺失型突变患者的双亲中,有24名(80.0%)的SMNl基因为1个拷贝.结论 本研究所建立的方法能够准确、快捷地检测SMN基因的拷贝数.     

SMN基因诊断小儿脊髓性肌萎缩症

目的了解儿童期发作的进行性脊髓性肌萎缩(SMA)患者的运动神经元存活基因(SMN)的缺失,探讨聚合酶链反应-限制性片段长度多态性(PCR-RFLP)方法用于SMA疾病的诊断价值。方法应用PCR-RFLP方法对3例SMA可疑患儿及其父母5例的SMN1基因外显子7和8进行了检测,并对其进行基因测序。结果3例SMA可疑患儿中3例均有SMN1基因缺失,为外显子7和8联合缺失。其父母均无SMN1基因缺失。基因测序支持诊断。结论用PCR-RFLP法对高度可疑儿童型SMA的病例进行诊断,具有较高敏感性和特异性,简便易行。     

进行性脊髓性肌萎缩症患者神经元存活基国及神经元凋亡抑制蛋白基因的缺失

目的：研究中国人群中进行性脊髓性肌萎缩症（ｓｐｉｎａｌ ｍｕｓｃｕｌａｒ ａｔｒｏｐｈｙ,ＳＭＡ）患者中神经元存活基因（ｓｕｒｖｉｖａｌ ｍｏｔｏｒ ｎｅｕｒｏｎ,ＳＭＮ）外显子７及神经元调亡抑制蛋白基因（ｎｅｕｒｏｎａｌ ａｐｏｐｔｏｓｉｓ ｉｎｈｉｎｂｉｔｏｒｙ ｐｒｏｔｅｉｎ ｇｅｎｅ,ＮＡＩＰ）外显子５缺失情况,进一步探讨这２个ＳＭＮ基因外显子７区域和５５例患儿ＮＡＩＰ基因外显子５的缺失进行检测。结果：ＳＭＮ基因外显子７区域纯合缺失率分别为：ＳＭＡＩ型９２％（２３／２５）;Ⅱ型９０％（２７／３０）。患儿双亲中有２例母亲的１例父亲也有纯合缺失。在５５例ＳＭＡ患儿中未检测到有ＮＡＩＰ基因外显子５的纯合缺失,仅发现２例杂合性缺失。结论：中国人ＳＭＡ患者中ＳＭN     

Identification and analysis of mutations of the Wilson disease gene in Chinese population

Ｗｉｌｓｏｎｄｉｓｅａｓｅ (ＷＤ)ｉｓａｌｅｔｈａｌａｕｔｏｓｏｍａｌｒｅｃｅｓｓｉｖｅｄｉｓｏｒｄｅｒｏｆｃｏｐｐｅｒｍｅｔａｂｏｌｉｓｍ ,ａｎｄｉｓｃｈａｒａｃｔｅｒｉｚｅｄｂｙａｃｕｔｅｏｒｃｈｒｏｎｉｃｌｉｖｅｒｄｉｓｅａｓｅａｎｄ/ｏｒｎｅｕｒｏｌｏｇｉｃｄｅｆｉｃｉｔｓｄｕｅｔｏｃｏｐｐｅｒａｃｃｕｍｕｌａｔｉｏｎｉｎｌｉｖｅｒａｎｄｂｒａｉｎ Ｔｒｅａｔｍｅｎｔｉｓｔｏｒｅｍｏｖｅｔｈｅｅｘｃｅｓｓｃｏｐｐｅｒｂｙｃｈｅｌａｔｉｎｇａｇｅｎｔｓｓｕｃｈａｓｐｅｎｉｃｉｌｌａｍｉｎｅ1　…     

Analysis of the survival motor neuron and neuronal apoptosis inhibitory protein genes in Malay patients with Spinal Muscular Atrophy

In Malaysia, Spinal Muscular Atrophy (SMA) is diagnosed based on clinical observation with or without muscle biopsy. Molecular analyses of the SMA-related genes have not been available so far. In this preliminary study, we searched for homozygous deletion of Survival Motor Neuron (SMN1) and Neuronal Apoptosis Inhibitory Protein (NAIP) genes in Malay patients with SMA and found homozygous deletion of SMN1 exon 7 and 8 in all the patients while homozygous deletion of NAIP exon 5 was detected in only our type 1 patients but not in the type 3 patient. To the best of our knowledge, these are the first SMA cases diagnosed at the molecular level in Malaysia.     

散发性早发帕金森病parkin基因1、2号外显子突变的研究

【目的】研究parkin基因1、2号外显子突变与散发性早发帕金森病发病的关系。【方法】应用聚合酶链反应（PCR）、琼脂糖凝胶电泳和单链构象多态性（SSCP）方法检测52例散发性早发帕金森病病人外周血白细胞DNA的parkin基因1、2号外显子突变情况,并对SSCP有异常泳动外显子进行DNA测序。【结果】发现1例病人（1.9%）存在parkin基因2号外显子缺失,2例病人（3.8%）分别存在parkin基因1、2号外显子PCR产物SSCP发生泳动变位,测序发现1号外显子为杂合突变（T103C）,2号外显子为纯合突变（G237C）。【结论】parkin基因1、2号外显子突变可能与部分散发性早发帕金森病发病有关。     

Identification of a mutation hotspot in exon 8 of W ilson disease gene by cycle sequencing

Objective To screen for mutation hotspot of Wilson disease (WD) gene in Chinese population.Methods Cycle sequencing was used to detect mutation in exon 8 of WD gene in 30 patients with Wilson disease. Results The same missense mutation, Arg779Leu, was identified in 14 WD patients, four of whom were homozygous and the other heterozygous for this mutation.The frequency of this mutation in Chinese patients was 30%.Conclusion The codon 779 (CCG→CTG) of exon 8 of WD gene was one of mutation hotspots in Chinese.