Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Point Mutation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 253 records · Page 14Linked to original sources
PubMed1994

Double- and single-strand conformation polymorphism analysis of point mutations and short tandem repeats.

Single point mutations in small DNA fragments and single unit differences in simple repetitive DNA can be detected as double-strand conformation polymorphisms using polyacrylamide gel electrophoresis, with and without sodium dodecyl sulfate, even at temperatures as low as 3 degrees C. Changes in a single base are distinguished by means of the analysis of the heteroduplexes, and changes in more than two bases can be distinguished in both homoduplexes and heteroduplexes. Polymerase chain reaction (PCR) conditions can be designed not only to amplify homoduplexes, heteroduplexes and single-strand DNA at the same time, but also to focus the analysis on either single-strand conformation polymorphism (SSCP) or double-strand conformation polymorphism (DSCP). DSCP seems to be advantageous in typing DNA polymorphisms or mutations in loci with few variants, but, because it is necessary to have a simple pattern of all possible combinations of the alleles, it is not as advantageous in typing systems with many variants.

Base Sequence↗
PubMed1994

The Neurospora transposon Tad is sensitive to repeat-induced point mutation (RIP).

RIP (repeat-induced point mutation) efficiently mutates repeated sequences in the sexual phase of the Neurospora crassa life cycle. Nevertheless, an active LINE-like retrotransposon, Tad, was found in a N. crassa strain from Adiopodoumé. The possibility was tested that Tad might be resistant to RIP, or that the Adiopodoumé strain might be incompetent for RIP. Tad elements derived from the Adiopodoumé strain were found to be susceptible to RIP. In addition, strains lacking active Tad elements, including common laboratory strains and strains representing seven species of Neurospora, were found to have sequences closely related to Tad but with numerous mutations of the type resulting from RIP (G:C to A:T). Even the Adiopodoumé strain showed Tad-like elements with mutations characteristic of RIP. Results of crossing of an Adiopodoumé transformant with progeny of Adiopodoumé suggest that the Adiopodoumé strain is proficient at RIP. We conclude that Tad is an old transposable element that has been inactivated by RIP in most strains. Finding relics of RIP in both heterothallic and homothallic species of Neurospora implicates RIP across the genus.

Base Sequence↗
PubMed2001

Antithrombin deficiency in Brazilian patients with venous thrombosis: molecular characterization of a single splice site mutation, an insertion and a de novo point mutation.

The prevalence of antithrombin (AT) deficiency in 342 unselected Brazilian patients with venous thrombosis was 1.16%, which increased to 3% when only patients under the age of 50 or with a familial history of thrombosis were considered. In two patients, a clinical (contraceptive use) or genetic risk factor (factor V Leiden and C677T in the methylene tetrahydrofolate reductase gene [MTHFR]) was identified and corroborated the hypothesis that an interaction of factors accounted for the appearance of thrombosis. However, no risk factor other than AT deficiency was identified in one patient with an important clinical and family history of spontaneous thrombosis. Three mutations were identified in these patients: a G-->A transition in intron 5 at position +1 (5'-->3'), three base insertions corresponding to arginine at position 5383 in exon 3A, and a G-->A transition at 13328, corresponding to an Ala404Thr de novo mutation. The polymorphisms in the genes coding for coagulation factors XII and XIII and fibrinogen normally associated with an increased risk for venous thrombosis were not related to thrombosis in these patients. This is the first study in South America to assess the prevalence of AT deficiency and to report the molecular characterization of the mutations involved.

Adult↗
PubMed1995

No point mutation but decreased expression of the p16/MTS1 tumor suppressor gene in nasopharyngeal carcinomas.

Nasopharyngeal carcinoma (NPC) is a malignancy which occurs at high incidence in southern China and southeast Asia. The molecular mechanism of this disease, however, is not well understood. Recently, a homozygous deletion and/or loss of heterozygosity on chromosome 9p21-22 was found in several primary NPCs (Huang et al., Cancer Res. 54: 4003-4006, 1994), suggesting that a potential tumor suppressor gene(s) residing in this region may play a role in nasopharyngeal carcinogenesis. Since p16/MTS1, a potential tumor suppressor gene, whose mutations/deletions are frequently found in variety of tumor cells, was mapped to chromosome 9p21, we investigated the possible involvement of this gene in the development of NPC by mutational and Northern blot analysis. SSCP-direct sequencing revealed no point mutations of the p16/MTS-1 gene in any of 42 primary NPC biopsies from three geographical regions nor in two NPC cell lines. We did, however, observe a codon 140ala-->thr polymorphism in the gene, which has been previously reported as a point mutation. Furthermore, Northern analysis revealed a decreased expression of the p16/MTS1 gene in two out of two NPC cell lines as compared with immortalized/nontransformed cell lines. These results suggest that down regulation rather than a point mutation of the p16/MTS1 gene may play a role in the genesis of NPC.

Base Sequence↗
PubMed1993

Evidence for a recessive PMP22 point mutation in Charcot-Marie-Tooth disease type 1A.

Charcot-Marie-Tooth disease type 1A (CMT1A) is an autosomal dominant neuropathy that can be caused by dominant point mutations in PMP22 which encodes a peripheral nerve myelin protein. Usually, CMT1A is caused by the duplication of a 1.5-megabase (Mb) region on chromosome 17p11.2-p12 containing PMP22. Deletion of a similar 1.5-Mb region is associated with hereditary neuropathy with liability to pressure palsies (HNPP), a clinically distinct neuropathy. We have identified a severely affected CMT1 patient who is a compound heterozygote for a recessive PMP22 point mutation, and a 1.5 Mb deletion in 17p11.2-p12. A son heterozygous for the PMP22 point mutation had no signs of neuropathy, while two others heterozygous for the deletion had HNPP, suggesting that point mutations in PMP22 can result in dominant and recessive alleles contributing to CMT1A.

Aged↗
PubMed1994

Relation between the occurrence of K-ras gene point mutations and genotypes of polymorphic N-acetyltransferase in human colorectal carcinomas.

We examined the point mutations of codons 12, 13 and 61 in K-ras gene by slot blot hybridization analysis following polymerase chain reaction and genotypes of polymorphic N-acetyltransferase (NAT) by Southern blot analysis in 36 colorectal carcinoma tissues obtained at surgery. NAT genotypes of 36 autopsied livers from patients without colorectal carcinoma were also determined to compare the populations of each polymorphic NAT genotype in the patients with or without the neoplasm. Genetically, 44.4% (16 cases), 47.2% (17 cases) and 8.3% (3 cases) of patients with colorectal carcinoma were classified as rapid, intermediate and slow acetylators, respectively. Point mutations of K-ras gene were detected in eight carcinomas out of 16 rapid acetylators, two out of 17 intermediate acetylators and one out of three slow acetylators. In control livers, 52.8% (19 cases), 38.9% (14 cases) and 8.3% (3 cases) were classified as rapid, intermediate and slow acetylators, respectively. The occurrence of K-ras gene point mutations was closely linked to rapid acetylator genotype, although there was no statistical difference of NAT genotypes between the group of patients with colorectal carcinoma and the group of controls.

Adult↗
PubMed2001

[A rapid and simple detection of DNA fragment with point mutation by capillary electrophoresis].

OBJECTIVE: To establish a rapid and simple method with high efficiency in detecting point mutation of genomic DNA. METHODS: Four DNA fragments that were different from each other in only one based were amplified by using primers with artificial point mutation based on the sequence of exon 7 of p53 gene, and then were separated by capillary electrophoresis(CE). The neutral coated capillary and 4% linear polyacrylamide gel buffer were used, and the wave length of ultraviolet detector was 254 nm. RESULTS: A homozygous 196 bp DNA fragment can be separated into one dsDNA peak and two ssDNA peaks within 25 minutes, and the heterozygous 196 bp DNA fragments that were made with mixed wild type and mutated DNA can be separated into one dsDNA peak and three ssDNA peaks. The three ssDNA fragments that differ in one nucleotide can be easily separated with good resolution. CONCLUSION: CE technique is rapid, sensitive, accurate and well reproducible. It is an efficient and reliable method for rapidly screening point mutation.

Base Sequence↗
PubMed2004

K-ras gene point mutations and p21ras immunostaining in human ovarian tumors.

It is well recognized that genetic alterations within oncogenes, tumor suppressor genes, DNA mismatch repair and excision repair genes contribute to tumorigenesis within the human ovary. This study was undertaken to screen for the existence of K-ras gene point mutations in paraffin-embedded slides randomly selected from benign and malignant ovarian tumors applying the PCR-RFLP technique. Expression of p21ras was also assessed in 30 primary ovarian adenocarcinomas immunohistochemically. K-ras codon 12 point mutations occurred in nine of 40 (22.5%) cases. They were not identified in two benign mucinous cystadenomas, but in one out of two (50%) mucinous tumors of LMP (low malignant potential), in five out of 30 (17%) ovarian adenocarcinomas, and in one case of adenocarcinoma metastatic to the ovary. K-ras activation was also detected in one out of four (25%) sex cord-stromal cell tumors (folliculoma), and in one dysgerminoma. None of these tumors exhibited K-ras codon 13 point mutations. Gene alterations were more frequently found in mucinous than in non-mucinous (30% vs 10%) tumors, although the difference did not reach significance (p > 0.05). The frequency of K-ras point mutations was correlated neither with clinical nor with pathological variables of cancer. Cytoplasmic p21ras was expressed in all adenocarcinomas negative for K-ras point mutations, whereas one of five (20%) K-ras-positive tumors exhibited lack of immunoreactivity. In conclusion, these findings confirm the role of K-ras activation in mucinous ovarian tumors. p21ras expression is not necessarily associated with K-ras gene alterations in human ovarian adenocarcinomas.

Adenocarcinoma↗
PubMed2005

Molecular prevalence of point mutations conferring resistance to clarithromycin in Helicobacter pylori in the United Arab Emirates.

OBJECTIVE: The aim of the study was to find the prevalence of point mutations conferring resistance to clarithromycin in Helicobacter pylori (H. pylori) in the United Arab Emirates. METHODS: Gastric biopsy samples were obtained from 9 dyspeptic patients attending the endoscopy department in Zayed Military Hospital, Abu-Dhabi, UAE during the period from January to September 2004. Real-time polymerase chain reaction (PCR) was carried out for these biopsies to determine the point mutations. RESULTS: Of the 55 (60%) real-time biopsies that were PCR positive for H. pylori, 36 (65.5%) were found to have mutant genes. The A(2142/43)G mutation was more common (63.6%) than the A(2142)C mutation (18.2%). CONCLUSION: Point mutations A(2442/43)G and A(2142)C and the combination of both were common among our patients. Perhaps the highest reported yet. Mutation at A(2142/43)G is far more common than mutation at A(2142)C.

Anti-Bacterial Agents↗
PubMed2003

Exposure to chronic, low-dose rate gamma-radiation at Chornobyl does not induce point mutations in Big Blue mice.

Empirical genetic effects resulting from low-dose rate irradiation and chronic, cumulative exposure are poorly characterized. Expected effects are based on epidemiological studies and downward, linear extrapolations from nonthreshold models derived from acute, high-dose exposures. These extrapolations and their associated risk coefficients have no experimental support, and because of their inherent uncertainty they are the subject of considerable debate. The expectation of deleterious genetic effects resulting from low-dose rate irradiation and chronic exposure is in need of empirical assessment because this type of exposure is typical of those encountered in occupational, residential, and environmental settings. Recent acute low-dose (<10 cGy) studies using cytogenetic and point mutation endpoints indicate that observed effects range from those lower than spontaneous to an increase in the frequency of point mutations. Using the Big Blue assay, we examined the ability of chronic, continuous gamma-irradiation (2.3 x 10(-3) cGy/min) in the Chornobyl environment to induce point mutations. This system has demonstrated a significant point mutation sensitivity (4.5-fold increase) to acute, high-dose (1-3 Gy) gamma-radiation. Mutant frequencies and the mutation spectra were examined in exposed and reference samples of Big Blue mice following 90 days exposure (cumulative absorbed dose = 3 Gy) to the Chornobyl environment. No significant increase in the mutant frequency or bias in the mutational spectrum was observed in exposed individuals. This finding suggests that low-dose rate gamma-irradiation at Chornobyl does not induce point mutations and that cumulative, chronically absorbed doses do not induce the same genetic effects as acute doses of the same magnitude.

Animals↗
PubMed1995

[p53 gene point mutation in human colorectal carcinoma].

We introduced two modified assay systems, PCR-SSCP and PCR-direct sequencing for the identification of structure aberration at p53 exon 7 in 22 colorectal carcinomas and 1 metastatic lymph node. The data indicated that 27.2% (6/22) colorectal carcinomas and one metastatic lymph node were shown to contain the point mutations in codons 245, 251, 259 and 260 of exon 7. One half of all the mutations was G:c to A:T transition in codon 245. Other mutation patterns were base insertion and deletion. All positive point mutations of p53 exon 7 existed in colon carcinomas in this study. The point mutation in p53 exon 7 was usually associated with poorly differentiated primary carcinomas (P = 0.0178) and the mutation rate of was higher in Duckes C stage of the disease than in stage Duckes A and B (P = 0.0361). Thus p53 exon 7 point mutation in primary colorectal tumors and regional lymph nodes may identity a subgroup of colorectal cancer patients with more aggressive disease and may be as a new tumor markers for assessing the prognosis of colorectal carcinomas.

Adult↗
PubMed1991

Effect of an adjacent base on detection of a point mutation by restriction enzyme digestion.

While routinely mapping point mutations within the arginase locus of a collection of hyperargininemic patients, we discovered that a base immediately outside a restriction endonuclease recognition site (TaqI) can eliminate cleavage of this site by this enzyme. The genetic lesion lay in a base immediately flanking a TaqI recognition site within exon 8 of the arginase locus and abolished cutting by approximately 80%. We wish to emphasize the necessity of heeding subtle cues frequently encountered while generating restriction enzyme data, because neither Southern blot maps nor endonuclease digestion of polymerase chain reaction amplified products of exon 8 accurately predicted where the point mutation lay. To our knowledge, this is the first instance of inhibition of cleavage by flanking bases occurring on natural (nonsynthetic) DNA substrates, i.e., within the clinical setting of characterization of a human genetic disorder.

Base Sequence↗
PubMed1997

Fiberoptic DNA sensor array capable of detecting point mutations.

The first integrated fiberoptic DNA sensor array capable of simultaneously monitoring multiple hybridization events has been prepared. In this study, 5'-amino-terminal DNA probes were covalently immobilized by reaction with succinimidyl ester residues in acrylamide-based polymer matrices. DNA sensor arrays of three different oligonucleotide probes, p(dA)(18-mer), H-ras wild-type (10-mer), and H-ras mutant (11-mer) were fabricated, and real-time hybridization of 5'-fluorescein isothiocyanate (FITC)-labeled target oligonucleotides to the array was monitored. H-ras wild-type and Eta-ras mutant differ by a one-base substitution (point mutation) and were used to demonstrate the sensor's ability to distinguish point mutations. Thermal studies indicated a 13 degrees C decrease in the Tm of a duplex with a single-base mismatch. The fiberoptic DNA sensor array was used to discriminate a point mutation by monitoring the real-time hybridization of FITC-labeled target oligonucleotides at 54 degrees C and detected labeled-target oligonucleotides in the range 0.2-196 nM. The lower detection limit is approximately an order of magnitude lower than previously reported DNA biosensors. The DNA sensor array was used to positively identify a point mutation of a biotin-primer-labeled (109 bp) PCR product of the H-ras oncogene. The unitary fiberoptic sensor array is highly sensitive, has the ability to determine point mutations, and has the potential to sample submicroliter volumes due to the small volumes of the individual array elements (20 pL).

Biosensing Techniques↗
PubMed1993

Unbiased analysis of the frequency of beta-thalassemia point mutations in a population of African-American newborns.

OBJECTIVE: To determine frequency of specific beta-thalassemia alleles in the African-American population prospectively, using newborn screening specimens, and to evaluate the need for including these alleles in screening follow-up programs. DESIGN: Allele-specific oligonucleotide tests were developed and used to analyze African-American newborn screening specimens for beta-thalassemia point mutations to determine their frequency. Direct sequencing of amplified DNA from the dried blood specimens was used to confirm the presence of point mutations. POPULATION: African-American newborns in Texas. RESULTS: Allele-specific oligonucleotides identified five newborn specimens carrying beta-thalassemia point mutations among 471 specimens from African-American neonates. Direct sequencing of DNA from the dried blood specimens confirmed that these individuals had a normal and a mutant allele. Five newborn screening specimens in which the results of screening and DNA tests were in disagreement (four with FS by screening and AS by DNA, and one with FC by screening and AC by DNA) were analyzed for these beta-thalassemia point mutations and in each case were found to be S/beta-thalassemia or C/beta-thalassemia compound heterozygotes, respectively. CONCLUSIONS: Allele-specific oligonucleotides accurately identified newborn specimens carrying beta-thalassemia point mutations. Direct sequencing from dried blood specimens confirmed these results. The A(-29)G allele frequency was 0.003, and the C(-88)T frequency was 0.002. These alleles also were observed among positive samples in a neonatal hemoglobinopathy screening program. Therefore, any newborn screening program with a molecular genetic follow-up component must include testing for these beta-thalassemia alleles to assure timely and appropriate management for affected infants.

Alleles↗
PubMed2005

[The point mutations in Pfcrt and Pfmdr1 genes in Plasmodium falciparum isolated from Hainan Province].

OBJECTIVE: To evaluate the point mutations in Pfcrt and Pfmdr1 genes in Plasmodium falciparum isolated from Hainan Province. METHODS: Nested polymerase chain reaction and restriction fragment length polymorphism were used to detect the point mutations at codon 76 of Pfcrt and at codon 86, 1246 of Pfmdr1 in P. falciparum isolates. Chloroquine resistance was measured by the in vitro microtest recommended by WHO. RESULTS: In 36 samples tested, 28 were successfully amplified for Pfcrt, 64.3% of them carried mutant allele at codon 76, 21.4% with wild allele K76 and 14.3% with mixed allele mutation. While for Pfmdr1, 3.4% isolates displayed the 86Y mutation, 89.7% with wild allele N86 and 6.9% with the mixed alleles in 29 isolates which were amplified successfully for N86Y. No point mutation in Pfmdr1 at codon 1246 was found in 13 isolates from the total 36 samples. By the in vitro test, 72.2% (26/36) showed resistance to chloroquine. The 76T and 86Y mutant alleles were present in both in vitro susceptible and resistant isolates. There was a significant difference between susceptible and resistant isolates carrying 76T mutant codon (P < 0.05), but no significant difference was found in Pfmdr1 (P < 0.05). CONCLUSION: There is a significant difference of the 76T prevalence in Pfcrt gene between the susceptible isolate and resistant one of P. falciparum to chloroquine in vitro. The Pfcrt 76T may be used as a predictive marker for chloroquine resistance surveillance.

Adolescent↗
PubMed2004

High sensitive approach for point mutation detection based on electrochemiluminescence.

An electrochemiluminescence-polymerase chain reaction (ECL-PCR) method for point mutation detection has been developed. The target is amplified using a tris (bipyridine) ruthenium (TBR)-labeled forward and a biotinylated reverse primer. The amplification products are digested with specific restriction enzyme, then captured onto streptavidin-coated paramagnetic beads, and detected by measuring the ECL signal of the TBR label. The established technique was further applied to detect a specific point mutation in H-ras oncogene in T24 cell line. The results show that the system has a low detection limit of 100 fmol and a linear range of more than 3 orders of magnitude for H-ras amplicon; the two genotypes can be reliably discriminated. In summary, the mutant specific ECL-PCR method can be used to detect a point mutation that creates or destroys a restriction site in any gene. It is useful in single nucleotide polymorphism (SNP) and mutation detection due to its safety, high sensitivity and simplicity.

Biomarkers, Tumor↗
PubMed1998

Detection of K-ras point mutations in the supernatants of peritoneal and pleural effusions for diagnosis complementary to cytologic examination.

To determine whether DNA analysis can be performed using the supernatants of body fluids after centrifugation at 2,000 rpm for 10 minutes, peritoneal or pleural effusions or bile were examined for K-ras mutations in 34 cases of pancreatic, colorectal, gastric, esophageal, or hepatocellular carcinoma and 15 noncancer cases. The polymerase chain reaction products for K-ras gene codons 2 to 97 of exons 1 and 2 were generated with 41 (93%) of 44 body cavity fluid and 5 (100%) of 5 bile samples. By the single strand conformation polymorphism method, point mutations were detected in the ascites supernatants of 8 (89%) of 9 cases of pancreatic carcinoma. In the remaining case, no point mutation was demonstrated because few malignant cells were present in the ascites fluid. Furthermore, K-ras point mutations were observed in the ascites supernatants of 2 cases of colorectal carcinoma and 1 case of gastric carcinoma. The DNA analysis of the supernatant of ascites fluid showed a K-ras point mutation in 3 cases of false-negative cytologic diagnosis (2 cases of pancreatic carcinoma and 1 case of colorectal carcinoma). Direct sequencing confirmed identical point mutations in the supernatants, whole cell pellets, malignant cells from the cytologic smears of ascites fluid, and cancer tissues. This novel method allows simultaneous testing for genetic abnormalities in supernatants of body fluid, after removing cells for cytologic diagnosis.

Ascitic Fluid↗
PubMed2001

Point mutation and polymorphism in Duchenne/Becker muscular dystrophy (D/BMD) patients.

Duchenne and Becker muscular dystrophies (D/BMD) are caused by mutations in the dystrophin gene. Two-thirds of patients have large intragenic deletions or duplications and the remaining one-third have point mutations, small deletions or insertions. Point mutations are more difficult to detect due to the enormous size (2.4 Mb) of the gene and its large transcript (14 kb). In the present study, a total of 50 DNA samples from unrelated D/BMD (38 DMD and 12 BMD) patients who did not show intragenic deletions by multiplex PCR, were analyzed for detection of point mutations. Single stranded conformation analysis and heteroduplex analysis observed electrophoretic mobility shifts in one (BMD) and two (DMD and BMD) patients, respectively. The mobility shift and heteroduplexes were observed in exon 17 in all of the three patients. Sequencing of the amplified PCR products revealed a nucleotide change (-37 g to t) in the intronic region in two of the patients while a C2268T substitution in the exonic region in one. Mutation database search for D/BMD mutations showed the nucleotide substitution in the exonic region as a novel change in the human dystrophin gene, which was not reported earlier. It resulted in an amino acid transition from threonine to methionine in the 687th position of the dystrophin protein. This novel substitution has been included in the mutation database of Leiden muscular dystrophy pages (http://www.dmd.nl) in the rare polymorphism/mutation category. The substituted nucleotide segregated with the disease phenotype in the family suggesting that it can be directly used for carrier detection and prenatal diagnosis without identification of disease causing mutation.

Amino Acid Sequence↗