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PubMed2002

X-linked Charcot-Marie-Tooth disease caused by a novel point mutation in the connexin-32 gene.

We report the clinical and electrophysiological findings of a patient with X-linked Charcot-Marie-Tooth disease and a novel point mutation in the connexin-32 gene. A 31-year-old man presented with a 5 year history of progressive imbalance and distal weakness in his legs. Electrophysiological studies confirmed an asymmetric, predominantly axonal sensorimotor neuropathy with some demyelinating features. Genetic testing revealed a G/A transition (Ala40Thr) in a conserved transmembrane region of the connexin-32 gene.

Adult↗
PubMed1997

c-kit Point mutation in patients with myeloproliferative disorders.

Myeloproliferative disorders (MPD) constitute a group of hematopoietic neoplasms at the myeloid stem cell level. Myeloid stem cells and/or progenitor cells from MPD have been considered sensitive to hematopoietic growth factors, including erythropoietin, thrombopoietin and stem cell factor (SCF). SCF is a ligand for c-kit receptor with tyrosine kinase. We analysed the gene alteration of the c-kit extracellular domain in MPD patients by PCR-SSCP and subsequent nucleotide sequencing. The point mutation in the N-terminal part of the domain, codon 52 (Asp-->Asn), was found in two patients with primary myelofibrosis and one with chronic myelogenous leukemia. We review the literature regarding the role of SCF/c-kit system in the oncogenesis of leukemia and MPD, and then discuss the significance of our finding in the context of growth advantage of the mutated clones over the normal clones.

Adult↗
PubMed1995

Detection of point mutations in human tyrosinase gene by improved allele-specific amplification.

Allele-specific amplification (ASA) is a simple and non-radioactive technique for detecting known point mutations that produce genetic diseases. Although this technique is based on the specific amplification of the target allele by a polymerase chain reaction (PCR) with allele-specific primers, the specificity of the amplification may depend on various PCR conditions. To avoid non-specific amplification which leads to false-positive results in ASA, we modified both the normal and mutant allele-specific primers so that they would have one constant base mismatch, located at the penultimate 3' position. We confirmed that our modification could inhibit such unfavorable amplification by using as templates genomic DNAs of patients affected with tyrosinase-negative oculocutaneous albinism (OCA). We then analyzed new patients affected with tyrosinase-negative OCA, and based the diagnosis on both the results of a clinical examination and those of a hair bulb test using ASA with the modified allele-specific primers. The results indicated that more than 3 alleles of the tyrosinase gene with a pathological mutation existed in Japanese patients.

Albinism, Oculocutaneous↗
PubMed1993

Defects of neuronal migration and the pathogenesis of cortical malformations are associated with Small eye (Sey) in the mouse, a point mutation at the Pax-6-locus.

The mouse Small eye (Sey) locus is situated on chromosome 2. Molecular analyses have shown that SeyNeu represents a point mutation leading to a splice site error and loss of the functional gene product. The Sey locus has been shown to be identical with the paired box (Pax)-6 gene, which contains paired-like and homoeobox domains and is a developmental control gene. Pax-6 expression occurs in many parts of the central nervous system during embryogenesis. Therefore, we may expect the Sey mutation to result in abnormal development of the central nervous system. The present study shows that Pax-6 mutation has a bimodal effect upon neurogenesis in mouse: it causes a delay of premigratory neurons in a stage-, region-, and gene-dose-dependent manner. Additionally, Sey mutation impairs axonal growth and differentiation. Neurons of the cortical plate cease differentiation on approximately day 16 of gestation and appear to have increased cohesion: their cytoplasm is swollen and vacuolated. These changes coincide both with reduced formation of axons and with the onset of vacuolar degeneration in existing axons, glial cells and radial glial fibers. Consequently, there is an impairment of the peripheral migration of putative neurons so that the neonatal lesion pattern of the neocortical roof becomes dominated by a broad spectrum of neuronal migration disorders.

Animals↗
PubMed1998

Molecular epidemiology of malaria in Yaoundé, Cameroon. III. Analysis of chloroquine resistance and point mutations in the multidrug resistance 1 (pfmdr 1) gene of Plasmodium falciparum.

It has been postulated that chloroquine resistance may be associated with a single point mutation at codon 86 of the Plasmodium falciparum multidrug resistance 1 (pfmdr 1) gene. Using a simple and rapid molecular technique involving polymerase chain reaction and restriction fragment length polymorphism, the frequency of the Asn-to-Tyr mutation associated with chloroquine resistance was established among 129 clinical isolates obtained from indigenous patients in Yaoundé, Cameroon. The results showed that 110 of 129 isolates display a mutant codon. The other clinical isolates had either a pure wild-type Asn-86 codon (n = 12) or mixed Asn/Tyr alleles (n = 7). In vitro drug assays were performed to compare the genotype and phenotype in 102 clinical isolates. Of these isolates, 86 displayed pure Tyr-86 mutant codon; 48 (56%) mutant isolates were chloroquine-resistant (50% inhibitory concentration [IC50] > 100 nM), as expected, but 38 (44%) mutant isolates were chloroquine-sensitive (IC50 < 100 nM). Three chloroquine-resistant isolates and seven chloroquine-sensitive parasites carried a wild-type Asn-86 codon. Mixed alleles were found in six isolates (four chloroquine-sensitive and two chloroquine-resistant isolates). Our results did not confirm previous observations on the possible association between chloroquine resistance phenotype and genotype based on the pfmdr 1 gene.

ATP-Binding Cassette Transporters↗
PubMed2006

[Prediction of the possible tertiary structure alterations of p53 protein following point mutation in p53 gene condon 282 in lung cancer cells].

This study was carried out to predict the possible tertiary structure alterations of p53 protein after point mutation of p53 gene condon 282 in lung cancer cells based on the latest 3D structure analysis platform series of Phyre software. It was found that the p53 gene condon 282 mutation (Arg/Leu) may destabilize the H2 helix and DNA binding in the major groove by compromising the contacts of p53 protein with the beta-hairpin of DNA binding surface.

Amino Acid Sequence↗
PubMed2005

Genetic and functional characterization of the Escherichia coli BarA-UvrY two-component system: point mutations in the HAMP linker of the BarA sensor give a dominant-negative phenotype.

The BarA-UvrY two-component system family is strongly associated with virulence but is poorly understood at the molecular level. During our attempts to complement a barA deletion mutant, we consistently generated various mutated BarA proteins. We reasoned that characterization of the mutants would help us to better understand the signal transduction mechanism in tripartite sensors. This was aided by the demonstrated ability to activate the UvrY regulator with acetyl phosphate independently of the BarA sensor. Many of the mutated BarA proteins had poor complementation activity but could counteract the activity of the wild-type sensor in a dominant-negative fashion. These proteins carried point mutations in or near the recently identified HAMP linker, previously implicated in signal transduction between the periplasm and cytoplasm. This created sensor proteins with an impaired kinase activity and a net dephosphorylating activity. Using further site-directed mutagenesis of a HAMP linker-mutated protein, we could demonstrate that the phosphoaccepting aspartate 718 and histidine 861 are crucial for the dephosphorylating activity. Additional analysis of the HAMP linker-mutated BarA sensors demonstrated that a dephosphorylating activity can operate via phosphotransfer within a tripartite sensor dimer in vivo. This also means that a tripartite sensor can be arranged as a dimer even in the dephosphorylating mode.

Dimerization↗
PubMed2005

The residue E351 is essential for the activity of human 21-hydroxylase: evidence from a naturally occurring novel point mutation compared with artificial mutants generated by single amino acid substitutions.

Congenital adrenal hyperplasia (CAH) [OMIM 201910] is a group of autosomal recessive disorders, caused in 90-95% of cases by a deficiency of steroid 21-hydroxylase due to mutations in the CYP21A2 gene. The functional and structural effects of a novel rare missense mutation (E351K) in CYP21A2 found in a male patient with simple virilizing CAH were studied. The novel E351K point mutation is located in the ERR triad of the 21-hydroxylase. The ERR triad is a glutamine-arginine-arginine motif conserved in all cytochrome P450 sequences. The glutamate and first arginine residue are invariant in all P450 cytochrome enzymes, whereas the second arginine residue is present as arginine, histidine, or asparagine. Although the ERR triad is involved in some way to heme binding by the cytochrome P450 monooxygenases, the E351K mutation leads to severe but not complete loss of CYP21 enzyme activity. The functional analysis in COS-7 cells revealed a reduced conversion of 17-hydroxyprogesterone to 11-deoxycortisol of 1.1+/-0.5% (SD) and of progesterone to 11-deoxycorticosterone of 1.2+/-0.3% of wild-type activity. Analyzing the artificial mutants (E351D, E351I) of the E351 residue did not show a restoration of the in vitro 21-hydroxylase activity. These effects could be readily explained by structural changes induced by the mutations, which were rationalized by a three-dimensional-model structure of the CYP21 protein. The combination of in vitro enzyme function and computerized protein analysis of the E351 residue of the CYP21 protein provides experimental evidence for the ERR triad being a fundamental structural element of cytochrome P450 enzymes.

Amino Acid Substitution↗
PubMed1996

[Detection of K-ras point mutations in the stool of patients with colorectal tumors].

Using mutant-allele-specific amplification procedure, patients with colorectal tumors were analyzed for K-ras point mutations in the stool and the tumor tissue. K-ras mutation of DNA purified from the stool was detected in 10 of 40 (25.0%) cancer patients, and in 3 of 10 (30.0%) adenoma patients. Otherwise, in the cases whose tumors contained the mutations, it was detected with the frequency of 71.4% in cancers, and 100% in adenomas. This frequency tended to decrease in the cancers of distal colon or small size, but there was no significant. This study suggested that stool analysis of genetic alterations would develop diagnostic method for colorectal cancer.

Adult↗
PubMed1999

Familial atrial septal defect and atrioventricular conduction disturbance associated with a point mutation in the cardiac homeobox gene CSX/NKX2-5 in a Japanese patient.

Atrial septal defect (ASD) is the most common form of congenital cardiac defect in humans. Recently, point mutations in the cardiac homeobox gene CSX/NKX2-5 have been reported to cause the autosomal dominant form of familial ASD. Notably, all the affected patients exhibit atrioventricular conduction disturbance and some of them died suddenly. The first case of familial ASD with a mutation of the CSX/NKX2-5 gene in a Japanese patient is reported here. Identification of CSX/NKX2-5 mutations in ASD patients would be very important because the existence of such mutations may predict sudden cardiac death.

Heart Block↗
PubMed1996

Point mutation analysis of archived cytogenetic slide DNA.

Archived Giemsa-stained cytogenetic slide repositories represent valuable DNA resources for medical, scientific, and forensic studies. Sequencing readily identified a Charcot-Marie-Tooth disease point mutation in a 209-bp PCR amplified product. With optimal PCR primers and amplification conditions, our protocol quickly and reliably isolated sufficient DNA for at least 12 independent PCR amplification reactions for forensic and medical applications from single slides up to 5 years old.

Alleles↗
PubMed2002

A simple method of detecting K-ras point mutations in stool samples for colorectal cancer screening using one-step polymerase chain reaction/restriction fragment length polymorphism analysis.

BACKGROUND: We examined a technique for detecting point mutations of K-ras codon 12 in stool samples using one-step polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP) analysis, in order to determine whether it could be used to screen for colorectal cancer. METHODS: DNA was extracted from 200-mg stool specimens of 5 healthy controls and 31 colorectal cancer patients. A 107-base-pair fragment of exon 1 of K-ras was amplified by PCR using mismatched primers. PCR products were digested with Bst NI and analyzed by gel electrophoresis followed by silver staining. Specificity of one-step PCR/RFLP was examined by using synthetic oligonucleotides. The detection limit of K-ras codon 12 mutations was determined by using SW480 and HT29 cells. RESULTS: The K-ras gene was successfully amplified from all healthy controls and colorectal cancer patients studied. Mutations of K-ras codon 12 were not detected in any of the healthy controls, but were identified in 13 (41.9%) of the 31 patients with colorectal cancer. Mutations were detectable in all six synthetic mutant DNAs, while none were detected among the wild type. The detection limit of this method was > or = 0.1%. CONCLUSIONS: PCR/RFLP analysis could be used in mass screening for colorectal cancer, because it is highly specific, has a low detection limit, and is simpler than conventional methods for detecting genetic abnormalities.

Adult↗
PubMed2001

Association of a novel point mutation (C159G) of the CTLA4 gene with type 1 diabetes in West Africans but not in Chinese.

Here, we report on the detection of a novel point mutation of the CTLA4 gene at nucleotide position 159 (C-->G) leading to amino acid substitution at position 53 (I-->M), as well as its association with type 1 diabetes in two ethnically distinct populations. Subjects included 182 unrelated type 1 diabetes children and 201 control subjects from Ghana, West Africa. The Chinese study population consisted of 350 type 1 diabetic children and 420 healthy control subjects from central China. Polymerase chain reaction-single-strand conformation polymorphism and sequence analysis were used to screen for polymorphisms in the CTLA4 gene. CTLA4 49 (A-->G) mutation conferred a risk of type 1 diabetes in the Chinese children (odds ratio 1.78, 95% CI 1.58-2.0), but not in the West African children (1.17, 0.84-1.64). On the other hand, the novel CTLA4 159 (C-->G) mutation conferred a risk of type 1 diabetes in the West African children (2.1, 1.54-2.86), but not in the Chinese type 1 diabetic children. The novel CTLA4 gene polymorphism at nucleotide position 159 significantly associated with type 1 diabetes in West Africans, but not in Chinese. On the other hand, the CTLA4 gene polymorphism at nucleotide position 49 significantly associated with type 1 diabetes in Chinese, but not in West Africans.

Abatacept↗
PubMedDate not supplied

Distribution of some point mutations in the phenylalanine hydroxylase gene of phenylketonuria patients from the Moscow region.

Thirty-one unrelated phenylketonuria patients from the Moscow region were screened for mutations in the phenylalanine hydroxylase gene at the following codons: 408, 158, 261 and IVS-12. For detection of point mutations, polymerase chain reaction amplification was applied with allele-specific oligonucleotide hybridization. The following mutation frequencies were determined: codon 408-56.4%; codon 158-8.1%; codon 261-3.2%, and IVS-12-16%.

Base Sequence↗
PubMed2003

Melas with point mutations involving tRNALeu (A3243G) and tRNAGlu(A14693g).

The syndrome of mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episode (MELAS) is typically associated with a single point mutation in the mitochondrial genome (mtDNA). Because mtDNA is known to have a higher mutation rate than nuclear DNA, we speculate that some patients with MELAS syndrome may harbor more than one mutation in mtDNA. For this purpose, mtDNA extracted from muscle containing dysmorphic mitochondria from a 32-year-old man with MELAS was sequenced in its entirety to identify all possible mutations. The result showed a homoplasmic A14693G and a heteroplasmic A3243G. The A14693G transition was not present in 205 unrelated control individuals, was not seen in 76 species randomly selected from GenBank, and appears to disrupt the base pairing within the T-loop of mtDNA tRNA(Glu). His asymptomatic siblings' blood showed wild-type at these positions, whereas the blood of the patient's oligosymptomatic diabetic mother had a heteroplasmic A14693G and an apparent homoplasmic wild-type A3243, suggesting an association of A14693G with diabetes mellitus. This case demonstrates the importance of sequencing the mtDNA in its entirety to evaluate the molecular basis of mitochondriopathy.

Adult↗
PubMed2006

Two point mutations of RPE65 from patients with retinal dystrophies decrease the stability of RPE65 protein and abolish its isomerohydrolase activity.

RPE65 is the isomerohydrolase in the retinoid visual cycle essential for recycling of 11-cis retinal, the chromophore for visual pigments in both rod and cone photoreceptors. Mutations in the RPE65 gene are associated with inherited retinal dystrophies with unknown mechanisms. Here we show that two point mutations of RPE65, R91W and Y368H, identified in patients with retinal dystrophies both abolished the isomerohydrolase activity of RPE65 after a subretinal injection into the Rpe65-/- mice and in the in vitro isomerohydrolase activity assay, independent of their protein levels. Further, the R91W and Y368H mutants showed significantly decreased protein levels but unchanged mRNA levels when compared with the wild-type RPE65 (wtRPE65). Protein stability analysis showed that wtRPE65 is a fairly stable protein, with an apparent half-life longer than 10 h, when expressed in 293A cells. Under the same conditions, mutants R91W and Y368H both showed substantially decreased protein stabilities, with half-lives less than 2 and 6 h, respectively. Subcellular fractionation and Western blot analysis demonstrated that wtRPE65 predominantly exists in the membrane fraction, while both of the mutants are primarily distributed in the cytosolic fraction, suggesting that these mutations disrupt the membrane association of RPE65. However, palmitoylation assay showed that wtRPE65 and both of the mutants were palmitoylated. These results suggest that these mutations may result in critical structural alterations of RPE65 protein, disrupt its membrane association, and consequently impair its isomerohydrolase activity, leading to retinal degeneration.

Animals↗
PubMed2004

Identification of a novel point mutation in the RET gene (Ala883Thr), which is associated with medullary thyroid carcinoma phenotype only in homozygous condition.

The RET protooncogene mutations responsible for multiple endocrine neoplasia type 2 are inherited as autosomic dominant traits. We describe here a novel germline homozygous mutation in exon 15 of the RET gene that determines an amino acid substitution (Ala->Thr) at codon 883. The index case was a 51-yr-old patient with an apparently sporadic form of medullary thyroid cancer (MTC). RET gene mutations screening was performed in exons 10, 11, 13, 14, 15, and 16 by automatic sequence analysis. An unexpected homozygous GCT->ACT point mutation was found at codon 883 in exon 15 and confirmed by restriction analysis (Alu I). The presence of the two chromosomes 10 was confirmed by fluorescence in situ hybridization analysis on lymphocytes. As expected on the basis of the homozygosity of the index case, the parents were consanguineous (second-degree cousins). Eight relatives were further investigated: the mother, two sisters, and the son were positive for heterozygous RET mutation. The mother (82 yr old) showed a nodular goiter but was negative both for basal and pentagastrin stimulated calcitonin. The young son (15 yr old) and the two sisters (63 and 58 yr old) did not show any clinical and/or biochemical sign of MTC. One brother (59 yr old) was negative both for RET mutation and clinical/biochemical examination. The other brother, 56 yr of age, was positive for both homozygous RET mutation and serum calcitonin. When operated, the histological examination of the thyroid showed the presence of MTC and C cell hyperplasia. In conclusion, we identified a new germline RET gene mutation during a routine RET gene screening of an apparently sporadic MTC case. This mutation showed a very low transforming activity as demonstrated by the absence of MTC phenotype in heterozygous subjects. The possibility that the homozygous gene carriers were indeed carrying a germline loss of heterozygosity was excluded by fluorescence in situ hybridization analysis for RET gene performed on lymphocytes derived from one homozygous patient. The analysis of several RET polymorphisms also confirmed the presence of two mutated alleles in MTC affected patients and both mutated and wild-type allele in heterozygous subjects.

Carcinoma, Medullary↗
PubMed1997

Variable levels of a heteroplasmic point mutation in individual hair roots.

During direct sequencing of the first hypervariable segment of the human mitochondrial control region, we identified one individual with a heteroplasmic point mutation at nt 16,256. We used primer extension to analyze the proportions of each mitochondrial haplotype in peripheral blood, buccal cells, and single hair roots from this individual and from eight members of his maternal lineage. Significant levels of heteroplasmy were found in only three individuals, and, in these cases, the proportions of each haplotype were similar in both blood and buccal cells. From the changes in mitochondrial haplotypes within mother-offspring pairs, we calculated that the most likely size of a mitochondrial bottleneck during development was 1-27 segregating units. However, highly variable levels of heteroplasmy were found in single hair roots, even among roots from the same individual. We analyzed a large number of hair roots from one individual and found that the proportion of one haplotype was within a range of 9% to > 99% in different roots. Roots originating from within a small patch of skin had haplotype proportions as variable as those from different areas of skin.

DNA, Mitochondrial↗