Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “MUTATION”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 217 records · Page 12Linked to original sources
PubMed2002

Rapid mutation detection by the transgenomic wave analyser DHPLC identifies MYOC mutations in patients with ocular hypertension and/or open angle glaucoma.

AIMS: To rapidly screen Scottish patients with a family history of open angle glaucoma (OAG) or ocular hypertension (OHT) for mutations in the myocilin gene (MYOC) and develop a new rapid screening method for MYOC mutation detection. METHODS: All three exons of the MYOC gene were amplified by PCR from genomic DNA and subjected to direct DNA sequencing. Mutation detection methodology was also developed based on denaturing high performance liquid chromatography (DHPLC). A recurrent mutation was investigated by analysis of microsatellite haplotypes at the MYOC gene locus. RESULTS: Mutations were identified by DNA sequencing in four families. MYOC mutation Q368X was found in three kindreds and the fourth family carried the mutation G367R. The Q368X mutation was found to be associated with the same haplotype for markers closely flanking the MYOC gene. The mutations were identified by direct sequencing and were also readily detected by DHPLC analysis of PCR fragments, demonstrating that this is a robust method for MYOC analysis in future. CONCLUSIONS: Mutations in the MYOC gene were identified in patients presenting with highly variable phenotypes from normal through OHT to severe OAG. Haplotype analysis showed that mutation Q368X is likely to be an ancestral mutation in this population. DHPLC analysis is an accurate, rapid and cost effective method for MYOC mutation analysis in large population samples.

Adult↗
PubMed2004

Absence of PRSS1 mutations and association of SPINK1 trypsin inhibitor mutations in hereditary and non-hereditary chronic pancreatitis.

BACKGROUND AND AIMS: Mutations in the cationic trypsinogen (protease, serine, 1 (trypsin 1); PRSS1) gene are causally associated with recurrent acute and chronic pancreatitis. We investigated whether mutations in the PRSS1 gene are associated with hereditary and non-hereditary pancreatitis. As a modifier role has been proposed for trypsin inhibitor (serine protease inhibitor, Kazal type I; SPINK1) mutations, the role of SPINK1 mutations in these patients was also analysed. SUBJECTS AND METHODS: The coding regions of PRSS1 and SPINK1 genes were sequenced in 290 controls and 198 patients, of whom 120 were diagnosed as idiopathic (ICP), 41 as alcoholic (ACP), and 37 as hereditary pancreatitis (HP). Twenty four unaffected relatives of HP probands were also analysed and genotype-phenotype correlations and statistical analyses were performed. RESULTS: No mutations in the PRSS1 gene were detected in any of the patients, including HP patients, while the N34S mutation was observed in the SPINK1 gene in the majority of HP patients (73%). Similarly, 26.8% of ACP (11 of 41) and 32.5% (39 of 120) of ICP patients also had SPINK1 mutations. The N34S mutation was observed in both homozygous and heterozygous conditions. In comparison, only 2.76% of the control population had the N34S allele (p<0.001). The P55S mutation was observed in one ICP and one ACP patient, and in three normal individuals. Genotype-phenotype correlations did not suggest any significant difference in the age of onset, severity of disease, or pancreatic endocrine insufficiency in patients with or without mutated SPINK1 and irrespective of the allelic status of N34S SPINK1. CONCLUSIONS: Irrespective of the aetiology, mutations in the PRSS1 gene are not associated with chronic pancreatitis, including HP. In contrast, the N34S mutation in the SPINK1 gene shows a significant correlation in these patients. A comparable phenotype in terms of age of onset, diabetes mellitus, and other phenotypic features in patients with or without SPINK1 mutations and N34S homozygotes and heterozygotes suggests that there may still be involvement of other genetic or environmental factors.

Adult↗
PubMed2006

Analysis of p53 mutations for a mutational signature in human intrahepatic cholangiocarcinoma.

Cholangiocarcinoma development may be related to cholangiocyte DNA damage from genotoxic compounds in bile. We have previously shown that human biliary tissue is exposed to genotoxic agents, as evidenced by the presence of DNA adducts. Establishing the presence of a 'mutational signature' in tumour suppressor genes from tumour tissue provides a means of linking cause and effect in human cancer. Inactivation of p53, known to have 'hot-spots' for particular chemical carcinogens, has previously been linked to human cholangiocarcinoma. However, previous p53 studies have focused on exons 5-8, potentially missing gene alterations at other sites. This study examined the putative link between environmental carcinogens and intrahepatic cholangiocarcinoma by analysing DNA from 31 patients for complete p53 mutational signatures, using single strand conformational polymorphism and polymerase chain reaction. All mutations found were compared to known p53 mutations in cholangiocarcinoma and to mutations induced by environmental mutagens, as described in p53 databases. Five non-silent p53 mutations were found, including three new frameshift mutations and two new intron mutations which have not previously been reported in cholangiocarcinoma. Two frameshifts were due to deletions and the third due to an insertion in exon 5. There was no predominant mutational spectrum amongst the set of cholangiocarcinoma samples studied, or on combining these mutations with the dataset of known p53 mutations in cholangiocarcinoma. Several reasons may explain this, including lack of data outside exons 5-8, bias in mutation reporting, the involvement of mutations in non-coding regions or genes other than p53, or the possibility that there is no carcinogenic specific agent and therefore no signature.

Base Sequence↗
PubMed2006

Mutational analysis of RPGR and RP2 genes in Japanese patients with retinitis pigmentosa: identification of four mutations.

PURPOSE: To identify mutations in RPGR and RP2 genes in a series of Japanese retinitis pigmentosa (RP) families and to determine the association between the phenotypic changes in patients/carriers and the mutations. METHODS: A total of 37 unrelated RP families were recruited, three of which were with typical X-linked RP (XLRP), and other 34 families included 29 multiplex families and 5 simplex RP cases with no family history of RP. In addition, At least one RP patient had myopia >-3.0D in these families. RPGR and RP2 genes were comprehensively screened by using the direct polymerase chain reaction-sequencing method. Detailed phenotypes of the families with confirmed mutations were assessed by routine ophthalmic examinations, Goldmann perimetry, electroretinography and color fundus photography. RESULTS: Four mutations in RPGR and RP2 genes were identified. Of the three XLRP families, one had an ORF15 mutation and another had an RP2 mutation. Two ORF15 mutations were found in three of the other 34 RP families, with two families sharing a same mutation, g.ORF15+652-653delAG. All the three ORF15 mutations were first reported in the Japanese population. Affected males showed relatively severe symptoms while female carriers showed a wide spectrum of severity. A tapetal-like reflex was observed in two young females, indicating clinically the carrier status. CONCLUSIONS: We identified three ORF15 mutations and one RP2 mutation in five Japanese RP families. Moderate or severe myopia might be an indicator for the XLRP status in multiplex RP families which pedigree data are insufficient to allow accurate subtyping. It is suggested that mutational analysis of RPGR and RP2 may help to identify the causative mutation in a proportion of multiplex RP patients with myopia.

Adult↗
PubMed2003

Novel succinate dehydrogenase subunit B (SDHB) mutations in familial phaeochromocytomas and paragangliomas, but an absence of somatic SDHB mutations in sporadic phaeochromocytomas.

Phaeochromocytomas arising in adrenal or extra-adrenal sites and paragangliomas of the head and neck, in particular of the carotid bodies, occur sporadically and also in a familial setting. In addition to mutations in RET and VHL in familial disease, germline mutations in SDHD and SDHB genes that encode subunits of mitochondrial complex II have also been associated with the development of familial phaeochromocytomas. To further investigate the role of SDHD and SDHB in the development of these tumours we determined the occurrence of germline SDHD and SDHB mutations in four patients with a family history of phaeochromocytoma with associated head and neck paraganglioma, one patient with a family history of phaeochromocytoma only and two patients with apparently sporadic extra-adrenal phaeochromocytoma, one of whom had early onset disease. Secondly, we investigated whether somatic SDHB mutations correlated with loss of heterozygosity at 1p36 in a subgroup of 11 sporadic and three MEN 2-associated RET-mutation-positive phaeochromocytomas. Novel SDHB mutations were identified in the probands from four families and two apparently sporadic cases (six of seven probands studied), including two missense mutations, a single nonsense and frameshift mutation, as well as two splice site mutations, one of which was shown to have partial penetrance resulting in 'leaky' splicing. Further, five intronic polymorphisms in SDHB were found. No SDHD mutations were identified. In addition, no somatic SDHB mutations were found in the remaining allele of the 11 sporadic adrenal phaeochromocytomas with allelic loss at 1p36 or the three MEN 2-associated RET-mutation-positive phaeochromocytomas. Therefore, we conclude that SDHB has a major role in the pathogenesis of familial phaeochromocytomas, but the possible role of SDHB in sporadic tumours showing allelic loss at 1p36 has yet to be ascertained.

Adolescent↗
PubMed1997

Geographic distribution and regional origin of 272 cystic fibrosis mutations in European populations. The Biomed CF Mutation Analysis Consortium.

The geographic distribution of 272 cystic fibrosis (CF) mutations has been studied by assessing the origin of 27,177 CF chromosomes from 29 European countries and three countries from the North of Africa. The most common mutations are delta F308 (66.8%), G542X (2.6%), N1303K (1.6%), G551D (1.5%) and W1282X (1.0%). The delta F508 mutation has the highest frequency in Denmark (87.2%) and the lowest in Algeria (26.3%). Mutation G542X is common in the Mediterranean countries, with a mean frequency of 6.1%. N1303K is found in most of the western and Mediterranean countries and has the highest frequency in Tunisia (17.2%). The wide distribution of these mutations suggests an ancient origin. G551D is common in north-west and central Europe, but is uncommon in other parts of Europe. W1282X has the highest frequency in Israel (36.2%), being also common in most Mediterranean countries and north Africa. Seventeen mutation have frequencies between 0.1 and 0.9%, 1717-1G-->A (0.83%), R553X (0.75%), R1162X (0.51%), 621 + 1G-->T (0.54%) and 2183AA-->G (0.36%), being the most common ones. Some mutations reach relatively high frequencies in some extended geographic regions, such as mutation 394delTT in northern Europe (1.1-28.8%), R117H in northwestern Europe (1.3-3.0%), R553X in central Europe (1.1-24.4%), 1717-1G-->A in Belgium and France (1.1-5.3%), and 2183AA-->G in Italy and Greece (3.2%). Other mutations are only common in small regions: T338I (Sardinia), 711 + 1G-->T (Tunisia), R1162X (Algeria and north of Italy), 1609delCA (east of Spain), 1811 + 1.6kbA-->G (southeastern Spain), R1066C (Portugal), S549R (Algeria), R334W (Crete), 621 + 1G-->T (Central Greece), 3849 + 10kbC-->T (Israel), 2789 + 5G-->A (south of Greece), 451 + 1G--A (Israel), R347P (south of Bulgaria), 1677delTA (south of Bulgaria and Turkey), G85E (south of Greece), R347H (Turkey), 3905insT (Switzerland), 1078delT (Brittany), 1898 + 1G-->A (Wales), A455E (The Netherlands), delta I507 (Brittany), 3659delC (Sweden) and R560T (northern Ireland). Most of these mutations must have an origin and diffusion in the specific European population subgroup. Overall 55 mutations are common in one or several countries or regions of Europe and 217 mutations are rare with relative frequencies of lower than 1% in any of these regions and countries. This information might facilitate mutation analysis of CF in the different regions of Europe.

Africa, Northern↗
PubMed2000

Multidrug resistance genotypes (insertions in the beta3-beta4 finger subdomain and MDR mutations) of HIV-1 reverse transcriptase from extensively treated patients: incidence and association with other resistance mutations.

Multiple nucleoside resistance involves specific mutational patterns of the HIV-1 pol gene that are independent of the classic mutations conferring resistance to individual dideoxynucleosides. These include a cluster of five mutations in the reverse-transcriptase (RT) coding region (A62V, V75I, F77L, F116Y, and Q151M) generally referred to as multidrug resistance (MDR) mutations, and insertions of one or several amino acid residues between codons 67 and 70 of RT, a flexible region joining two antiparrallel beta sheets (beta3-beta4 insertions). The objectives of this study were (i) to determine the prevalence of multidrug resistance genotypes (MDR mutations and beta3-beta4 insertions) in a cohort of 632 patients who were extensively pretreated with anti-HIV drugs and not responding to their current antiretroviral therapy, and (ii) to analyze the association of multidrug resistance genotypes with other resistance mutations in the RT and protease genes. Among viruses sequenced from these patients, 15 (2.4%) of them contained an insertion and 2 (0.3%) contained a deletion in the beta3-beta4 finger subdomain of RT. In 9 cases, the insertion was associated with a D67S, G, or E mutation. In addition, we identified 13 (2.1%) viruses harboring specific MDR mutations (mainly Q151M and/or A62V, V75I, F116Y). Interestingly, the A62V mutation was found in 6 of the 15 strains with an insertion, whereas the other MDR mutations were not observed in insertion mutant strains. Especially high levels of resistance to zidovudine were observed for viruses with a beta3-beta4 insertion in the background of A62V, L210W, and T215Y. Otherwise, MDR mutations and beta3-beta4 insertions were found in association with the classic mutations conferring resistance to zidovudine, lamivudine, nonnucleoside RT inhibitors, and protease inhibitors, according to treatment history. Finally, we observed a genome with a deletion of codon 70 associated with a Q151M MDR mutation. These data suggest that the emergence of HIV-1 multidrug resistance, which may occur in various genetic contexts, poses a challenging problem in formulating treatment strategies.

Acquired Immunodeficiency Syndrome↗
PubMed1991

Ionizing radiation and genetic risks. III. Nature of spontaneous and radiation-induced mutations in mammalian in vitro systems and mechanisms of induction of mutations by radiation.

This paper (1) presents an analysis of published data on the molecular nature of spontaneously arising and radiation-induced mutations in mammalian somatic cell systems and (2) examines whether the molecular nature and mechanisms of origin of radiation-induced mutations, in mammalian in vivo and in vitro systems, as currently understood, are consistent with expectations based on the biophysical and microdosimetric properties of ionizing radiation. Depending on the test system (CHO cells, human T lymphocytes and human lymphoid cell line TK6), 80-97% of spontaneous HPRT mutations show normal Southern patterns; the remainder is due to gross changes, predominantly partial (intragenic) deletions. Total gene deletions at the HPRT locus are rare except in the TK6 cell line. At the APRT locus in CHO cells, 80-97% of spontaneous mutations are due to base-pair changes, the remainder being, mostly, partial deletions. The latter can extend upstream in the 5' direction but not beyond the APRT gene in the 3' direction. At the human HLA-A locus (T lymphocytes), the percentage of mutations with normal Southern patterns is lower than that for HPRT, and in the range of 50-60%. At the HLA-A locus, mitotic recombination contributes substantially to the mutation spectrum (approximately 30% of mutations recovered) and this is likely to be true of the TK locus in the TK6 cell line as well. With a few exceptions, most of the radiation-induced mutations show altered Southern patterns and are consistent with their being deletions and/or other gross changes (HPRT, 70-90% (CHO); 50-85% (TK6); 50-75% (T lymphocytes); TK, 60-80% (TK6); HLA-A, 80% (T lymphocytes); DHFR, 100% (CHO]. The exceptions are APRT mutations in CHO cells (16-20% of mutants with deletions or other changes) and HPRT mutations in T lymphocytes from A-bomb survivors (15-25%); the latter finding is consistent with the occurrence of in vivo selection against HPRT mutant cells. In cases of HPRT intragenic deletions analyzed (CHO cells and V79 Chinese hamster cells), there is evidence for a non-random distribution of breakpoints. The spontaneous mutation frequencies vary widely, from about 0.04/10(6) cells (sickle cell mutations at the human HBB locus) to 30.8/10(6) cells (HLA-A mutations in T lymphocytes) and are dependent on the locus, the system employed and a number of other factors. Those for the other loci fall between these limits.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2000

Evidence that error-prone DNA repair converts dibenzo[a,l]pyrene-induced depurinating lesions into mutations: formation, clonal proliferation and regression of initiated cells carrying H-ras oncogene mutations in early preneoplasia.

Initiation of skin tumors in mice is associated with the formation of oncogenic mutations in the H-ras gene. Mice treated on the dorsal skin with the potent polycyclic aromatic hydrocarbon (PAH) carcinogen dibenzo[a,l]pyrene (DB[a,l]P) form papillomas carrying the H-ras codon 61 (CAA to CTA) mutations. These mutations are induced in early preneoplastic skin within 1 day after DB[a,l]P treatment (Oncogene 16 (1998) 3203-3210) and appear to be related to DB[a,l]P-Ade-depurinating adducts (Proc. Natl. Acad. Sci. U. S. A. 92 (1995) 10422-10426). The rapid kinetics of mutation induction suggests that abasic sites generated from base depurination may undergo error-prone excision repair in pre-S-phase cells to induce these mutations. Analysis of mutations in the H-ras exon 1 and 2 region in DB[a,l]P-treated early preneoplastic skin indicated great changes in mutation spectra in the preneoplastic period. The initial spectra contained abundant A-->G mutations, which frequently occurred 3' to a putative conserved sequence (TGN-doublet). These mutations appeared to be induced initially as mismatched (G.T) heteroduplexes and then converted into double-stranded mutations by one round of replication. Unlike the A-->G mutations found in DB[a, l]P-treated skin (which forms 99% depurinating adducts), A-->G mutations found in anti-DB[a,l]P-diol epoxide-treated skin (forms 97% stable adducts) did not appear to be G.T heteroduplexes. These results, therefore, suggest that under these conditions, the repair errors occurred only from abasic sites but not from stable adducts. Initiated cells carrying specific oncogenic mutations, formed presumably by misrepair, underwent rapid clonal expansion and regression (transient clonoplasia). The multiplication of initiated stem cells during transient clonoplasia may be a factor determining the tumor-initiating potential of some PAH carcinogens.

Animals↗
PubMed1999

Multiple mutations in a shuttle vector modified by ultraviolet irradiation, (+/-)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene, and aflatoxin B(1) have different properties than single mutations and may be generated during translesion synthesis.

Shuttle vector-based systems are extensively employed to study the mutational properties of various mutagens in mammalian cells. Such vectors are designed for the detection of point mutations, that is small deletions and single base and tandem substitutions. However, mutant target genes carrying two or more point mutations, referred to as multiple mutations, can also be found in various proportions depending on the mutagen and the cells used. To evaluate the frequency and characteristics of multiple mutations, we used a system where the plasmid, pYZ289, was treated by ultraviolet irradiation, aflatoxin B(1) or (+/-)-7 beta,8 alpha-dihydroxy-9 alpha, 10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene before transfection into mouse fibroblast cells. The kinds of mutations and the mutational spectra were different for single and multiple mutations. In addition, in at least 75% of the cases, mutations of multiples appeared to arise in the same strand. Furthermore, mutational spectra for multiple mutations were different for 5' and 3' members of multiple sets. These observations suggest that multiple mutations arise via a different mechanism than single mutations. Moreover, these findings suggest that multiples arise during translesion DNA synthesis and involve an error-prone polymerase able to introduce a base opposite misinstructive or noninstructional DNA lesions and subject to subsequent misincorporation errors.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed2001

Haemophilia B mutations in Sweden: a population-based study of mutational heterogeneity.

The present series comprises all families (n = 77) with haemophilia B in Sweden and may be considered to be representative for the purposes of a population-based study of mutational heterogeneity. The 77 families (38 severe, 10 moderate, 29 mild) had 51 different mutations in total. Thirteen families had total, partial or small deletions, two had mutations in the promoter, eight families had splice site mutations, 14 had nonsense and the remaining 41 had missense mutations. Ten of the mutations, all C-->T or G-->A, recurred in 1--6 other families. Using haplotype analysis of seven polymorphisms in the factor IX (FIX) gene, we found that the 77 families carried 65 unique, independent mutations. Of the 48 families with severe or moderate haemophilia, 23 (48%) had a sporadic case of haemophilia compared with 31 families out of 78 (40%) in the whole series. Five of those 23 sporadic cases carried de novo mutations, 11 out of 23 of the mothers were proven carriers and, in the remaining seven families, it was not possible to determine carriership. Eleven of the 48 patients (23%) with severe haemophilia B developed inhibitors and all of them had deletions or nonsense mutations. Thus, 11 out of 37 (30%) patients with severe haemophilia B as a result of deletion/nonsense mutations developed inhibitors compared with 0 out of 11 patients with missense mutations. The ratio of male to female mutation rates was 5.3 and the overall mutation rate was 5.4 x 10(-6) per gamete per generation.

Age Factors↗
PubMed1999

Monilethrix: a novel mutation (Glu402Lys) in the helix termination motif and the first causative mutation (Asn114Asp) in the helix initiation motif of the type II hair keratin hHb6.

Monilethrix, a rare human hair disorder with autosomal dominant transmission, can be caused by mutations in hair keratins. Up to now, causative mutations have only been found in two type II cortex keratins, hHb6 and hHb1. In these hair keratins, the helix termination motif, HTM, was the only site in which mutations were located. The most frequent mutation, which has been found in 22 cases, was a Glu413Lys substitution in hHb6, whereas other mutations, i.e., hHb6 Glu413Asp, hHb1 Glu413Lys, and hHb1 Glu402Lys, have been reported in a distinctly lower number of cases. In this study, we describe the equivalent of the hHb1 Glu402Lys mutation in the HTM of cortex keratin hHb6. The mutation occurred in an American family in which it could only be detected in one clinically affected individual. Thus the underlying G-->A transition represents a spontaneous germ-line mutation in the hHb6 gene. This new mutation indicates that both the hHb6/hHb1 Glu413Lys substitution and the hHb6/hHb1 Glu402Lys substitution, represent mutational hotspots in the HTM of type II cortex keratins. However, we also describe a monilethrix-causing mutation in the helix initiation motif, HIM, of the cortex keratin hHb6. The critical Asn114Asp substitution was only found in affected members of a large Swedish three-generation family. Considering that since childhood, half of the affected individuals suffer from complete baldness and follicular keratosis, the new HIM mutation seems to be associated with a rather severe disease phenotype. In conclusion, our data strongly suggest that monilethrix is a disease of the hair cortex, whose etiology is interesting in that causative mutations seem to be restricted to type II hair keratins.

Amino Acid Sequence↗
PubMed1995

Adaptive mutations in Escherichia coli as a model for the multiple mutational origins of tumors.

The cells in most tumors are found to carry multiple mutations; however, based upon mutation rates determined by fluctuation tests, the frequency of such multiple mutations should be so low that tumors are never detected within human populations. Fluctuation tests, which determine the cell-division-dependent mutation rate per cell generation in growing cells, may not be appropriate for estimating mutation rates in nondividing or very slowly dividing cells. Recent studies of time-dependent, "adaptive" mutations in nondividing populations of microorganisms suggest that similar measurements may be more appropriate to understanding the mutation origins of tumors. Here I use the ebgR and ebgA genes of Escherichia coli to measure adaptive mutation rates where multiple mutations are required for rapid growth. Mutations in either ebgA or ebgR allow very slow growth on lactulose (4-O-beta-D-galactosyl-D-fructose), with doubling times of 3.2 and 17.3 days, respectively. However, when both mutations are present, cells can grow rapidly with doubling times of 2.7 hr. I show that during prolonged (28-day) selection for growth on lactulose, the number of lactulose-utilizing mutants that accumulate is 40,000 times greater than can be accounted for on the basis of mutation rates measured by fluctuation tests, but is entirely consistent with the time-dependent adaptive mutation rates measured under the same conditions of prolonged selection.

Adaptation, Physiological↗
PubMed2000

APC mutations in sporadic colorectal tumors: A mutational "hotspot" and interdependence of the "two hits".

Although APC mutations occur at a high frequency in colorectal cancers, few studies have performed a comprehensive analysis by screening the whole gene for mutations and assessing allelic loss. APC seems to act as a tumor-suppressor gene in a "nonclassical" fashion: data from familial adenomatous polyposis (FAP) show that the site of the germ-line mutation determines the type of "second hit" in FAP tumors, and simple protein inactivation is selected weakly, if at all. In this study, we screened the entire coding region of APC for mutations and assessed allelic loss in a set of 41 colorectal cancer cell lines. Of 41 cancers, 32 (83%) showed evidence of APC mutation and/or allelic loss. We identified several APC mutations and found a "hotspot" for somatic mutation in sporadic colorectal tumors at codon 1,554. Our results suggest that APC mutations occur in the great majority of colorectal cancers, the exceptions almost all being RER+ tumors, which may substitute for altered APC function by mutations in beta-catenin and/or at other loci. When combined with previously published data, our results show that there is interdependence of the "two hits" at APC in sporadic colorectal tumors as well as in FAP. APC mutations in the "mutation cluster region," especially those close to codon 1,300, are associated with allelic loss, whereas tumors with mutations outside this region tend to harbor truncating mutations. The causes of this phenomenon are probably selection for retained N-terminal and lost C-terminal APC functions, effects on beta-catenin levels, and APC protein stability.

Base Sequence↗
PubMed1999

Beneficial mutations, hitchhiking and the evolution of mutation rates in sexual populations.

Natural selection acts in three ways on heritable variation for mutation rates. A modifier allele that increases the mutation rate is (i) disfavored due to association with deleterious mutations, but is also favored due to (ii) association with beneficial mutations and (iii) the reduced costs of lower fidelity replication. When a unique beneficial mutation arises and sweeps to fixation, genetic hitchhiking may cause a substantial change in the frequency of a modifier of mutation rate. In previous studies of the evolution of mutation rates in sexual populations, this effect has been underestimated. This article models the long-term effect of a series of such hitchhiking events and determines the resulting strength of indirect selection on the modifier. This is compared to the indirect selection due to deleterious mutations, when both types of mutations are randomly scattered over a given genetic map. Relative to an asexual population, increased levels of recombination reduce the effects of beneficial mutations more rapidly than those of deleterious mutations. However, the role of beneficial mutations in determining the evolutionarily stable mutation rate may still be significant if the function describing the cost of high-fidelity replication has a shallow gradient.

Alleles↗
PubMed2003

Estimating mutation rate: how to count mutations?

Mutation rate is an essential parameter in genetic research. Counting the number of mutant individuals provides information for a direct estimate of mutation rate. However, mutant individuals in the same family can share the same mutations due to premeiotic mutation events, so that the number of mutant individuals can be significantly larger than the number of mutation events observed. Since mutation rate is more closely related to the number of mutation events, whether one should count only independent mutation events or the number of mutants remains controversial. We show in this article that counting mutant individuals is a correct approach for estimating mutation rate, while counting only mutation events will result in underestimation. We also derived the variance of the mutation-rate estimate, which allows us to examine a number of important issues about the design of such experiments. The general strategy of such an experiment should be to sample as many families as possible and not to sample much more offspring per family than the reciprocal of the pairwise correlation coefficient within each family. To obtain a reasonably accurate estimate of mutation rate, the number of sampled families needs to be in the same or higher order of magnitude as the reciprocal of the mutation rate.

Humans↗
PubMed2001

Holoprosencephaly due to mutations in ZIC2: alanine tract expansion mutations may be caused by parental somatic recombination.

We report on the prevalence of mutations in the zinc finger transcription factor gene, ZIC2, in a group of 509 unrelated individuals with isolated holoprosencephaly (HPE) and normal chromosomes. Overall, we encountered 16 HPE patients (from 15 unrelated families) with ZIC2 mutations. Thus, ZIC2 mutation was the apparent cause of HPE in 3-4% of cases. Seven mutations were frameshifts that were predicted to result in loss of function, further supporting the idea that ZIC2 haploinsufficiency can result in HPE. One mutation, an alanine tract expansion which is caused by the expansion of an imperfect trinucleotide repeat, occurred in seven patients from six different families. In three of those families, the father was found to be apparently mosaic for the mutation. We hypothesize that this mutation can arise through errors in somatic recombination, an extremely unusual mutation mechanism. In addition, one mutation resulted in a single amino acid change and one mutation was an in-frame deletion of 12 amino acids. The central nervous system malformations seen in patients with ZIC2 mutations ranged from alobar HPE (most common) to middle interhemispheric fusion defect (one case). Although severe facial anomalies are common in HPE, all of the patients with ZIC2 mutations had relatively normal faces, suggesting that ZIC2 mutations represent a large proportion of HPE cases without facial malformation.

Alanine↗
PubMed1993

Low frequencies of somatic mutation in two expressed V kappa genes: unequal distribution of mutation in 5' and 3' flanking regions.

Somatic mutation of antibody variable region genes is a hallmark of secondary responses. Most often the coexpressed VH and V kappa genes of a B cell mutate at nearly equal rates. We have previously identified hybridomas from two B cell clones that exhibited > 10-fold lower frequency of mutation in their expressed V kappa 12 or V kappa 1A genes relative to their coexpressed VH genes. To gain insight into the mechanism(s) responsible for this low frequency V kappa mutation, we determined the frequency of mutation in non-coding flanking DNA from multiple members of each clone. We find a low frequency of mutation in the 5' (4/700) and 3' (1/670) non-coding regions of the expressed V kappa 1A genes consistent with the low frequency of coding region mutation. In contrast, the distribution and frequency of mutation surrounding the expressed V kappa 12.37 gene are unusual. Among the six members of this clone there are 31 mutations 3' (31/2100 bp) and no mutations 5' (0/2010 bp) of the V kappa exon. This V kappa exon has acquired mutations that are intermediate in number to its flanking regions and are significantly skewed in distribution to the 3' end. None of the 31 3' mutations are shared by two or more members of this clone, indicating that they all occurred late in clonal expansion. These results raise the possibility that some V kappa genes may lack functional cis-regulatory elements which direct V kappa coding region mutation.

Animals↗