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PubMed1992

Thyroxine-binding globulin variant (TBG-Kumamoto): identification of a point mutation and genotype analysis of its family.

Thyroxine-binding globulin (TBG) is the major thyroid hormone transport protein. Several inherited TBG variants resulting in partial or complete TBG deficiencies have been shown to be caused by either one or two nucleotide substitutions, or one nucleotide deletion in the coding regions of the TBG gene. In this report, a Japanese female patient (proband) with hyperthyroid state, whose lower TBG levels did not return to normal under the euthyroid state after treatment was examined. Genomic DNA samples from the proband with thyroxine-binding globulin deficiency (termed TBG-Kumamoto) and her family were subjected to the polymerase chain reaction, and the generated DNA fragments were sequenced. A single nucleotide substitution in the codon for the amino acid 363 of native TBG molecule (CCT to CTT) was found, resulting in the replacement of proline by leucine. It was revealed that the proband was a heterozygote and her father was a hemizygote. The mutation was confirmed by the allele-specific amplification of genomic DNAs from the proband and her father using oligonucleotide primers of normal or mutant residues at the 3' position in the polymerase chain reaction. These results indicate that the abnormality of TBG-Kumamoto is the consequence of this mutation. Genetically, this point mutation observed in TBG-Kumamoto might be classified as a new type of TBG deficiency.

Adult↗

PubMed1996

Constitutive activation of fibroblast growth factor receptor 3 by the transmembrane domain point mutation found in achondroplasia.

Achondroplasia, the most common genetic form of dwarfism, is an autosomal dominant disorder whose underlying mechanism is a defect in the maturation of the cartilage growth plate of long bones. Achondroplasia has recently been shown to result from a Gly to Arg substitution in the transmembrane domain of the fibroblast growth factor receptor 3 (FGFR3), although the molecular consequences of this mutation have not been investigated. By substituting the transmembrane domain of the Neu receptor tyrosine kinase with the transmembrane domains of wild-type and mutant FGFR3, the Arg380 mutation in FGFR3 is shown to activate both the kinase and transforming activities of this chimeric receptor. Residues with side chains capable of participating in hydrogen bond formation, including Glu, Asp, and to a lesser extent, Gln, His and Lys, were able to substitute for the activating Arg380 mutation. The Arg380 point mutation also causes ligand-independent stimulation of the tyrosine kinase activity of FGFR3 itself, and greatly increased constitutive levels of phosphotyrosine on the receptor. These results suggest that the molecular basis of achondroplasia is unregulated signal transduction through FGFR3, which may result in inappropriate cartilage growth plate differentiation and thus abnormal long bone development. Achondroplasia may be one of the number of cogenital disorders where constitutive activation of a member of the FGFR family leads to development abnormalities.

3T3 Cells↗

PubMed1994

[Thyroxine-binding proteins--familial euthyroid hyperthyroxinemia due to point mutations of transthyretin].

Some of the point mutations in transthyretin (TTR) exhibit increased affinity for thyroxine (T4) and result in euthyroid hyperthyroxinemia in affected individuals. TTR, also known as thyroxine binding prealbumin, is a homotetrameric plasma protein of MW 55,000 that transports 15% of serum T4. The known point mutations that cause euthyroid hyperthyroxinemia are Ala109 (ACC) to Thr (GCC) and Gly6 (GGT) to Ser (AGT). These mutations are transmitted by autosomal dominant inheritance. The laboratory findings are an elevated total T4, an increased free T4 index, a normal free T4, and normal levels of total and free triiodothyronine. The Thr109 mutation abolishes Fnu4HI restriction site, and the Ser6 mutation eliminates the Msp I restriction site.

Diagnosis, Differential↗

PubMed1993

c-fms point mutations in acute myeloid leukemia: fact or fiction?

Point mutations in codons 12, 13, and 61 of N-ras have consistently been reported in acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) using a variety of techniques. Recently mutations in codons 301 and 969 of c-fms, preferentially involving TAT-to-TGT at codon 969, have also been identified in these disorders by allele specific oligonucleotide (ASO) hybridization. We have developed allele specific restriction analysis (ASRA) protocols for the detection of point mutations in the critical codons of these genes. ASRA involves enzymatic digestion of polymerase chain reaction (PCR)-induced restriction sites which are specific for normal but not mutant alleles. A total of 11 N-ras mutations were observed in 10 out of 46 AML patients, consistent with the reported frequency of N-ras mutations when alternative techniques of comparable sensitivity are used. In contrast, c-fms point mutations were not detected in a similar number of patients with AML, including 39 studied for mutations in both N-ras and c-fms, and this difference is statistically significant (p < 0.003). A more sensitive technique (ASRA + ASO hybridization) also failed to detect TAT-to-TGT substitutions at codon 969 in a subgroup of M4-AML patients considered to be at greatest risk of harboring c-fms mutations. This study suggests that c-fms mutations at codons 301 and 969 are not important in the pathogenesis of AML in the vast majority of patients.

Acute Disease↗

PubMed2001

Early detection of pancreatic cancer in patients with chronic pancreatitis: diagnostic utility of a K-ras point mutation in the pancreatic juice.

OBJECTIVE: Point mutations of the K-ras oncogene at codon 12 have been described several months before the onset of pancreatic cancer in isolated cases of chronic pancreatitis (CP). The aim of this study was to evaluate the interest of a prospective follow-up of patients with CP and K-ras mutations at codon 12 in the detection of early pancreatic cancer. METHODS: From February 1996 to March 1998, 36 patients (mean age 52.6 yr, 31 men, five women) with CP (alcoholic: 61.1%, pancreas divisum: 5.6%, autoimmune: 5.6%, unknown origin: 27.7%) were included and then prospectively monitored (median duration of 22 months) for detection of pancreatic carcinoma. K-ras point mutations were examined by two-step polymerase chain reaction combined with restriction enzyme digestion in pancreatic juice collected during endoscopic retrograde pancreatography. RESULTS: Ten patients (27.8%) were positive for K-ras mutation. Patients with and without the mutation were not different with respect to age and sex ratio. K-ras mutations were homogeneously distributed according to the etiology (alcoholic vs nonalcoholic) and morphological characteristics (ductal stricture or mass vs none) of CP. A pancreatic carcinoma was discovered at an invasive stage in two patients, respectively at 7 and 17 months after disclosure of a K-ras mutation, versus none in patients without the mutation (p < 0.02). CONCLUSIONS: Presence of a K-ras gene mutation is not rare in patients with CP and represents an increased risk of developing pancreatic cancer. However, its utility for the detection of early pancreatic cancer remains doubtful in clinical practice.

Adenocarcinoma↗

PubMed1994

Type and number of Ki-ras point mutations relate to stage of human colorectal cancer.

Point mutations in the Ki-ras gene belong to the genetic key events in tumorigenesis of colorectal cancer. The type and number of point mutations were detected in specimens from patients with colorectal carcinomas stages as Dukes B and C using single-stranded conformational polymorphism analysis and sequencing. G-A transitions in codon 12 were exclusively found in Dukes B tumors, G-T transversions mainly in Dukes C, and G-C transversions only in Dukes C tumors. Apparently, the G-T and G-C transversions are associated with metastatic behavior of colorectal carcinomas, while G-A transitions are not. In several samples, multiple point mutations could be detected in codon 12, the frequency of multiple mutations increasing with the stage of the tumor.

Base Sequence↗

PubMed1994

[Point mutation at codon 12 of c-Ki-ras oncogene in human pancreatic neoplasms and normal human pancreas tissue].

Point mutation at codon 12 of c-Ki-ras oncogene was tested from 2 normal human pancreas, 7 pancreatic endocrine neoplasms and 15 pancreatic adenocarcinomas, including 5 resected pancreatic adenocarcinomas, 3 cell lines of pancreatic adenocarcinoma and 7 nude mice transplanted tumors by dot blot and single-strand conformation polymorphism (SSCP) after PCR amplification, c-Ki-ras codon 12 point mutation was found only in pancreatic adenocarcinomas (11/15 by dot blot and 13/15 by SSCP). No mutation was detected in normal human pancreatic tissue and endocrine tumors. By our experience, SSCP is more convenient and faster than dot blot in detecting gene mutation. Point mutation at codon 12 of c-Ki-ras oncogene may play an important role in the development of human pancreatic carcinoma.

Adenocarcinoma↗

PubMed1997

Development of a point mutation assay for the detection of human cytomegalovirus UL97 mutations associated with ganciclovir resistance.

A point mutation assay was developed to detect the quantitative prevalence of mutations at codons 460 (M to I; M to V), 520 (H to Q), 594 (A to V) and 595 (L to F; L to S) within the UL97 gene of human cytomegalovirus which segregate with ganciclovir resistance. Synthetic mixtures of wild-type and mutant plasmids containing the UL97 gene were amplified by nested polymerase chain reaction and the 700 base pair amplicon subsequently subjected to the point mutation assay. In plasmid reconstruction experiments, there was a high correlation between experimentally derived percentage mutant with the theoretical values. The assay was then used to assess the changes in the genetic composition of the UL97 gene in three patients on prolonged ganciclovir therapy. All three patients developed genotypic resistance against ganciclovir involving mutation at codon L595S, L595F and double mutation at codons L595F and M460I. In one patient, alteration of therapy to foscarnet did not affect the composition of UL97 and virus remained genotypically resistant to ganciclovir. In contrast, in two patients whose therapy was altered to cidofovir (HPMPC), repopulation with cytomegalovirus strains carrying the wild-type (ganciclovir-sensitive) codon at positions 595 and 460 occurred. The potential use of this assay for the rapid detection of cytomegalovirus resistance in patients on long-term ganciclovir therapy is discussed.

Acquired Immunodeficiency Syndrome↗

PubMed1977

Validation of the in vivo somatic mutation method in the mouse as a prescreen for germinal point mutations.

The in-vivo somatic mutation method developed by us in an earlier X-ray experiment was tested for its usefulness in chemical mutagenesis work, specifically in the prescreening for germinal point mutations. In order to explore possible parallelisms, the 7 compounds chosen for study, as well as the genetic markers used, were those with which large-scale specific-locus mutation-rate experiments in germcells had been conducted in the past or were in progress. From 1--3 dose levels were tested for each compound. On day 10 1/4 after copulation of C57BL females with T males, a single injection of the test compound was administered, and about 2000 offspring altogether were subsequently scored for survival, morphology, and presence of spots of various types. In accordance with our earlier results we found 3 types of spots: white near midline ventral spots (WMVS) which probably result from killing of melanocyte precursor cells; spots resulting from misdifferentiation; and the remainder, which probably result from expression of the recessive by one of several mechanisms (RS). Induction of teratogenic effects, which were stage-specific rather than agent-specific, generally paralleled induction of WMVS's. Both are interpreted as resulting from cell killing. Induction of RS's did not always parallel induction of WMVS's, but roughly paralleled relative frequencies of specific-locus mutations induced in spermatogonia by the same compounds. Even though the in vivo somatic-mutation method probably detects genetic changes additional to point mutations, the results indicate that it may be a useful prescreen for germinal specific-locus mutations, provided care is taken to distinguish between the 3 types of spots, only one of which (RS) is indicative of expression of the recessive.

Animals↗

PubMed2001

Melting temperature analysis as quantitative method for detection of point mutations.

Different methods have been devised to detect point mutations. Some are very sensitive, detecting mutations even in a background of normal tissue, but none provide information about the percentage of cells with mutant DNA. Here we describe an easy, fast and reliable method, melting temperature analysis, which not only detects point mutations but also provides quantitative information on the percentage of cells with mutant DNA. By this method we detected a G-A transition in codon 12 of the K-ras gene in DNA of subjects with colorectal cancer. The K-ras mutation was found in 9/10 bowel cancers and 8/10 normal adjacent samples. It was also detected in 4/7 stool samples from the same patients. In colorectal cancers, the proportion of K-ras mutant cells was variable: in two the mutant/wild-type DNA ratio was 30/70, in three 50/50, and in four 70/30. Melting temperature analysis was sensitive for the detection of point mutations in bowel cancer and also in apparently normal tissue, providing quantitative information about the percentage of cells with mutant DNA.

Colorectal Neoplasms↗

PubMed1994

K-ras gene point mutation: a stable tumor marker in non-small cell lung carcinoma.

K-ras gene point mutation is a highly frequent event in human malignancy. About one third of non-small cell lung cancer (NSCLC) patients harbor K-ras gene point mutational activations. This study investigates the prevalence of K-ras mutation in autopsy tumors with NSCLC, and the correlation of K-ras gene point mutations between primary tumors and metastases in NSCLC. Formalin-fixed, paraffin-embedded tissue sections of 15 primary lung tumors and their metastases, (obtained from autopsy), were examined for the presence of point mutations in K-ras gene codon 12, 13 and 61 by oligodeoxynucleotide hybridization analysis of DNA fragments, amplified by polymerase chain reaction (PCR). K-ras gene point mutations were detected in five cases of lung carcinoma, of which four were adenocarcinomas and one was squamous cell carcinoma. In each of these cases, identical K-ras gene mutations were found in the DNA of both the primary tumor and its corresponding distant metastases. Activating K-ras base-substitutions correlate well between the primary tumor and its corresponding metastases in NSCLC. In the negative cases where no K-ras mutation was found in the primary tumors, no newly acquired K-ras mutation appeared in the metastases. Our study indicates that K-ras point mutation serves as a stable tumor marker in NSCLC.

Adenocarcinoma↗

PubMed1998

Cytochrome c oxidase deficiency associated with the first stop-codon point mutation in human mtDNA.

We have identified the first stop-codon point mutation in mtDNA to be reported in association with human disease. A 36-year-old woman experienced episodes of encephalopathy accompanied by lactic acidemia and had exercise intolerance and proximal myopathy. Histochemical analysis showed that 90% of muscle fibers exhibited decreased or absent cytochrome c oxidase (COX) activity. Biochemical studies confirmed a severe isolated reduction in COX activity. Muscle immunocytochemistry revealed a pattern suggestive of a primary mtDNA defect in the COX-deficient fibers and was consistent with either reduced stability or impaired assembly of the holoenzyme. Sequence analysis of mtDNA identified a novel heteroplasmic G-->A point mutation at position 9952 in the patient's skeletal muscle, which was not detected in her leukocyte mtDNA or in that of 120 healthy controls or 60 additional patients with mitochondrial disease. This point mutation is located in the 3' end of the gene for subunit III of COX and is predicted to result in the loss of the last 13 amino acids of the highly conserved C-terminal region of this subunit. It was not detected in mtDNA extracted from leukocytes, skeletal muscle, or myoblasts of the patient's mother or her two sons, indicating that this mutation is not maternally transmitted. Single-fiber PCR studies provided direct evidence for an association between this point mutation and COX deficiency and indicated that the proportion of mutant mtDNA required to induce COX deficiency is lower than that reported for tRNA-gene point mutations. The findings reported here represent only the second case of isolated COX deficiency to be defined at the molecular genetic level and reveal a new mutational mechanism in mitochondrial disease.

Adult↗

PubMed2001

Point mutations of muscle mitochondrial DNA from patients with mitochondrial encephalomyopathies.

OBJECTIVE: To study the relation between point mutations at nt3243 and nt8344 of muscle mitochondrial DNA from patients with mitochondrial encephalomyopathies and phenotypes. METHODS: DNA was extracted from muscle specimens from 5 patients with mitochondrial encephalomyopathies and and amplified by PCR method, using corresponding oligonucleotide primers. DNA fragments were digested with restriction enzymes Bgl I and Apa I, then the digested DNA fragments were analyzed with an electrophoresis method. RESULTS: The point mutation at nt3243 of mtDNA was found in 2 patients, one with mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS) and another with myoclonic epilepsy with ragged red fibers (MERRF). The point mutation at nt8344 was found in 2 patients with MERRF, including the one with point mutation at nt3243. CONCLUSION: The point mutation of DNA at nt3243 correlated with MELAS and nt8344 correlated with MERRF. In addition, the detection of point mutations at both nt3243 and nt8344 in a patient with MERRF shows the association of mutation with diversity in clinical manifestations of mitochondrial encephalomyopathies.

Adolescent↗

PubMed2002

Frameshift mutations of RIZ, but no point mutations in RIZ1 exons in malignant melanomas with deletions in 1p36.

Recently, the retinoblastoma protein interacting zinc finger gene RIZ has been proposed as a candidate for the tumor suppressor locus on 1p36, because of the common loss of RIZ1 RNA in human tumors. In addition, frameshift mutations of this gene have been demonstrated in a variety of tumors with microsatellite instability. Since alterations in this region have been described in malignant melanomas, we investigated DNA of paraffin-embedded sections from 16 typical naevi, 19 atypical naevi, 33 primary melanoma lesions and 25 metastases and DNA from four melanoma cell lines by PCR and direct sequencing analysis of RIZ. Frameshift mutations in the RIZ gene were found in 17% of melanoma samples and 8.6% of naevi, but we could not demonstrate any missense mutations in the exons of RIZ1. No LOH of the RIZ gene nor any microsatellite instability in six dinucleotide markers or in the mononucleotide repeats IGRIIR, hMSH3, and hMSH6 could be demonstrated in the samples with RIZ frameshift mutations. Although our results do not explain the high rate of deletions in 1p36 found in this tumor, they assign RIZ a potential role in the multi-step tumor forming process of malignant melanoma of the skin.

Cell Transformation, Neoplastic↗

PubMed2002

Detection of A3243G point mutation in mitochondrial DNA from 10 cases of MELAS.

OBJECTIVE: To search for A3243G point mutations in mitochondrial DNA (mtDNA) from 10 cases of mitochondrial encephalomyopathy, lactic acidosis and strokelike episodes (MELAS). METHODS: Using PCR-restriction analysis, we investigated A3243G point mutations in mtDNA of muscle and/or blood cells from 10 patients and their 8 maternal relatives. We also quantitated the A3243G mtDNA in samples harboring the mutation. RESULTS: A3243G point mutations were identified in all muscle and/or blood samples from 10 MELAS patients. The proportion of mutant mtDNA was 10.8%-47.8% in blood (7 cases), and 39.4%-67.7% in muscle (5 cases). This ratio was invariably higher in muscle than in blood from two patients whose blood and muscle samples were both available. Younger patients usually carried higher proportions of A3243G mutant mtDNA in blood. Eight maternal relatives from 6 families were also examined. Maternal transmission of the disease could be identified in one family. No A3243G point mutations were found in mothers' blood from 3 families and siblings' blood from 2 families. CONCLUSIONS: All 10 MELAS patients were found to have the mtDNA A3243G mutation in their muscle and/or blood. The A3243G mutation seems to be sporadic in 5 of the families examined, suggesting the mechanism of de novo mutation for the pathogenesis of their MELAS syndrome.

Adolescent↗

PubMed1995

Screening for mitochondrial DNA (mtDNA) point mutations using nonradioactive single strand conformation polymorphism (SSCP) analysis.

OBJECTIVES: Mitochondrial cytopathies such as Leber's hereditary optic neuropathy (LHON), mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS), and myoclonus epilepsy with red ragged fibers (MERRF) are associated with distinct mtDNA point mutations (for review see 1). LHON, for example, is related to at least 14 mtDNA point mutations within different mitochondrially encoded respiratory subunit genes. In addition, the number of newly found LHON-related mutations is increasing. In the light of the large number and the dispersed distribution of these point mutations throughout the mitochondrial genome, screening for these by sequencing all of suspected loci is laborious and time-consuming. In order to facilitate a rapid screening for mitochondrial point mutations we have evaluated the use of polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) for the analysis of the human mitochondrial genome. DESIGN AND METHODS: In a first evaluation step we created a variety of pUC18 clones derived from mitochondrial control region amplifications with defined sequence differences and length. These clones were used as standard material for an optimization of the PCR-SSCP analysis. The optimized PCR-SSCP was then applied to large cohorts of patients with known, i.e., sequenced mtDNA point mutations and to healthy controls in order to evaluate its sensitivity. RESULTS: The most common LHON-related mtDNA point mutations at nucleotide positions (nps) 11778, 14484, 4216, could be detected by SSCP analysis, as well as the heteroplasmic np 3243 MELAS associated point mutation. Several new polymorphisms and point mutations were found. A sensitivity, i.e., the ability to detect defined point mutations, of 93% (clones) and 98% (disease controls) was achieved when comparing SSCP- and direct sequencing results. CONCLUSION: The PCR-SSCP approach using a non-radioactive silver staining method is suited for the detection of human mitochondrial point mutations, as well as a helpful screening tool for novel mt DNA mutations.

Base Sequence↗

PubMed1994

Functional and morphological abnormalities of mitochondria in human cells containing mitochondrial DNA with pathogenic point mutations in tRNA genes.

mtDNA with a point mutation in the tRNA(Ile) gene at nucleotide position 4269 found in a patient with fatal cardiomyopathy and mtDNA with a point mutation in the tRNA(Arg) gene at 10410 found in a patient with Alpers disease were transferred cytoplasmically to rho zero HeLa cells (HeLa cells lacking mtDNA) to determine whether these novel mtDNA mutations in the tRNA genes are responsible for the defects in mitochondrial respiration function observed in these diseases. Cybrid clones (clones of rho zero HeLa cells with mtDNA from the patients) were isolated, and respiratory function and morphology of the mitochondria of the cybrid clones containing wild-type mtDNA and mutant mtDNA predominantly were compared. The results showed that accumulation of mutant mtDNA at 4269 alone without defects in the nuclear genome was sufficient to produce a disease phenotype, while mutant mtDNA at 10410 was not related to pathogenesis and reflected one of the rare polymorphic sites of human mtDNA. Moreover, we found that mitochondria in living cells were significantly swollen only when they contained predominantly the pathogenic mutant mtDNA, suggesting that the functional abnormality of mitochondria induced by pathogenic mtDNA mutations in tRNA genes is always associated with their swollen structure.

Cardiomyopathies↗

PubMed1998

Correlation of N-ras point mutations with specific chromosomal abnormalities in primary myelodysplastic syndrome.

A cytogenetic and N-ras point mutation study was done in patients with primary myelodysplastic syndrome (MDS) from Rio de Janeiro, Brazil, in order to evaluate the progression of preleukemic states to overt leukemia. Cytogenetic analysis was performed in 50 patients with MDS and clonal chromosomal abnormalities were detected in 19 (38%) of them. Patients with refractory anemia (RA) or with ringed sideroblasts (RARS) presented normal karyotypes or single abnormalities as del(5q) or -Y, while patients in more advanced states as RA with excess of blasts (RAEB), RAEB in transformation (RAEB-t) and chronic myelomonocytic leukemia (CMML) showed complex karyotypes and single abnormalities involving chromosomes 7 or 8, which were related to poor prognosis and elevated risk of transformation to acute myeloid leukemia (AML). The frequency of ras activation was studied in these 50 patients with MDS. Samples of bone marrow were screened for oncogenic point mutations by DNA amplification followed by oligonucleotide hybridization analysis (PCR-ASO) at codon 12 of N-ras proto-oncogene. We detected N-ras point mutations in 21 patients (42%). Progression from MDS to AML was observed in 9 patients (18%). The correlation analysis between N-ras point mutations and specific chromosomal abnormalities indicated that although mutated N-ras was found in cells with del(5q) and monosomy 7, cells with those abnormalities and normal N-ras were also identified. Otherwise trisomy of chromosome 8 showed a correlation with N-ras point mutations and in all cases, patients showed progression of MDS to AML during the follow-up study. MDS comprises a heterogeneous group of hematopoietic disorders and probably several steps are implicated in the evolution to AML. In this work we suggest that one possible pathway of leukemogenesis in MDS includes N-ras point mutations in association with trisomy of chromosome 8.

Adolescent↗