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At least 127 records · Page 7Linked to original sources
PubMed1998

Congenital adrenal hypoplasia: clinical spectrum, experience with hormonal diagnosis, and report on new point mutations of the DAX-1 gene.

X-linked congenital adrenal hypoplasia (AHC) is a rare developmental disorder of the human adrenal cortex and is caused by deletion or mutation of the DAX-1 gene, a recently discovered member of the nuclear hormone receptor superfamily. Hypogonadotropic hypogonadism is frequently associated with AHC. AHC occurs as part of a contiguous gene syndrome together with glycerol kinase deficiency (GKD) and Duchenne's muscular dystrophy. The present series, collected over the past 2 decades, includes 18 AHC boys from 16 families: 4 with AHC, GKD, and Duchenne's muscular dystrophy; 2 with AHC and GKD; and 12 with AHC (5 young adults with hypogonadotropic hypogonadism). Most of the boys presented with salt wasting and hyperpigmentation during the neonatal period. Plasma steroid determinations performed in the first weeks of life often showed confusing results, probably caused by steroids produced in the neonates' persisting fetocortex. Aldosterone deficiency usually preceded cortisol deficiency, which explains why the patients more often presented with salt-wasting rather than with hypoglycemic symptoms. An ACTH test was often necessary to detect cortisol deficiency in the very young infants. In some patients, serial testing was necessary to establish the correct diagnosis. In 4 boys studied during the first 3 months after birth, we found pubertal LH, FSH, and testosterone plasma levels indicating postnatal transient activation of the hypothalamic-pituitary-gonadal axis as in normal boys. Previous studies have shown that the DAX-1 gene is deleted in the AHC patients with a contiguous gene syndrome and is mutated in nondeletion patients. Most of the point mutations identified in AHC patients were frameshift mutations and stop mutations. In the 15 patients available for molecular analysis of the DAX-1 gene, there were large deletions in 6 patients and point mutations in another 7 patients. All of the point mutations identified in the present study resulted in a nonfunctional truncated DAX-1 protein. Two brothers with primary adrenal insufficiency and a medical history that strongly suggested AHC had no mutation in the DAX-1 gene. Thus, additional, as yet unknown genes must play a part in normal adrenal cortical development.

Adrenal Insufficiency↗
PubMed1987

Point mutations as an optimal search process in biological evolution.

Point mutations are pictured as jumps in a phase space representing the sequences of amino acids or nucleotides as discrete points. It is shown that this space can be given a natural metric by quantifying common physical and chemical properties of amino acid constituents in terms of a natural measure. Evolution through point mutations is simulated by the search for points in the phase space representing amino acid sequences of high survival fitness. Due to the local compactness of the distribution of these functionally allowed points in phase space any successful search procedure has characteristics qualitatively different from those in the case of a random distribution. This is demonstrated by model calculations. A specified distribution of allowed points is generated with subsequent evaluation of the success of the retrieval process as a function of the jump probabilities between lattice sites. The results of such simulations are compared with data obtained from the analysis of the DNA or mRNA sequences coding related proteins. By counting silent and expressed nucleotide replacement frequencies one can draw conclusions as to the efficacy of the natural evolutionary search processes in the phase space of amino acid sequences. There are cases, where the highest possible information gain of one bit per accepted point mutation is achieved. In general the information gain is found to be somewhat sub-maximal due to functional requirements.

Amino Acid Sequence↗
PubMed2002

[Analysis on point mutation of the CDKN2/p16 gene in lung cancer].

OBJECTIVE: To study the status of CDKN2/p16 gene point mutation in lung cancer. METHODS: Polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) and sequencing were used to detect the point mutation of CDKN2/p16 gene exon 2 in 89 cases of lung cancer. RESULTS: In 69 cases of the lung cancer without deletion of CDKN2/p16 gene exon 2, 16 cases were found to have suspicious abnormality of CDKN2/p16 gene exon 2 by PCR-SSCP, and in these 16 cases, 9 were found to harbor point mutations of CDKN2/p16 gene exon 2 by automated sequencing analysis. CONCLUSION: The point mutation is one of the mechanisms for CDKN2/p16 gene inactivation, but it is not the chief mechanism. The inactivation of CDKN2/p16 gene aroused by point mutation plays a role to some extent in the genesis and progression of lung cancer.

Cyclin-Dependent Kinase Inhibitor p16↗
PubMed1995

SHC and GRB-2 are constitutively by an epidermal growth factor receptor with a point mutation in the transmembrane domain.

A single point mutation, Glu627--> Val, equivalent to the activating mutation in the Neu oncogene, was inserted in the transmembrane domain of the human epidermal growth factor (EGF) receptor. Unlike the wild type, Glu627-EGF receptor, transfected in NIH3T3 cells, gave rise to focal transformation and growth in agar even in the absence EGF. Constitutive activity of mutant EGF receptor amounted to 20% of that of wild type receptor stimulated by EGF. In addition, the mutant receptor was more sensitive to EGF, reaching maximum transforming activity at 5 ng/ml EGF. NIH3T3 cells expressing Glu627-EGF receptor showed a transformed phenotype and were not arrested in G0 upon serum deprivation. The mutant receptor was constitutively autophosphorylated, and several other cellular proteins were phosphorylated on tyrosine in absence of the ligand. Among these, the SHC adaptor protein was phosphorylated in absence of EGF, the other adaptor, GRB-2 was constitutively associated with the Glu627-EGF receptor in vivo and in vitro, and mitogen-activated protein kinase was constitutively phosphorylated. In contrast, other EGF receptor substrates, like phospholipase C gamma, were not phosphorylated in absence of EGF. The mutant receptor showed a higher sensitivity to cleavage by calpain both in absence and presence of EGF, appeared as a 170- and 150-kDa doublet in cell extracts, and a specific calpain inhibitor blocked the appearance of the 150-kDa form. Since the calpain cleavage site is located in the receptor cytoplasmic tail, this finding suggests that the Glu627 mutation induces a slightly different conformation in the EGF receptor intracellular domain. In conclusion, our data show that a point mutation in the EGF receptor transmembrane domain was able to constitutively activate the receptor and to induce transformation via constitutive activation of the Ras pathway.

3T3 Cells↗
PubMed1997

Detection of p53 point mutations in primary human vulvar cancer by PCR and temperature gradient gel electrophoresis.

Clinical and experimental evidence is consistent with a key role of point mutations of the p53 tumor suppressor gene in the etiology of squamous cell carcinoma. To determine the relation of tumor behavior and patient survival in vulvar cancer in regard to p53 status, we retrospectively analyzed 38 paraffin-embedded specimens of primary vulvar cancer for genetic alterations of exons 5-8 of the p53 gene. For detection of p53 point mutations we used in vitro amplification by polymerase chain reaction (PCR) and temperature gradient gel electrophoresis (TGGE) and, as a detection method, direct sequencing for mutation verification. p53 point mutations were detected in 12/38 tumor specimens. Patients bearing p53 point mutations showed a significantly shorter relapse-free (log-rank test, P = 0.002) and overall survival time (log-rank test, P = 0.0006). We conclude that PCR-TGGE is an appropriate method for detection of p53 point mutations in paraffin-embedded material. We show that loss of wild-type p53 is an adverse prognostic factor in patients suffering from vulvar cancer.

Adult↗
PubMed2000

Frataxin point mutations in two patients with Friedreich's ataxia and unusual clinical features.

Two patients with a progressive ataxia are presented with clinical features consistent with classic Friedreich's ataxia (FRDA), but also with features unusual for FRDA. Analysis of DNA showed that each patient is heterozygous for the expanded GAA repeat of FRDA, but carries a base change on his other frataxin allele. For one patient a non-conservative arginine to cysteine amino acid change is predicted at amino acid 165 whereas the other mutation is found at the junction of exon one and intron one. Muscle biopsy showed an absence of frataxin immunoreactivity in the patient harbouring the intronic mutation, confirming the pathological nature of the base change. These mutations extend the range of point mutations seen in FRDA, and agree with recent reports suggesting phenotypic variation in patients with FRDA harbouring point mutations in conjunction with an expanded GAA repeat.

Child↗
PubMed1995

Efficient induction of point mutations allowing recovery of specific locus mutations in zebrafish.

A technique is described that greatly increases the efficiency of recovering specific locus point mutations in zebrafish (Danio rerio). Founder individuals that were mosaic for point mutations were produced by mutagenizing postmeiotic gametes with the alkylating agent N-ethyl-N-nitrosourea. Under optimal conditions, each founder carried an average of 10 mutations affecting genes required for embryogenesis. Moreover, approximately 2% of these founders transmitted new mutations at any prespecified pigmentation locus. Analyses of new pigmentation mutations confirmed that most were likely to be point mutations. Thus, mutagenesis of postmeiotic gametes with N-ethyl-N-nitrosourea yielded frequencies of point mutations at specific loci that were 10- to 15-fold higher than previously achieved in zebrafish. Our procedure should, therefore, greatly facilitate recovery of multiple mutant alleles at any locus of interest.

Animals↗
PubMed1992

[MELAS associated with diabetes mellitus and point mutation in mitochondrial DNA].

Point mutation of mitochondrial DNA has been described in the blood from a MELAS patient. The 39-year-old patient developed progressive dementia, stroke-like episodes, heart conduction defect (Lown-Ganong-Levin syndrome) and cortical blindness. CT scan revealed brain atrophy and low density areas in the bilateral occipital lobes. Laboratory tests showed hyperglycemia and lactic acidosis. Muscle biopsy showed ragged red fibers on Gomori trichrome staining. He was clinically diagnosed as having MELAS and insulin-dependent diabetes mellitus. Onset of diabetes mellitus and MELAS was almost same. Family history showed his mother's brother and sisters had also insulin-dependent diabetes mellitus. We amplified the leucine (UUR) tRNA gene from the patient's blood with polymerase chain reaction (PCR) and analysed it by restriction enzyme analysis and sequencing. Genetic analysis showed A-to-G substitution at the nucleotide position 3243 in the leucine (UUR) tRNA gene. This substitution made a new restriction site Apa I. Mutant DNA coexisted with wild type DNA (heteroplasmy). It is shown that in some types of mitochondrial encephalomyopathies, especially patients of Kearns-Sayre syndrome (KSS), diabetes mellitus is often complicated. And in KSS patients insulin receptor in normal, but insulin secretion from beta cells of pancreas is decreased. In MELAS patients, however, has diabetes mellitus been reported to be rarely complicated and relationship between MELAS and diabetes mellitus is not done. As far as we know, two cases, including ours, with genetically diagnosed MELAS have been reported to have diabetes mellitus.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2001

[The study of point mutation of muscular mitochondrial DNA from patients with mitochondrial encephalomyopathies].

OBJECTIVE: To study the relation between the point mutation at nt3243 and nt8344 of muscular mitochondrial DNA from patient with mitochondrial encephalomyopathies and phenotypes. METHODS: The total DNA was extracted from muscle specimens from 5 patients with mitochondrial encephalomypathies and amplified by PCR method using corresponding oligonucleotide primers. The DNA fragments were digested with the restriction enzyme Bgl I and Apa I, then the digested DNA fragments were analyzed with electrophoresed method. RESULTS: The point mutation at nt3243 of mtDNA was found in 2 patients, 1 with MELAS and another with MERRF. The point mutation at nt8344 was found in 2 patients with MERRF, including the one with point mutation at nt3243. CONCLUSIONS: There was a correlation of the point mutation of DNA at nt3243 with MELAS,and at nt8344 with MERRF. In addition, The detection of point matation at both nt3243 and nt8344 in patient with MERRF shows the association of matation with diversity in clinical manifestion of mitichondrial encephalomypathies.

Adolescent↗
PubMed1977

The protein-mapping-method employed to test for chemically induced point mutations in mice.

A test system for detecting point mutations chemically induced in the germ cells of mice has been proposed in the past. In the present investigation the effect of the mutagenic substance methylnitrosourea (MNU) in such a test system was studied. Male mice 10-12 weeks of age of the inbred strain BALB/c Han. were treated with MNU. Doses ranging from 40-150 mg/kg were administered over different time periods ranging from 4-14 days. Treatments were scheduled so that spermatogonia in resting or mitotic stages at the time of exposure to MNU would be mature sperm at the time of mating of the males. Proteins of the liver from F1-foetuses were separated by isoelectric focusing followed by electrophoresis (protein-mapping-method). The protein patterns were analysed for new protein spots which should suggest point mutations. The results obtained showed no protein variations in the patterns of 312 control animals (foetuses). However, two individuals with a variant protein were found among a relatively small group of 72 out of 463 treated animals. The animals of this group are offspring of male parents in which the spermatogonia were treated at the mitotic phase with the highest total dose (except the lethal dose) employed in this study. The results suggest that MNU, under these conditions, is capable of inducing point mutations in the germ cells of mice. Furthermore, the mutagenicity test system imployed by this investigation for the first time seems to be a useful system possessing relatively high sensitivity.

Animals↗
PubMed1996

Temperature-programmed capillary electrophoresis for detection of DNA point mutations.

A method for unambiguous determination of point mutations in genomic DNA, based on electrophoresis in thin capillaries, is reported here. The method is based on the principle of temperature gradient gel electrophoresis (TGGE), a variant of denaturing gradient gel electrophoresis (DGGE), and exploits the differential melting of mutant and wild-type PCR-amplified DNA fragments during electrophoresis through a temperature gradient. Unlike TGGE, where the temperature gradient exists along the separation space, the denaturing temperature gradient in the fused-silica capillaries is time-programmed, so as to reach the melting points (Tms) of all species under analysis prior to electrophoretic transport past the detector window. The DNA fragments are injected in a capillary maintained (by combined chemical and thermal means) just below the expected Tm values. The temperature increment applied is typically minute (1 degree -1.5 degrees C) and the sweep speed is rather shallow (e.g., 0.05 degree C/min). Additionally, the denaturing thermal gradient is not controlled externally, but generated internally by Joule heat produced by voltage ramps. Point mutants are fully resolved into a spectrum of four bands, with a dynamic range extending from 45 degrees C (low melters) up to 70 degrees C for high melters. The present method can thus be universally applied to any type of point mutation.

DNA↗
PubMed1998

Novel point mutations and allele loss at the RET locus in sporadic medullary thyroid carcinomas.

Germline mutations in the RET proto-oncogene have been shown to be the underlying cause of multiple endocrine neoplasia type 2 (MEN 2A and 2B) and familial medullary thyroid carcinoma (FMTC). Some cases of sporadic medullary thyroid carcinoma (sporadic MTC) are reported to have specific codon 918, 883 and 768 mutations of the RET gene in tumor tissues. We examined RET gene mutations in 40 Japanese cases who had previously undergone surgery for sporadic MTC. DNA extracted from formalin-fixed tumor tissues and corresponding normal thyroid tissues or peripheral blood leukocytes was analyzed for mutations of exon 10, 11, 13, 14 and 16 of the RET gene by DNA sequencing and by mutation-specific restriction enzyme analysis. Germline RET point mutations were found in six of 40 cases (15%), cysteine residues at codon 618 in two, codon 634 in three and valine residue at codon 804 in one, and were newly identified as heritable MTC. Of the remaining 34 sporadic MTC cases, four (12%) had tumor-specific RET point mutations. Two were found in exon 16; one case showed an ATG to ACG (Met to Thr) mutation at codon 918, and the other showed two point mutations, ATG to ACG (Met to Thr) at codon 918 and GCA to GTA (Ala to Val) at codon 919 with loss of the wild-type allele, suggesting that both alleles at the RET locus were altered. The other two were found in exon 13; one case showed a CCG to TCG (Pro to Ser) mutation at codon 766 and the other showed a silent mutation, GTC to GTT (Val) at codon 778 with loss of the wild-type allele. There was no association of sporadic mutations with recurrence or prognosis in patients with sporadic MTC. The low rate of somatic RET mutation at codon 918 in our sporadic MTC suggests that as yet unknown factors may be involved. Genetic alterations in both alleles may have an important role in small fraction of sporadic MTCs.

Adult↗
PubMed1996

K-ras point mutations are rare events in premalignant forms of Barrett's oesophagus.

OBJECTIVE: In Barrett's adenocarcinomas, in contrast to squamous oesophageal carcinomas, K-ras point mutations are thought to be a frequent event. The frequency of K-ras point mutations in premalignant forms of Barrett's oesophagus (metaplasia, dysplasia) leading to adenocarcinoma with increased risk is currently not known. To establish the frequency of K-ras mutations in premalignant forms of Barrett's oesophagus, we investigated oesophageal biopsy specimens with Barrett's metaplastic and dysplastic epithelium for point mutations in the K-ras gene/codons 12, 13. DESIGN: A total of 412 biopsies from patients with Barrett's oesophagus were histologically classified into biopsies with metaplasia (n = 252), dysplasia (n = 105) and adenocarcinoma (n = 11), as well as biopsies distant from disease (normal, n = 37 and hyperplastic squamous epithelium, n = 7). METHODS: DNA from biopsy specimens was amplified by polymerase chain reaction (PCR) with a modified primer for generating a restriction site in the case of wild type in codon 12. Wild-type or point mutations in the K-ras gene/codons 12, 13 were detected by restriction fragment length analysis of the PCR products. RESULTS: Point mutations in K-ras/codon 12 were found in 9 biopsies (n = 1 in metaplasia, n = 4 in dysplasias, n = 4 in adenocarcinomas). All the other biopsies showed the wild type of K-ras/codon 12. No K-ras/codon 13 mutation (GGCgly-->GACasp) was observed. CONCLUSION: Mutations in K-ras/codon 12 were rarely found in premalignant forms of Barrett's oesophagus. Whereas the screening for K-ras point mutations in metaplastic sites of Barrett's epithelium seems not to be of practical value, the screening for mutations in dysplastic lesions might be helpful to estimate the individual risk for progression of Barrett's epithelium to adenocarcinoma. A further evaluation in larger numbers of patients is needed.

Adenocarcinoma↗
PubMed1997

Identification and comparison of point mutations associated in classic and variant infectious bursal disease viruses.

Restriction enzymes (RE) were used to identify point mutations in the nucleotide sequences of the infectious bursal disease virus (IBDV) strains Del-E, Del-A, STC, IN, Bursine 2, and Bio-Burs. The point mutations at amino acid sites 222, 254 and 323 were identified using REs BstNI, StyI and MboI, respectively. The nucleotide sequences of STC, IN, Bursine 2 and Bio-Burs were determined at each of these sites. Nucleotide sequence analysis using this data and previously reported data for Del-E and Del-A was used to confirm the point mutation and predict the resulting amino acids. Although there were some exceptions, the BstNI and StyI enzymes detected point mutations in the first base of the 222 and 254 codons, respectively and could be used to predict an amino acid change in the viruses. MboI was detecting a mutation in the third base of codon 323 and could not reliably predict an amino acid change at that position. The results indicated that amino acids 222 and 254 were consistently mutated in the variant viruses examined and that amino acid 323 was not. Furthermore, point mutations resulting in amino acid changes at position 222 suggested that several groups of viruses may be defined by this site alone; proline for classic strains like STC, threonine for Del-E and GLS, serine for IN, Bursine 2, and Bio-Burs and glutamine for Del-A.

Animals↗
PubMed1998

Detection of codon 12 point mutations of the K-ras gene from mouse lung adenocarcinoma by 'enriched' PCR.

PURPOSE: Recent studies have shown that chemical carcinogens induce a high frequency of point mutations in the K-ras oncogene from mouse lung tumours at codons 12, 13 and 61. These experiments were performed to identify K-ras mutations in tissues from control and radiation-exposed mice. MATERIALS AND METHODS: By modifying the technique of the 'enriched' polymerase chain reaction (PCR), it was possible to detect point mutations at codon 12 of the K-ras oncogene from 25-year-old paraffin-embedded normal lungs and lung adenocarcinomas from mice exposed to radiation. Together, a total of 120 lung tissues were screened for point mutations at codon 12 of the K-ras oncogene in this study. RESULTS: A significant increase in K-ras codon 12 point mutations was observed in the normal lungs from mice exposed to 24 once-weekly neutron irradiations (100%), compared with normal lungs from mice with sham-irradiation (50%) (p<0.05). Lung adenocarcinomas from mice receiving 24 once-weekly neutron irradiations also had a significantly higher frequency of K-ras codon 12 point mutations (100%) than the lung adenocarcinomas of mice receiving 24 or 60 once-weekly gamma-ray irradiations (50%), but the higher frequency was not significantly different from that in spontaneous lung adenocarcinomas from mice (75%; p > 0.05). The validity of the technique was confirmed by sequencing two of the mutants. In doing so, a K-ras 13(Asp) point mutation was observed. CONCLUSIONS: The data suggest that high-linear energy transfer (LET) neutron radiation was more effective than low-LET gamma-rays in inducing K-ras point mutations at codon 12 in the lungs of B6CF1 mice.

Animals↗
PubMed1994

Overexpression and point mutations of p53 tumor suppressor gene in hepatocellular carcinomas in Hong Kong Chinese people.

BACKGROUND: Gene deletion, point mutations, and abnormalities in expression of the tumor suppressor gene p53 in hepatocellular carcinoma have been reported to occur with varying frequency in different geographic regions. METHODS: To assess the expression and point mutation of the p53 gene, 31 patients with hepatocellular carcinomas were examined using Northern blotting, immunohistochemical methods, and DNA sequencing. All patients were Chinese, and 90.3% were positive for hepatitis B surface antigen (HBsAg). RESULTS: p53 transcript or protein was found in 14 (48.4%) of the 31 patients. Detectable p53 mRNA transcripts were found in 10 patients, and p53 protein was detected in 8 patients. In most cases of patients who had detectable p53 mRNA transcripts, the transcripts in the tumors were exhibited at a higher level than they were in the corresponding nontumorous livers. No p53 protein was detected in the nontumorous livers in all 31 patients. Six (23.1%) of the 26 tumors sequenced showed point mutation scattered in exons 5-9. Of these, only two were at codon-249, and the nature of these two mutations was G-to-T transversions. All but one of the six patients with point mutations had overexpression of the gene. CONCLUSIONS: Our results show that scattered point mutations are not uncommon in hepatocellular carcinomas in patients from Hong Kong. The distribution pattern of the mutations seems to have no particular correlation with HBsAg status despite a high prevalence rate of HBsAg positivity in our patients. Consistent with a low aflatoxin exposure, aflatoxin-related specific mutation at codon-249 is much less related to the pathogenesis of hepatocellular carcinoma in Hong Kong Chinese people than in other regions with a high-aflatoxin exposure.

Adult↗
PubMed2001

Origin of the mutations in the parkin gene in Europe: exon rearrangements are independent recurrent events, whereas point mutations may result from Founder effects.

A wide variety of mutations in the parkin gene, including exon deletions and duplications, as well as point mutations, result in autosomal recessive early-onset parkinsonism. Interestingly, several of these anomalies were found repeatedly in unrelated patients and may therefore result from recurrent, de novo mutational events or from founder effects. In the present study, haplotype analysis, using 10 microsatellite markers covering a 4.7-cM region known to contain the parkin gene, was performed in 48 families, mostly from European countries, with early-onset autosomal recessive parkinsonism. The patients carried 14 distinct mutations in the parkin gene, and each mutation was detected in more than one family. Our results support the hypothesis that exon rearrangements occurred independently, whereas some point mutations, found in families from different geographic origins, may have been transmitted by a common founder.

Age of Onset↗
PubMed1995

[Low incidence of point mutation of N-ras oncogene in human gliomas].

We examined the incidence of point mutations in codon 12 and 61 of N-ras gene in human gliomas using PCR with mismatched primers. This method detects point mutations. PCR with mismatched primers induced restriction sites in normal DNA but not in mutational DNA. Genomic DNAs were extracted from paraffin-embedded tissues and were amplified with nested PCR. Among 17 cases, point mutation has not been able to be found so far, when examined in codon 12 of N-ras gene and among 10 cases in codon 61 of N-ras gene. It can thus be said that point mutational activation of N-ras oncogene is an uncommon event in human gliomas.

Base Sequence↗