Spontaneous reversion of novel Lesch-Nyhan mutation byHPRT gene rearrangement

Molecular analysis of an unusual patient with the Lesch-Nyhan syndrome has suggested that the mutation is due to a partial HPRTgene duplication. We now report the cloning and sequencing of the mutant HPRTcDNA which shows the precise duplication of exons 2 and 3. This mutation is the result of an internal duplication of 16–20 kilobases of the gene. The structure of the mutant gene suggests that the duplication was not generated by a single unequal crossing-over event between two normal HPRTalleles. Growth of Epstein-Barr virus-transformed lymphoblasts from this patient in selective medium has permitted isolation of spontaneous HPRT⁺ revertants of this mutation. The reversion event involves a second major HPRTgene rearrangement where most or all of the duplicated portion of the mutant gene is deleted. The original mutation therefore has the potential for spontaneous somatic reversion. This may explain the relatively mild symptoms of the Lesch-Nyhan syndrome exhibited by this patient.     

Toward gene therapy of primary ovarian failure: adenovirus expressing human FSH receptor corrects the Finnish C566T mutation

Resistance ovarian syndrome is a heterogeneous disorder inherited as a Mendelian recessive trait and characterized by infertility, primary amenorrhea, normal karyotype and elevated serum FSH and LH levels. An inactivating mutation, C566T, in FSH receptor gene (FSHR) has been identified initially in Finland. We investigated if an adenovirus expressing a normal copy of human FSHR (Ad-hFSHR) has the ability to: (i) transfect granulosa cell lines, (ii) render the transfected cell lines responsive to FSH stimulation and (iii) transcomplement the malfunctioning form of human FSHR gene with C566T mutation. COS-7, JC-410, JC-410-P450-scc-luc and JC-410-StAR-luc cell lines were infected by Ad-hFSHR followed by treatment with FSH. Functional activity of the Ad-hFSHR was tested by measuring cyclic adenosine monophosphate (cAMP) or luciferase activity in response to FSH stimulation, and showed 2-4.6-fold increases in Ad-hFSHR transfected cells compared with untransfected or Ad-LacZ transfected cells, indicating that Ad-hFSHR is functionally active and expressing hFSHR. Generation of cAMP in cells expressing only mutated hFSHR-T566 showed minimal increase after FSH stimulation. Co-transfection of Ad-hFSHR in these cells carrying the malfunction form of human FSHR caused significant increases of 2.2-7.4-fold in FSH dependent cAMP generation (P = 0.0007). We concluded that adenovirus expressing a normal human FSHR can compensate the inactivating human FSHR-C566T mutation and restore FSH responsiveness.     

True reversion of a mutation in the chloroplast gene encoding the large subunit of ribulosebisphosphate carboxylase/oxygenase in Chlamydomonas

The ribulosebisphosphate carboxylase/oxygenase-defective Chlamydomonas mutant, 10-6C, was the first mutant to be physically defined in chloroplast DNA. In this report, a photosynthesis-competent revertant of the 10-6C mutant has been found to result from true reversion within the chloroplast large-subunit gene. This result supports the original assignment of the 10-6C mutation within the large-subunit gene.     

α1，3半乳糖基转移酶基因721C〉T突变导致Bw亚型

目的研究红细胞ABO血型系统Bw亚型的分子基础. 方法通过标准血型血清学方法明确鉴定2个家庭3例Bw亚型,PCR扩增Bw亚型ABO糖基转移酶基因的增强子、启动子和第1～7外显子及侧翼内含子序列,PCR产物经割胶纯化后直接测序.同时将第6和7外显子克隆到pcDNA3.1(-)质粒,转化DH5α后进行序列分析.采用序列特异性引物-聚合酶链反应方法证实测序所发现的突变.结果直接测序发现3例Bw亚型的基因型为B/O杂合,其中糖基转移酶基因的第261位G杂合缺失,第721位C/T杂合.克隆证实一条染色体上为正常的O等位基因,另一条染色体上B等位基因(α1,3半乳糖基转移酶基因)存在第721位C>T突变,导致多肽链Arg241Trp替换.序列特异性引物-聚合酶链反应检测140份随机样本未发现此突变. 结论α1,3半乳糖基转移酶基因第7外显子721C>T突变可能是Bw亚型分子遗传基础之一.     

白细胞介素-13 基因错义突变rs20541C / T 多态性在广西人群中的分布

目的:分析IL-13 基因rs20541C/ T 位点多态性在广西人群中的分布特点,同时比较其在不同种群之间的分布差异。方法:采用多重单碱基延伸技术(SNaPshot)和DNA 直接测序法对275 例广西人群IL-13 基因rs20541C/ T 进行分型,并分析其基因型及等位基因的分布频率。检测结果与NCBI 中人类基因组国际单体图(HapMap)公布的其他种群(欧洲人、北京人、日本人、非洲人)和文献报道的天津人的基因型及等位基因数据进行比较。结果:IL-13 基因rs20541C/ T 在广西人群中具有多态性,CC、CT 和TT 基因型频率分别为40.0%、46.2%、13.8%,C 和T 等位基因频率分别为63.1%、36.9%。其基因型及等位基因的分布频率在男女性别之间差异无统计学意义(P>0.05),其基因型与欧洲、非洲、天津人群作比较,差异有统计学意义(P<0.05),等位基因分布频率与这5 种人群相比,差异有统计学意义(P<0.05)。结论:IL-13 基因rs20541C/ T 基因多态性在不同种族和地区间存在着不同程度差异。     

Amplification versus mutation as a mechanism for reversion of anHGPRT mutation

We have used a cloned cDNA for hypoxanthine-guanine phosphoribosyltransferase (HGPRT) to analyze the HGPRTgene and mRNA in an HGPRT-deficient mutant of Chinese hamster cells (RJK10) and its HGPRT-positive revertants. By Southern blot analysis, no DNA rearrangements were detected within the genes from any of the cell lines examined. However, four of five spontaneous revertants each contained 10-to 20-fold more copies of the HGPRTgene than did RJK10 or wild-type cells. In contrast, the gene was not amplified in four mutagen-induced revertants. The RJK10 mutation did not alter the size or concentration of HGPRT mRNA and representatives of the revertants contained the mRNA in amounts proportional to the number of genes they carried. Examples of clones with either stable or unstable gene amplification were identified and their HGPRT-positive phenotypes were shown to be dependent on the gene amplification. In a stably amplified revertant, the extra genes were found to be syntenic with the X chromosome marker glucose-6-phosphate dehydrogenase. In an unstable revertant only one of the 10 to 20 copies of the gene could be shown to be X linked. Thus, we found that RJK10 can revert by at least two distinct mechanisms: amplification of the HGPRTgene, which occurred spontaneously, or point mutation, which predominated after exposure to mutagens.     

Spontaneous mutation frequencies in Salmonella: enhancement of G/C to A/T transitions and depression of deletion and frameshift mutation frequencies afforded by anoxic incubation

Incubation of Salmonella typhimurium under anoxic conditions (0.1% oxygen or less) results in a substantial decrease in small (3-and 6-basepair) deletions in an A/T-rich region of the hisG gene in the hisG428 ochre mutant and also decreases the frequency of minus frameshift mutations in G/C-rich sequences in the his-D3052 and hisC3076 mutants. In contrast, the frequency of G/C-----A/T transition mutations increases substantially during anoxic growth of hisG46. Growth of revertants of strains carrying accessory deletions in the uvrB region of the Salmonella chromosome is drastically impaired on glucose minimal medium when oxygen partial pressures are below 0.1% oxygen.     

C1824T mutation in the LMNA gene has no association with senile cataract

Mutations in the LMNA gene encoding lamins A/C are responsible for Hutchinson-Gilford syndrome (HGS), a disorder of premature aging. Cataract is 1 of the main manifestations. The most prevalent mutation in Hutchinson-Gilford syndrome is C1824T, which activates a cryptic splice donor site to produce an abnormal lamin A protein. The purpose of this study was to investigate a possible association of the C1824T mutation with age-related cataract. Anterior lens capsule material was collected during cataract extraction surgery from 178 patients with senile cataract during 2007-2008. DNA and mRNA were extracted and sequenced for the LMNA gene. DNA and cDNA were screened for the C1824T mutation, which was not detected. Messenger RNA (mRNA) expression was normal, with no truncation. We found that human age-related nuclear cataract is not associated with LMNA gene mutations or truncation of lamin A.     

Induced reversion of a spontaneous point mutation within the Chinese hamster HPRT gene to the wild-type sequence.

The Chinese hamster hypoxanthine-guanine phosphoribosyltransferase (HPRT)-deficient cell line TG15 produces apparently normal HPRT mRNA by northern analysis and was therefore presumed to contain a point mutation within the coding region. Sequencing cDNA from the TG15 cell line revealed an A to G transition which results in the substitution of the amino acid glycine for aspartic acid at position 135. TG15 cells revert to wild-type HPRT activity upon exposure to monofunctional alkylating agents. A rapid test to assay the site of the TG15 point mutation has been developed, utilizing the polymerase chain reaction and allele-specific oligonucleotide screening. In all revertants studied, the original point mutation has been corrected to the wild-type sequence. The TG15 point mutation lies within a proposed catalytic domain of the HPRT protein in common with other phosphoribosyltransferases.     

The homozygous C677T mutation in the methylenetetrahydrofolate reductase gene is a genetic risk factor for migraine

Increased homocysteine levels are associated with various pathological conditions in humans, including stroke and cardiovascular disorders. Homocysteine acts as an excitatory amino acid in vivo and may influence the threshold of migraine headache. Frosst et al. [1995] reported an association between the homozygous C677T mutation in the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene and serum homocysteine levels. This study was designed to determine the prevalence of the MTHFR mutation in Japanese patients with migraine and tension-type headache (TH). Seventy-four patients with migraine headaches (22 with aura and 52 without aura), 47 with THs, and 261 normal controls were recruited. Genotyping of MTHFR C677T polymorphism was performed by polymerase chain reaction-restriction fragment length polymorphism. We detected that the incidence of the homozygous transition (T/T) in migraine sufferers (20.3%) was significantly higher than that in controls (9.6%). Moreover, the frequency of the T/T genotype in individuals with migraine headaches with aura was remarkably high (40.9%). The MTHFR T allele was more frequent in the migraine group than in the control group. Our results support the conclusion that the MTHFR gene, causing mild hyperhomocysteinemia may be a genetic risk factor for migraine. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:762-764, 2000.     

C677T mutation in the 5,10-MTHFR gene and risk of Down syndrome in Italy

The C677T polymorphism of the MTHFR gene has been associated to maternal risk of Down syndrome, due to the detection of an higher prevalence of the T allele among mothers of children with trisomy 21, compared to control mothers. In order to confirm this association, we studied the presence of the C677T in 64 mothers of Down syndrome children and 112 controls from central Italy. An higher incidence of the mutant T allele in controls (48.2%) than in Down syndrome children mothers (44%) was detected. These results do not support the presence of an increased risk of Down syndrome in mothers carriers of the T allele in the Italian population.     

A low prevalence of the C677T mutation in the methylenetetrahydrofolate reductase gene in Asian Indians

The prevalence of the C677T mutation in the methylenetetrahydrofolate reductase (MTHFR) gene in Asian Indians from India was determined and the association of the mutant allele with coronary artery disease (CAD) was evaluated in a case-control study. The case group consisted of 251 patients with CAD; 195 male and 56 female aged from 29 to 82 years (mean age +/- SD, 57.5 +/- 10.6 years). The control group consisted of 216 apparently healthy individuals without evidence of CAD; 161 male and 55 female aged from 30 to 83 years (mean age +/- SD, 54.9 +/- 10.4 years). All the patients were assessed by coronary angiography. While 33 patients had normal coronaries, 23, 25 and 39 patients had single-vessel, two-vessel and triple-vessel disease, respectively. Eighty-three patients (33%) had suffered myocardial infarction less than a year to five years earlier. The C677T polymorphism in the MTHFR gene was assessed. While 31% of the controls and 38% of the patients had the heterozygous genotype, 2% of the control group and none of the patients had the mutant homozygous genotype. The overall 'T' allelic frequencies were comparable in control and patient groups (0.18 and 0.19, respectively), but the association of the sum of heterozygous and homozygous genotypes with CAD (1, 2 or 3-vessel disease) was statistically significant for females only [Odds ratio (95% confidence intervals), 2.8 (1.1-6.9), p = 0.023]. No association was found between genotype distribution and previous myocardial infarction or severity of atherosclerosis.     

四引物扩增受阻突变体系分析少精、无精症患者白细胞MLH3基因C2531T突变

目的 分析错配修复蛋白MLH3基因 C2531T 突变与少精、无精症的关系。方法 以MLH3 C2531T为例建立四引物扩增受阻突变体系(4P-ARMS-PCR)方法；分别用4P-ARMS-PCR和PCR-RFLP检测81例少精、无精症患者和80例正常对照者MLH3 C2531T；随机抽取20%标本测序进行验证。结果 MLH3 C2531T CT+TT基因型在患者中有明显的流行，且MLH3 C2531T T等位基因与疾病存在相关性(P＜0.01);PCR-RFLP检测结果与4P-ARMS-PCR检测结果完全一致，测序结果相同。结论 4P- ARMS-PCR可快速、简便、准确检测基因单核苷酸突变(SNP); 错配修复蛋白MLH3 C2531T多态性与少精、无精症存在相关性。     

Maternally inherited deafness associated with a T1095C mutation in the mDNA

Hearing loss is a relatively frequent defect in children with a genetic or predisposition basis in about 50% of cases. Mitochondrial DNA (mtDNA)-associated disorder often present with sensorineural hearing loss (SNHL) either in isolation or as a part of a multisystem disorder in adults but the frequency in pediatric cases is unknown. We analysed deafness-related mtDNA mutations in 80 deaf children to assess the relative frequency of alterations in childhood-onset SNHL. In 16 patients in whom maternal inheritance was possible, we screened for new mutations likely to affect mitochondrial protein synthesis. In one child we detected a novel mutation (T1095C) in the 12S rRNA gene. This mutation fulfils the suggested criteria for definition of a disease-related nucleotide variant. No mutations were found in other patients. Although we cannot exclude the presence of still undefined new mtDNA mutations, our data suggest that mtDNA defect are not common in childhood-onset SNHL.     

Spontaneous mutation spectrum in the hprt gene in human lymphoblastoid TK6 cells

A spectrum of 100 mutations in the endogenous hprt gene of thehuman lymphoblastoid TK6 cell line is presented. The majorityof the mutations originates in sequences outside the codingregion of the gene. Large deletions are a major cause of inactivationof the hprt gene (57% of the mutants). Mutations in the splicesites that result in several forms of aberrantly spliced mRNAare relatively frequently recovered (16%) compared with mutantscontaining alterations in the coding region of the hprt gene(27%). The majority, but not all, of the splice mutants containan alteration in the consensus sequences of the splice sites.A spectrum of mutations in the coding region of the hprt geneenlarged to a total of 42 mutants shows that basepair substitutionspredominate (71%) and that small deletions and insertions areless frequently recovered. Basepair substitutions arise slightlymore frequently at GC basepairs than at AT basepairs. ³To whom correspondence should be addressed     

Efficient adenovirus-mediated gene transfer into primary T cells and thymocytes in a new coxsackie/adenovirus receptor transgenic model

Background  

Gene transfer studies in primary T cells have suffered from the limitations of conventional viral transduction or transfection techniques. Replication-defective adenoviral vectors are an attractive alternative for gene delivery. However, naive lymphocytes are not readily susceptible to infection with adenoviruses due to insufficient expression of the coxsackie/adenovirus receptor.     

The C677T mutation in the methylene tetrahydrofolate reductase gene increases serum uric acid in elderly men

A common mutation, C677T, in the methylene tetrahydrofolate reductase gene (MTHFR) reduces the activity of MTHFR and increases total homocysteine levels in plasma. Increased homocysteine levels are reportedly associated with high serum uric acid levels. The relationship between the MTHFR mutation and uric acid metabolism remains unclear, however. To investigate whether the C677T MTHFR mutation is a risk factor for hyperuricemia, we performed MTHFR genotyping and clinical laboratory determinations, including serum uric acid, in 271 elderly Japanese men (age range, 40–79 years; mean, 52.6 years). The mean uric acid levels for the C/C, C/T, and T/T genotypes were 5.67, 6.00, and 6.39 mg/dl, respectively (P = 0.012). The T/T genotype was more frequent in subjects with high uric acid levels than in those with low uric acid levels (P = 0.038). These findings suggest that the C677T MTHFR mutation contributed to higher uric acid levels in subjects enrolled in this study. In conclusion, the mutation of the MTHFR gene may be a risk factor for hyperuricemia in elderly men. Received: February 28, 2000 / Accepted: February 29, 2000     

Two novel mutations and coexistence of the 991C.T and the 1339C.T mutation on a single allele in the coproporphyrinogen oxidase gene in Swedish patients with hereditary coproporphyria

 Hereditary coproporphyria (HCP) is an autosomal dominant disorder, resulting from a partial deficiency of the enzyme coproporphyrinogen oxidase (CPO). This enzyme catalyzes the sixth step of the heme biosynthetic pathway, and mutations in the CPO gene have been coupled to HCP. The present study was undertaken to identify disease-producing mutations in the CPO gene in nine Swedish families with HCP. Exon 1 of the CPO gene of the nine probands was analyzed directly by sequencing, and exons 2–7 were screened by denaturating gradient gel electrophoresis, followed by sequencing of exons showing abnormal band pattern. Mutations were detected in five of the nine families. In two of these families, the novel mutations 623C>T (S208F, exon 2) and 982C>T (R328C, exon 5) were identified, respectively. In the affected members of the other three families, the previously reported mutations 991C>T (R331W, exon 5) and 1339C>T (R447C, exon 7) were shown to coexist on one allele. The present study contributes 2 novel mutations to the 34 that have been previously reported to cause HCP. In addition, this is the first report on patients carrying two HCP-coupled mutations on one allele. Received: March 8, 2002 / Accepted: April 24, 2002