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PubMed1991

Differential activation of ras genes by point mutation in human colon cancer with metastases to either lung or liver.

To study the possible role of ras oncogene activation in the dissemination of colon cancer, we determined point mutations in codons 12, 13 and 61 in K- and N-ras in 3 groups of tumors: (A) primary tumors of patients who had undergone surgery for Dukes' B (early-stage) colon cancer, (B) primary tumors and metastases from patients undergoing resection of isolated lung metastases and (C) primary tumors and metastases from patients undergoing resection of isolated liver metastases. In 129 samples from 93 patients, 54 (42%) were positive for point mutations in either K- or N-ras. Most mutations (89%) were found in the K-ras gene. In group A (n = 50) ras point mutations were detected in 16 cases (32%) (15 in K-ras and 1 in N-ras). Thirteen out of 23 cases in group B (57%) were positive for a ras point mutation: 10 in K-ras and 3 in N-ras. In group C (n = 20), point mutations in codon 12 of K-ras, but none in H- or N-ras, were found in 10 cases (50%). In 31 cases the primary tumors from the metastases in groups B and C were available for analysis and 15 contained a ras point mutation (48%). Not all mutations were present in both the primary tumor and the metastasis. In 3 instances, a mutation was detected in the metastasis but not in the primary tumor, whereas in 1 case a mutation was found in the primary tumor.

Adenocarcinoma↗
PubMed1993

Phenotypic heterogeneity in families with the myoclonic epilepsy and ragged-red fiber disease point mutation in mitochondrial DNA.

Two families with a point mutation in mtDNA associated with myoclonic epilepsy and ragged-red fiber disease showed pronounced clinical heterogeneity. The mothers of the two families had adult-onset myopathy with ragged-red fibers, partial deficiency of cytochrome c oxidase, and sensory neuropathy. Members of the first family had variable clinical features of progressive ataxic-myoclonic encephalomyopathy and of the other family, primarily adult-onset myopathy. There was a point mutation from A to G at nucleotide pair 8344 located in the tRNALys gene of the mtDNA of all patients tested, three in Family 1, and the mother of Family 2. This clinical heterogeneity may reflect the effects of varying proportions of mutant and wild-type mtDNA in the different organ systems in each individual.

Adenine↗
PubMed1997

Double-gradient DGGE for optimized detection of DNA point mutations.

A novel technique is reported for screening point mutations is genomic DNA: double gradient, denaturing gradient gel electrophoresis (DG-DGGE). Unlike conventional DGGE, which exploits a single gradient of denaturing chemicals (typically urea and formamide) along the migration path to force the two hetero- and two homo-duplexes to partially unwind and separate, DG-DGGE superimposes a second (porous) gradient over the denaturing one. With the help of the sieving gradient, molecules such as the hetero-duplexes, which often produce curtains and smears instead of sharp zones, due to lack of a sharp melting transition, are re-compacted into remarkably narrow bands. Even homo-duplexes with minute melting temperature differences, giving a single band in DGGE, are resolved into two zones in DG-DGGE. The technique has been applied to the analysis of a number of point mutations in several exons of the cystic fibrosis transmembrane conductance regulator gene.

Cystic Fibrosis↗
PubMed1983

Point mutations in the regulatory region of the human adenoviral VAI gene.

The VA RNA genes of human adenoviruses are transcribed by RNA polymerase III and, like other RNA polymerase III transcriptional units, contain internal regulatory regions. By means of a scheme for directed mutagenesis which employs a deletion mutation to define the target, point mutations have been induced in the regulatory region of a cloned VAI gene. One mutant plasmid which fails to direct VAI transcription and several others which direct the synthesis of normal amounts of RNA of aberrant electrophoretic mobilities were identified using an in vitro transcription assay. The nucleotide sequences of the regulatory regions of three of these plasmids have been determined. All three contain mutations which fall in a block of nucleotides whose sequence (GGTTCGANNCC) is highly conserved in RNA polymerase III promoters (Galli, G., Hofstetter, H., and Birnstiel, M. L. (1981) Nature (Lond.) 294, 626-631). The VAI-negative mutant (pRR5028) contains a G leads to A transition mutation at the second position, which is invariant in functional RNA polymerase III promoters. One mobility variant carries three point mutations, including one G leads to A base change at the position adjacent on the 5' side to that altered in pRR5028. The third mutant contains a single C leads to T transition mutation, in the final position of the conserved block.

Adenoviruses, Human↗
PubMed2000

Analysis of point mutation in exon 2 of CYP2E1 gene in renal cell/urothelial cancer patients in comparison with control population.

OBJECTIVE: Genetic polymorphisms of human cytochrome P450s have been implicated to be of importance for susceptibility to different cancers. Recently, a point mutation was found in the exon 2 of the CYP2E1 gene (CYP2E1*2) [Hu et al. 1997]. In order to evaluate a possible link between the point mutation in exon 2 of the CYP2E1 gene and the susceptibility to renal cell/urothelial cancer, we developed a screening method based on the polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP). MATERIAL: DNA of peripheral white blood cells was isolated from 158 renal cell/urothelial cancer patients as well as from 150 controls. METHOD: Primers for PCR were designed by the Primer 3 release 0.1 program. The PCR yield a product of 215 base pairs (bp), which was digested with the restriction enzyme Hha I. The DNA fragments were separated on a 3% agarose gel stained with ethidium bromide. Restriction enzyme digestion of the PCR product obtained from the wild-type DNA resulted in the appearance of a 66 bp, a 43 bp, a 40 bp, a 39 bp and a 28 bp DNA fragment. In contrast to the wild-type, the digestion of the PCR product from DNA carrying the point mutation resulted in the loss of the 39 bp and 40 bp fragments and the appearance of an additional 79 bp fragment. Therefore, the loss of one Hha I restriction site caused by a single nucleotide exchange is suitable for the identification of the point mutation in exon 2 of CYP2E1 gene. RESULTS: However, we could not detect any point mutation in any of the 158 renal cell/urothelial cancer patients or the 150 controls. The distribution of the point mutation in exon 2 of CYP2E1 gene did not show any difference in renal cell/urothelial cancer patients and controls. CONCLUSION: This might indicate a lack of association between this CYP2E polymorphism (CYP2E1*2) and renal cell/urothelial cancer.

Base Sequence↗
PubMed1990

Detection of point mutations in type I collagen by RNase digestion of RNA/RNA hybrids.

We have developed a strategy for the detection, localization and sequence determination of point mutations in the mRNA coding for the alpha 1(I) and alpha 2(I) chains of type I collagen. Point mutations are detected by RNase A cleavage of mismatches in RNA/RNA hybrids. The mRNAs coding for the fibrillar collagens present special problems for hybrid analysis because of their large size and their GC-rich and repetitive sequences. We have generated a series of overlapping antisense riboprobes covering the entire pro alpha 1(I) and pro alpha 2(I) mRNAs. Uniformly labelled normal antisense riboprobes are hybridized with the total fibroblast RNA of patients with possible mutations in type I collagen. Mismatches in the resulting RNA/RNA hybrids are cleaved with RNase A and the labelled riboprobe cleavage products are examined electrophoretically. The sensitivity and specificity of the system were demonstrated by the detection and localization of a known point mutation in the codon for alpha 1(I) glycine 988 (1). DNA for sequencing the mutations localized by hybrid analysis may be obtained by either (1) generation of a fibroblast cDNA library and isolation of both alleles by plaque screening, or (2) a more rapid method using first strand cDNA synthesis from poly (A+)-mRNA, followed by PCR amplification of the mutation-containing region of the DNA/RNA hybrid. This strategy for detection and isolation has wide application not only for mutations causing connective tissue disorders, but also for mutations in other large and repetitive genes. We have used this strategy for the detection and sequencing of a point mutation in alpha 2(I) mRNA associated with a case of lethal osteogenesis imperfecta. The G----A point mutation in the codon for alpha 2(I) glycine residue 805 results in the substitution of an aspartic acid at this position and is consistent with the proband's collagen protein data.

Alleles↗
PubMed2002

Ageing muscle: clonal expansions of mitochondrial DNA point mutations and deletions cause focal impairment of mitochondrial function.

Although mitochondrial DNA deletions have been shown to accumulate in cytochrome c oxidase deficient muscle fibres of ageing muscle, this has not been demonstrated for point mutations. In this study, we investigated the occurrence of mitochondrial DNA alterations (point mutations and deletions) in cytochrome c oxidase deficient muscle fibres from 14 individuals, without muscle disease, aged 69-82 years. Immunohistochemical investigation showed that the majority of the cytochrome c oxidase deficient muscle fibres expressed reduced levels of subunit II of cytochrome c oxidase, which is encoded by mitochondrial DNA, whereas there was normal or increased expression of subunit IV of cytochrome c oxidase, which is encoded by nuclear DNA. This pattern is typical for mitochondrial DNA mutations causing impaired mitochondrial translation. Single muscle fibres (109 cytochrome c oxidase deficient and 109 normal fibres) were dissected and their DNA extracted. Mitochondrial DNA point mutations were searched for in five tRNA genes by denaturing gradient gel electrophoresis while deletions were looked for by polymerase chain reaction amplification. High levels of clonally expanded point mutations were identified in eight cytochrome c oxidase deficient fibres but in none of the normal ones. They included the previously described pathogenic tRNALeu(UUR)A3243G and tRNALysA8344G mutations and three original mutations: tRNAMetT4460C, tRNAMetG4421A, and a 3-bp deletion in the tRNALeu(UUR) gene. Four different large-scale mitochondrial DNA deletions were identified in seven cytochrome c oxidase deficient fibres and in one of the normal ones. There was no evidence of depletion of mitochondrial DNA by in situ hybridisation experiments. Our data show that mitochondrial DNA point mutations, as well as large-scale deletions, are associated with cytochrome c oxidase deficient muscle fibre segments in ageing. Their focal accumulation causes significant impairment of mitochondrial function in individual cells in spite of low overall levels of mitochondrial DNA mutations in muscle.

Aged↗
PubMed2005

Preliminary identification and analysis of point mutations correlated with response to interferon-alpha in hepatitis B virus post-transcriptional regulatory elements.

BACKGROUND: It is still unclear whether viral genetic variability influences response to interferon (IFN)-alpha treatment. Recent reports suggest that IFN-alpha effects may be associated with hepatitis B virus (HBV) post-transcriptional regulation. This study was designed to explore the heterogeneity of HBV post-transcriptional regulatory elements (HPRE) and the relationship between the diversity of HPRE and the response to IFN-alpha treatment. METHODS: The HPRE sequences from 31 Chinese patients infected with HBV were determined by directly sequencing of polymerase chain reaction (PCR) product, and comparing them to those from Caucasian patients. Subsequently, eukaryotic expression vectors containing HPRE at various points were constructed and transfected into HepG2 cells, which were then exposed to recombinant human cytokines. RESULTS: The T to C point mutation at nt 1504 and the C to T (G) at nt 1508 in HPRE were found in 21 and 19 patients with chronic hepatitis B, respectively; the C to T point mutation at nt 1509 was found in 17 patients. These point mutations did not exist in the HPRE of the Caucasian patients. The activity of the CAT gene obviously increased in the case of T to C point mutation at nt 1504, but did not change in the case of the C to T (G) mutations at nt 1508 and 1509. The activity of the CAT gene at these point mutations of HPRE could be inhibited by IFN-alpha/gamma and tumor necrosis factor (TNF)-alpha except for the point mutations at nt 1508 of HPRE which may escape the suppression role of IFN-alpha on HPRE. CONCLUSIONS: There are point mutations between the HPRE of Chinese and Caucasian HBV patients, which might be correlated with response to IFN-alpha. The variation of HPRE might affect the function of HPRE and influence the regulative function of IFN-alpha other than that of IFN-gamma or TNF-alpha on HPRE.

Chloramphenicol O-Acetyltransferase↗
PubMed1997

Frequency of point mutations in the gene for the G-CSF receptor in patients with chronic neutropenia undergoing G-CSF therapy.

Point mutations in the gene for the G-CSF receptor have been reported previously in a subgroup of patients with severe congenital neutropenia. Here, we investigated the frequency of these specific G-CSF receptor mutations in patients with neutropenic disorders undergoing treatment with recombinant human (r-metHu)G-CSF (Filgrastim). Nucleotides 2306 to 2561, including the critical region (nucleotides 2384-2429) from the intracellular domain of the G-CSF receptor gene, were amplified by reverse transcriptase-polymerase chain reaction, and DNA was sequenced directly and after transformation in E. coli. Four of 30 patients with severe congenital neutropenia displayed a point mutation in the tested cytoplasmic region of the G-CSF receptor gene. Two of the four patients with a mutated G-CSF receptor developed acute myeloid leukemia secondary to congenital neutropenia. G-CSF receptor analyses were performed in myeloid cells taken at different time points in the four patients with the mutated receptor, and no correlation between occurrence of the mutation and time or dose of r-metHuG-CSF treatment was found. No point mutations in the G-CSF receptor critical domain could be detected in cells from the other 26 congenital neutropenia patients. Additionally, no G-CSF receptor point mutations could be seen in neutrophils, blood and bone marrow mononuclear cells from patients with cyclic or idiopathic neutropenia, and bone marrow mononuclear cells from patients suffering from severe aplastic anemia. Similar results were obtained by Touw et al., demonstrating that five out of 25 patients with congenital neutropenia reveal G-CSF receptor mutations. These data show that the point mutations in the critical region of the intracellular part of the G-CSF receptor occur only in a subgroup of severe congenital neutropenia patients. Furthermore, our data suggest that the described G-CSF receptor point mutations are not correlated with the start, duration or doses of r-metHuG-CSF treatment, but might result from genetic instability in the G-CSF receptor gene in severe congenital neutropenia.

Adult↗
PubMed2006

The acquisition of full fluoroquinolone resistance in Salmonella Typhi by accumulation of point mutations in the topoisomerase targets.

OBJECTIVES: To determine the contribution to fluoroquinolone resistance of point mutations in the gyrA and parC genes of Salmonella Typhi. METHODS: Point mutations that result in Ser-83-->Phe, Ser-83-->Tyr and Asp-87-->Asn amino acid substitutions in GyrA and Glu-84-->Lys in ParC were introduced into a quinolone-susceptible, attenuated strain of Salmonella Typhi using suicide vector technology. This is the first time that this approach has been used in Salmonella and abrogates the need for selection with quinolone antibacterials in the investigation of resistance mutations. RESULTS: A panel of mutants was created using this methodology and tested for quinolone resistance. The ParC substitution alone made no difference to quinolone susceptibility. Any single GyrA substitution resulted in resistance to nalidixic acid (MIC >or= 512 mg/L) and increased by up to 23-fold the MIC of the fluoroquinolones ofloxacin (MIC Phe or Tyr and Asp-87-->Asn in GyrA with Glu-84-->Lys in ParC) showed high levels of resistance to all the fluoroquinolones tested (MICs: gatifloxacin, 3-4 mg/L; ofloxacin, 32 mg/L; ciprofloxacin, 32-64 mg/L). CONCLUSIONS: In Salmonella Typhi the fluoroquinolones tested act on GyrA and, at higher concentrations, on ParC. The point mutations conferred reduced susceptibility to ofloxacin and ciprofloxacin, and also reduced susceptibility to gatifloxacin. Three mutations conferred resistance to ofloxacin (32 mg/L), ciprofloxacin (32 mg/L) and to the more active fluoroquinolone gatifloxacin (MIC >or= 3 mg/L). These results predict that the use of ofloxacin or ciprofloxacin will select for resistance to gatifloxacin in nature.

Amino Acid Substitution↗
PubMed1995

Analysis of RET protooncogene point mutations distinguishes heritable from nonheritable medullary thyroid carcinomas.

BACKGROUND: The distinction of sporadic from inherited medullary thyroid carcinomas (MTCs) is of clinical importance because of the differences in prognosis, and the need for family screening for genetic counseling required in the latter. Germline mutations in the RET protooncogene are associated with multiple endocrine neoplasia (MEN) type 2A, familial medullary thyroid carcinoma (FMTC), and MEN type 2B. Somatic point mutations in the same gene have been identified in a subset of sporadically occurring medullary thyroid carcinomas. METHODS: A nonisotopic polymerase chain reaction-(PCR) based single strand conformation polymorphism (SSCP) analysis and heteroduplex gel electrophoresis method was used to screen DNA extracted from 32 formaldehyde fixed and paraffin embedded MTC specimens and normal tissue or blood of the same patient for point mutations in RET exons 10, 11, and 16. Point mutations were identified by nonisotopic cycle sequencing of PCR-products using an automated DNA-sequencer. Results were compared with the disease phenotype, clinical findings, and follow-up. RESULTS: Six different missense germline mutations were identified at cysteine residues 618, 630, and 634 of the cysteine-rich extracellular RET domain encoded by exons 10 and 11 in all patients with FMTC and MEN 2A. The frequency of mutations at codon 634 was higher in patients with MEN 2A than with FMTC and a 634 Cys-->Arg mutation was associated with parathyroid disease in three patients. A germline Met-->Thr point mutation at codon 918 of the RET tyrosine kinase domain was identified in all three patients with MEN 2B. Two patients with clinically sporadic MTCs and negative family history exhibited a RET germline mutation at codon 634, indicating the presence of an nonpredicted inherited MTC. Furthermore, one patient had a 618 Cys-->Ser mutation in the tumor and nontumorous thyroid DNA but not in blood DNA, indicating a mosaic mutation affecting thyroid tissue but not blood cells. Tumor specific (somatic) Met-->Thr point mutations at codon 918 were identified in 5 of 13 sporadic MTCs. The remaining eight sporadic MTCs lacked mutations in all three RET exons tested. CONCLUSIONS: This study demonstrates that (1) the molecular methods are not only suitable to identify asymptomatic individuals at risk for MEN 2A, FMTC, and MEN 2B but also to distinguish heritable from nonheritable MTCs using archival tissue specimens, and (2) that more MTCs than clinically expected are heritable, indicating the need for genetic analysis of all patients with MTC.

Adult↗
PubMed1993

K-ras oncogene codon 12 point mutations in testicular cancer.

A significant association between N-ras oncogene activating point mutations and testicular cancer has recently been reported. We have studied DNA samples from the blood and fresh tumor tissues of 17 Norwegian testicular cancer patients (11 seminomas/6 nonseminomas). Point mutations in K-ras-2 and N-ras exons 1 and 2 were studied by denaturing gradient gel electrophoresis (DGGE) and by oligonucleotide hybridization. No N-ras mutations were detected in these tumor samples, but two K-ras-2 exon 1 mutations were found in two of the seminoma tumors (stage I and II tumors) using the DGGE technique. The mutations were confirmed by dot blotting and oligonucleotide hybridization and identified as a G-->T and a G-->A point mutation in K-ras-2 codon 12, leading to a valine and a serine substitution, respectively. All the white blood cell DNAs were negative. As a positive control for DGGE screening, we ran two plasmid constructs carrying human N-ras exon 2 sequences with mutations. To study the role of ras gene activation in testicular cancer, a larger tumor sample population will be investigated.

Adult↗
PubMed2005

Microarray and allele specific PCR detection of point mutations in Mycobacterium tuberculosis genes associated with drug resistance.

Global public health is threatened by the emergence of potentially dangerous antibiotic drug-resistant strains of Mycobacterium tuberculosis. Point mutations in certain M. tuberculosis genes are associated with the resistance of M. tuberculosis strains to antibiotic drugs. The purpose of this study was to develop a suitable microarray-based protocol for the detection of point mutations in M. tuberculosis genes associated with drug resistance. We initially developed a conventional, oligonucleotide microarray protocol and used it to detect and identify on a single microarray slide a number of point mutation-containing rpoB and katG gene target sequences. However, the occurrence of some non-specific hybridization led us to the development of an improved protocol based on allele specific PCR combined with tags/anti-tags and microarrays. This protocol was evaluated by detecting point mutations in M. tuberculosis katG and rpoB gene templates produced by recombinant PCR. The methodology allowed sequences containing single point mutations to be readily distinguished from wild type sequences. The data obtained with the improved protocol had strong and specific signals and relatively low amounts of non-specific hybridization. We successfully used this protocol to detect and identify (<8 h) a number of clinically relevant point mutations in the rpoB, katG and rpsL genes of M. tuberculosis clinical isolates. Our allele specific PCR/tags and anti-tags/microarray protocol has several advantages over our conventional oligonucleotide microarray protocol, and it may have broad applications for point mutation detection.

Alleles↗
PubMed1998

Frequency of the Asn-108 and Thr-108 point mutations in the dihydrofolate reductase gene in Plasmodium falciparum from southwest Colombia.

Several point mutations in the dihydrofolate reductase (DHFR) gene of Plasmodium falciparum have been correlated with in vitro anti-folate drug resistance of laboratory and field isolates. Furthermore, two different point mutations that generate amino acid substitutions at the same position of the enzyme have been observed in all the isolates studied to date. These point mutations change a serine (Ser-108) in the wild type to an asparagine (Asn-108 mutation) or to a threonine (Thr-108 mutation). Using the polymerase chain reaction (PCR), it is possible to identify isolates that present these mutations. We used a mutation-specific PCR to screen 71 samples from several geographic locations of Colombia for the Asn-108 mutation (pyrimethamine resistance). In this initial screening 53 of 71 yielded amplification product with the DHFR mutation-specific primers. We further analyzed the 18 samples that did not amplify using a mutation-specific nested PCR. Of those 18 samples, seven amplified with primers specific for the Thr-108 mutation (proguanil resistance), one with the wild type (Ser-108), and 10 did not amplify. Of these 10 samples, three were identified as P. falciparum using a species-specific diagnostic nested PCR base on sequences from the small ribosomal RNA subunit gene. Overall, 51.6% of the samples amplified for the Asn-108 mutation, 10.9% for the Thr-108 mutation, 35.9% with the wild type specific primer, and 4.8% did not amplify with any of the DHFR primers. We observed variability in the frequency of the mutation between the different geographic location. The frequency of the Asn-108 and Thr-108 mutations in the state of Narifio was 25% each, while in Valle del Cauca the frequencies were 59% and 11%, respectively. These results contrast with observations in Brazil in which the Asn-108 mutation was found in 90% of the blood samples screened.

Adolescent↗
PubMed1991

[Point mutation of c-Ha-ras oncogene in oral cancers].

After sub-sequence of c-Ha-ras oncogene in 11 Chinese oral cancers was amplified with in vitro DNA amplification technique, G----T mutation of c-Ha-ras oncogene at codon 12 was detected by specific mutated oligonucleotide probe, resulting in point mutation of c-Ha-ras oncogene at codon 12 in 4 out of 11 oral cancers which shows that c-Ha-ras oncogene is one of the genes associated with the development and progression of oral cancers, and point mutation may lead to activation of c-Ha-ras oncogene.

Base Sequence↗
PubMed1990

Pancreatic ductal adenocarcinomas induced in Syrian hamsters by N-nitrosobis(2-oxopropyl)amine contain a c-Ki-ras oncogene with a point-mutated codon 12.

We have used the polymerase chain reaction and dideoxynucleotide sequencing to amplify and sequence exons 1 and 2 of the c-Ki-ras proto-oncogene from the normal Syrian golden hamster. Similar methods were employed to screen for the presence of point mutations in the c-Ki-ras oncogene in primary hamster pancreatic ductal adenocarcinomas (PDC) induced by N-nitrosobis(2-oxopropyl)amine (BOP). A GGT to GAT point mutation was detected in codon 12 of the c-Ki-ras gene in 10 primary hamster PDCs. This same point mutation was present in two nonclonal cell lines, PC-1 and PC-1-0, established from tumors that were produced in hamsters by subcutaneously implanting a preparation of minced BOP-induced PDC. Two clonal cell lines, Cl-3 and Cl-7, were cloned from the PC-1 cell line, and these cell lines also carried the GAT point mutation at codon 12. This point mutation was the same as that detected in greater than 75% of adenocarcinomas from the human exocrine pancreas. Thus, our findings provide further validation for the use of the BOP-induced hamster PDC model as a relevant experimental model for human pancreas cancer: not only did the hamster pancreatic ductal adenocarcinomas closely resemble their human counterpart in histopathological morphology and sequential development, but they also contained the same point mutation in codon 12 of the c-Ki-ras oncogene, as has been reported for human pancreatic adenocarcinomas.

Amino Acid Sequence↗
PubMed1992

Ras oncogene point mutations in bladder cancer resistant to cisplatin.

Bladder tumors respond to cisplatin-based chemotherapy in 68% of cases, but only 30% will have a durable response. Recent studies have suggested that ras point mutations may produce cisplatin drug resistance in cell lines. To determine the role of ras point mutations in human tumors resistant to cisplatin, we evaluated ten tumors exposed to cisplatin and eight untreated bladder tumors for ras point mutations. Using polymerase chain reaction DNA amplification and allele-specific oligo-hybridization, we found that only one of the ten treated tumors and none of the untreated tumors harbored a ras point mutation. We conclude that ras point mutations occur infrequently in untreated bladder tumors and do not appear to correlate with cisplatin drug resistance in vivo.

Carcinoma, Transitional Cell↗
PubMed1999

P16 gene deletions and point mutations in patients with agnogenic myeloid metaplasia (AMM).

Studies of p16 alterations with homozygous deletions and mutation analysis were done in 32 patients with agnogenic myeloid metaplasia (AMM) including six patients in leukemic phase. No homozygous deletions were found and, one patient was found to have a shift band in exon 2C fragment by PCR-SSCP analysis. Further sequence analysis demonstrated that the mutated band was a point mutation of G to A in exon 2 codon 140 (GCG-->ACG) causing an amino acid substitution of alanine to threonine demonstrating this patient either carried an mutated gene in one allele as a polymorphism (heterozygous carrier of a mutant p16 gene) or carried a mutant p16 gene clone. This study demonstrates that p16 alterations with homozygous deletions and mutations were very rare in patients with AMM. A single patient found to have a shifted band by PCR-SSCP may be represented as a coincidence or as a polymorphism with a heterozygous carrier of mutated p16 gene, predisposable to AMM or as a mutant p16 gene which can be infrequently observed in this disease.

Blast Crisis↗