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PubMedDate not supplied

Carrier detection in DMD families with point mutations, using PCR-SSCP and direct sequencing.

Non-isotopic single-strand conformation polymorphism (SSCP) and direct sequencing was used for carrier diagnosis in four families of DMD/BMD patients with previously characterized point mutations, leading to the identification of eight carriers and four non-carriers. When the mutation caused a distinctly altered migration pattern of the single strands, in principle, the SSCP-technique allowed determination of carrier status in the extended family of the probands without direct sequencing. However, because SSCP measures a function of not only the mutation, but of the entire sequence of the PCR product, it can lead to false negative and/or false positive diagnoses due to intronic and exonic sequence heterogeneity in the family. As we discovered this pitfall in one of the reported families, we concluded that for carrier testing the SSCP approach must be performed in essential conjunction with an independent assessment of the mutation site by direct sequencing.

Adult↗
PubMed1999

Deletions and point mutations of p16,p15 gene in primary tumors and tumor cell lines.

Aberrations of chromosome 9 p21-22 are involved in the genesis of many forms of cancer. The gene p16 and p15 have been assigned to this region. Both p16 and p15 are an inhibitor of cyclin D-cdk4,cyclin D-cdk6 complex and have been implicated in a wide variety of cancer types, including the germline of patients with familial melanoma. In order to investigate and compare the status of p16,p15 gene in primary tumors and cell lines, we examined 357 primary tumors and 29 cell lines derived from diverse tumor types. In addition to analysis of these primary tumors and cell lines, blood specimens from 91 patients either with sporadic multiple cancers or from cancer-prone families were also analyzed. The data showed the following: 1) Homozygous deletions of p16,p15 were comparatively rare and far less common than previously reported, although hemizygous deletions were observed in a significant fraction of many tumor types; 2) the incidence of p16,p15 deletions (either homozygous deletions or heterozygous deletions) varied significantly among different tumor types; 3) most deletions involved in both p16 and p15 genes; 4) sequence variations in the coding sequence of p16,p15 were comparatively rare among these tumor types, though mutations and polymorphisms were identified; 5) some tumors which showed LOH at 9p, containing p16 and p15 gene, did not show deletions or point mutations in the p16,p15 gene. 6) In a subset of retinoblastoma and osteosarcoma where no Rb gene mutations were present a significant fraction was found to contain p16,p15 gene deletions.

Bone Neoplasms↗
PubMed1999

Suppression of inward-rectifying K+ channels KAT1 and AKT2 by dominant negative point mutations in the KAT1 alpha-subunit.

The Arabidopsis thaliana cDNA, KAT1 encodes a hyperpolarization-activated K+ (K+in) channel. In the present study, we identify and characterize dominant negative point mutations that suppress K+in channel function. Effects of two mutations located in the H5 region of KAT1, at positions 256 (T256R) and 262 (G262K), were studied. The co-expression of either T256R or G262K mutants with KAT1 produced an inhibition of K+ currents upon membrane hyperpolarization. The magnitude of this inhibition was dependent upon the molar ratio of cRNA for wild-type to mutant channel subunits injected. Inhibition of KAT1 currents by the co-expression of T256R or G262K did not greatly affect the ion selectivity of residual currents for Rb+, Na+, Li+, or Cs+. When T256R or G262K were co-expressed with a different K+ channel, AKT2, an inhibition of the channel currents was also observed. Voltage-dependent Cs+ block experiments with co-expressed wild type, KAT1 and AKT2, channels further indicated that KAT1 and AKT2 formed heteromultimers. These data show that AKT2 and KAT1 are able to co-assemble and suggest that suppression of channel function can be pursued in vivo by the expression of the dominant negative K+in channel mutants described here.

Animals↗
PubMed2002

Single point mutation in the Rieske iron-sulfur subunit of cytochrome b6/f leads to an altered pH dependence of plastoquinol oxidation in Arabidopsis.

The pgr1 mutant of Arabidopsis thaliana carries a single point mutation (P194L) in the Rieske subunit of the cytochrome b6/f (cyt b6/f) complex and is characterised by a reduced electron transport activity at saturating light intensities in vivo. We have investigated the electron transport in this mutant under in vitro conditions. Measurements of P700 reduction kinetics and of photosynthetic electron transport rates indicated that electron transfer from cyt b6/f to photosystem I is not generally reduced in the mutant, but that the pH dependence of this reaction is altered. The data imply that the pH-dependent inactivation of electron transport through cyt b6/f is shifted by about 1 pH unit to more alkaline pH values in pgr1 thylakoids in comparison with wild-type thylakoids. This interpretation was confirmed by determination of the transmembrane deltapH at different stromal pH values showing that the lumen pH in pgr1 mutant plants cannot drop below pH 6 reflecting most likely a shift of the pK and/or the redox potential of the oxidised Rieske protein.

Arabidopsis↗
PubMed2001

DNA sequence analysis of protein S deficiency--identification of four point mutations in twelve Japanese subjects.

The molecular basis for the hereditary type I protein S (PS) deficiency was investigated. DNA sequence analysis of 12 patients with PS deficiency in Japan identified four point mutations and three of them were novel. Nonsense mutations found in two unrelated patients resulted in termination of the PS polypeptide chains at Gln 238 and Lys 392, respectively. Two novel missense mutations were also found in two other patients substituting Asp 202 for Asn and Leu 298 for Pro, respectively. Comparison of the PS amino acid sequences from several mammalians indicated that Asp 202 and Leu 298 were preserved and thus appeared to be responsible for the pathogenesis of PS deficiency.

Humans↗
PubMed1996

Disruption of the NAD(+)-specific glutamate dehydrogenase gene of Neurospora crassa by means of the RIP (repeat-induced point mutations) process.

The structural gene for the catabolite-repressed, substrate-induced NAD(+)-specific glutamate dehydrogenase (gdh-1) of Neurospora crassa was disrupted using the process of repeat-induced point mutation (RIP). Plasmids containing incomplete copies of the gene, along with selectable markers, were introduced into germinated conidia by electroporation. The sexual progeny of a transformant containing an ectopically integrated copy of a plasmid, harbouring the 5' flanking region and a part of the coding sequence of gdh-1 DNA, was examined for the occurrence of RIP by (i) Southern blot analysis of the genomic DNA digested with the isoschizomers MboI and Sau3A, (ii) Northern blot analysis of total RNA in cultures subjected to repression and induction conditions for NAD-GDH, (iii) direct assessment of enzymatic activity, and (iv) evaluation of protein levels by Western blot analysis using a polyclonal anti-GDH IgG preparation. Attempts were made at delineating different regions of the gene exhibiting RIP by using 32P-labelled DNA probes, corresponding to (i) the complete gene, (ii) a fragment containing the 5' flanking region plus two-thirds of the coding sequence, and (iii) the 5' flanking segment alone. The extent and relative location of RIP, as revealed by these hybridization probes, appeared to correlate with changes in specific activity under repression and derepression conditions. Mutant progeny, thus recovered, included isolates with altered regulatory features, such as constitutive expression, inability to elicit derepression, higher-than-wildtype GDH levels under derepression and inefficient repression.

Blotting, Northern↗
PubMed1993

[Studies on the point mutation of ras oncogene in ovarian tumor].

Thirty-five patients with ovarian tumors operated on between December, 1989 and June, 1991 were studied to detect K-ras codon 12 point mutation (PM). (1) Five of 35 ovarian tumors (14.3%) disclosed K-ras PM at codon 12 and all the PM cases were in transition from GGT to GAT. On the other hand only one case (5.3%) with K-ras oncogene amplification was found and no C-myc or erbB-2 amplification was detected. (2) The incidence of PM according to clinical stages was seen in 3 of 11 stage I cases (27.3%), in 1 of 3 stage II cases (33.3%), in 1 of 14 stage III cases (7.1%) and in neither of 2 stage IV cases. PM was therefore seen in relatively early stages. (3) The occurrence of PM according to the histologic type was found in 3 of 16 serous tumors (18.8%), in 2 of 5 mucinous tumors (40.0%) and in none of 7 clear cell carcinomas or 2 endometrioid carcinomas. (4) Concerning the relation of PM to the involvement of serosal surface of ovarian tumors and to the ascitic cytology, no particular correlation was observed in our study. (5) Regarding the cytologic findings in imprint smears of the tumors in reference to PM, such as nuclear size, shape, N/C ratio, chromatin pattern, nucleolar size and number, the cases with PM tended to have more multiple nucleoli than PM negative cases. No other findings seemed to indicate the clinical progress of cancer. In conclusion, our study indicated that PM in ovarian cancers was a relatively early event in carcinogenesis.

Adult↗
PubMed2003

alpha-globin gene deletion and point mutation analysis among in Iranian patients with microcytic hypochromic anemia.

We tested 67 Iranian individuals, presenting with low mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH) levels, normal hemoglobin electrophoresis and iron status, for the presence of twelve common alpha-thalassemia gene deletions and point mutations. Five different mutations (-alpha(3.7), -alpha(4.2), --MED, -(alpha)20.5, Hb Constant Spring) were identified in a total of 43 cases

Anemia, Hypochromic↗
PubMed1999

Activated protein C (APC)-resistance: automated detection of the point mutation at position 1691 in the factor V gene.

Proteolytic cleavage of factor Va, caused by activated protein C, is an important mechanism in limiting clot formation in normal haemostasis. A single point mutation in the factor V gene has been demonstrated to cause resistance of factor Va to proteolytic cleavage by activated protein C. With an 8-fold increased risk of thrombosis and a 2 to 13% prevalence in the Caucasian population for the heterozygous state of this mutation, knowledge of the patient's genetic disposition is of great importance in conditions such as pregnancy, surgery, use of oral contraceptives and immobilization. Therefore we have developed an automated test for the detection of the factor V mutation. This PCR based test makes use of the disappearance of an Mnl 1 restriction site if the mutation is present. The assay has been developed for the widely used ES-systems of Boehringer Mannheim. The test discriminates between the heterozygous and the homozygous state. Because of its low costs and easy handling the assay can be used as a screening test and can be performed in routine clinical laboratories.

Activated Protein C Resistance↗
PubMed2001

[Human obesity and point mutations of leptin and leptin receptor].

Obesity-related genes were isolated and identified in these several years. Development of transgenic mice has clarified the molecular mechanisms of obesity. There have been reported point mutations of the genes correspond to leptin(ob-gene) and leptin receptor(db-gene). Thereby leptin is considered to be one of the most important regulators of energy metabolism also in human.

Animals↗
PubMed1988

Optically detected magnetic resonance study of tyrosine residues in point-mutated bacteriophage T4 lysozyme.

Two spectroscopically distinct types of tyrosine (Tyr) residues in triply point mutated bacteriophage T4 lysozyme, which contains no tryptophan (Trp), have been detected by optical detection of triplet-state magnetic resonance (ODMR) spectroscopy. Their triplet states are characterized by similar E but different D values. The Tyr site which exhibits the lower D value and has the red-shifted phosphorescence origin is quenched by energy transfer to Trp and has D and E values comparable to previously studied Tyr residues. The blue-shifted Tyr site, which is not quenched by Trp, exhibits a larger D value that has been found previously. Calculation of energy-transfer efficiencies of Tyr-Trp pairs based on the crystal structure of the native enzyme provides a possible assignment of Tyr sites to the two different spectral types.

Magnetic Resonance Spectroscopy↗
PubMed1988

Characterization of point mutations in the same arginine codon in three unrelated patients with ornithine transcarbamylase deficiency.

Point mutations in the X-linked ornithine transcarbamylase (OTC) gene have been detected at the same Taq I restriction site in 3 of 24 unrelated probands with OTC deficiency. A de novo mutation could be traced in all three families to an individual in a prior generation, confirming independent recurrence. The DNA sequence in the region of the altered Taq I site was determined in the three probands. In two unrelated male probands with neonatal onset of severe OTC deficiency, a guanine (G) to adenine (A) mutation on the sense strand (antisense cytosine [C] to thymine [T]) was found, resulting in glutamine for arginine at amino acid 109 of the mature polypeptide. In the third case, where the proband was a symptomatic female, C to T (sense strand) transition converted residue 109 to a premature stop. These results support the observation that Taq I restriction sites, which contain an internal CG, are particularly susceptible to C to T transition mutation due to deamination of a methylated C in either the sense or antisense strand. The OTC gene seems especially sensitive to C to T transition mutation at arginine codon 109 because either a nonsense mutation or an extremely deleterious missense mutation will result.

Adult↗
PubMed1992

[Activation of protooncogenes by point mutations in hematological malignancies].

The activation of protooncogenes (ras, fms and myc genes) by point mutations in hematological malignancies are described in this review. Ras mutations are found in a variety of human malignancies at codon 12, 13, and 61. Generally, N-ras mutations are frequent in hematological malignancies. Fms mutation at codon 301 and 969, which are seen in 10 to 20% cases of AML and MDS, increase tyrosine kinase activity of the fms products. Ras and fms mutations are postulated to influence leukemogenesis at rather early stages. Burkitt lymphomas are characterized by specific chromosomal translocations between c-myc gene and one of the immunoglobulin genes. Furthermore, mutations in the 3' border of the exon 1 of c-myc are frequent, and may play an additional role in pathogenesis of Burkitt lymphoma.

Animals↗
PubMed1993

Genetic screening in Saccharomyces cerevisiae for large numbers of mitochondrial point mutations which affect structure and function of catalytic subunits of cytochrome-c oxidase.

A new search for mitochondrial respiratory deficient mutants (Mit-) has been undertaken in order to accumulate a large number of point mutations in the coding portions of cytochrome-c-oxidase catalytic subunits and cytochrome b. Therefore, a mitochondrial DNA which retains the exons and lacks all the introns of the cytochrome oxidase subunit I and of the cytochrome-b split genes has been introduced into a strain carrying a nuclear recessive mutation affecting the adenine-nucleotide translocator, the op1 mutation, which is known to prevent the accumulation of large deletion petite mutants and this was used as the parental strain. After a moderate MnCl2 mutagenesis in order to limit multiple mutations, 105 Mit- mutants were isolated from 15,000 mutagenised clones in Saccharomyces cerevisiae. Mutations were mapped to the three catalytic subunits encoding genes (COX1, COX2 and COX3) of the cytochrome-c oxidase (70 mutations) and to the cytochrome-b gene (15 mutations). More than 50% of the mutants tested still exhibited mitochondrial translation products (subunits I, II and III), suggesting that they carry a missense mutation, rather than a nonsense mutation which would normally have led to a truncated protein. Mutations in the COX1 gene were allocated to four different subregions corresponding to exons 4 and 8 or to groups of exons, exons 1, 2, 3 or exons 5, 6, 7. Seven missense monosubstitution mutations and two frameshift mutations were also identified. The amino acid changes of the missense mutations were located in the vicinity of the CuB-heme alpha 3 binuclear centre ligands.

Amino Acid Sequence↗
PubMed1998

Two novel slavic point mutations in the low-density lipoprotein receptor gene in patients with familial hypercholesterolemia from St. Petersburg, Russia.

Using PCR-single-strand conformation polymorphism analysis, followed by sequencing of the abnormal samples, two novel point mutations in the 5' end of the fourth exon of the low-density lipoprotein receptor gene were found in two Russian families with familial hypercholesterolemia. These missense mutations consist of C127W and C139G transitions and result in a loss of one of three disulfide bonds in the fourth cysteine-rich repeat of the ligand-binding domain of the low-density lipoprotein receptor. Hypercholesterolemia segregated with the identified mutations.

Adolescent↗
PubMed2006

A point mutation at the calreticulin gene core promoter conserved sequence in a case of schizophrenia.

Exposure to atypical antipsychotic drugs such as valproate increases the expression of chaperones that assist in the folding of proteins in the endoplasmic reticulum (ER) including calreticulin, GRP78/BiP, GRP94, and PD1. This neuroprotective role may be involved in the pathophysiology of neuropsychiatric disorders such as schizophrenia and bipolar disorder. The 5'-flanking region of the human calreticulin gene was screened in 100 cases of schizophrenia by PCR/SSCA between -485 and +1 basepair (bp) relative to the transcription start site. A G > C point mutation was detected at -48 in a case of paranoid schizophrenia, which was not detected in 280 unrelated control subjects (560 chromosomes). This is the first report of mutation in relation with the calreticulin gene. The -48G > C mutation creates a CpG site at the core promoter region of the gene. The role of this mutation remains to be clarified in the pathophysiology of the disease.

Adult↗
PubMed1995

Cysteine-to-arginine point mutation in a 'hybrid' eight-cysteine domain of FBN1: consequences for fibrillin aggregation and microfibril assembly.

Mutations in the FBN1 gene encoding the microfibrillar glycoprotein fibrillin cause Marfan syndrome, a relatively common autosomal dominant connective tissue disease. Causative FBN1 mutations appear to be dispersed throughout the coding frame, and to date no predictable genotype: phenotype correlations have emerged. We have identified a point mutation within an eight-cysteine 'hybrid' motif of the fibrillin polypeptide which results in the substitution of an arginine for a cysteine, in a patient severely affected in the cardiovascular, skeletal and ocular systems. We have utilised cell cultures from various tissues of this patient to investigate the effects of this mutation on fibrillin expression and deposition, and the consequences in terms of microfibril assembly and organisation. We have established that there is no difference in the expression of normal and mutant alleles, and fibrillin synthesis, secretion and deposition are also normal. However, the rate of fibrillin aggregation is reduced and microfibrillar assemblies are both remarkably scarce and morphologically abnormal. These data clearly demonstrate that the mutated allele interferes with normal assembly, and strongly implicate this particular region of the fibrillin-1 molecule in stabilising microfibrillar assemblies.

Actin Cytoskeleton↗