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At least 289 records · Page 16Linked to original sources
PubMed2000

Structural characterization of a new variant of the CYP2A6 gene (CYP2A6*1B) apparently diagnosed as heterozygotes of CYP2A6*1A and CYP2A6*4C.

During the course of investigating the frequency of a CYP2A6 whole deletion-type polymorphism (CYP2A6*4C) in Japanese, an unexpectedly large population of heterozygotes for CYP2A6*4C and the wild-type (CYP2A6*1A) was found. Cloning of a cDNA encoding CYP2A6 from the liver of individuals judged as heterozygotes for CYP2A6*4C and the CYP2A6*1A was carried out to identify the causal allele(s) responsible for a possible overestimation. A clone isolated from the liver cDNA library possessed 58 bp sequences in the 3'-untranslated region, which was replaced with the corresponding region of the CYP2A7 gene. The same gene conversion existed in the genomic DNA, indicating that the replacement was not a cloning artifact. Based on the gene structure of the allele (CYP2A6*1B), this variant was thought to be one of the causal alleles responsible for overestimation of heterozygotes for CYP2A6*4C and CYP2A6* A. To investigate this further, we developed a genotyping method which could distinguish the CYP2A6*A, CYP2A6*1B and CYP2A6*4C alleles from each other. The results clearly showed that CYP2A6*1B was the sole allele responsible for the overestimation. We conclude that the new genotyping method allows determination of six genotypes of the CYP2A6 gene, simultaneously and precisely, in both Oriental and Caucasian populations.

3' Untranslated Regions↗
PubMed1997

Risk of mother-to-infant transmission of HIV-1 is not reduced in CCR5/delta32ccr5 heterozygotes.

To determine if the 32-bp deletion of the chemokine receptor CCR5 (delta32ccr5) protects against mother-to-infant transmission of HIV-1, specimens from all uninfected and infected children who were perinatally exposed to HIV-1 and observed since 1988 and whose mothers did not take zidovudine were assessed for delta32ccr5. The CCR5 genotype was determined using polymerase chain reaction (PCR) for 122 subjects, of whom 73 were HIV-1 infected and 49 were perinatally exposed but uninfected; 70% and 71%, respectively, were Caucasian. Eleven of 73 (15%) infected children and 4 of 49 (8%) exposed uninfected children were CCR5/delta32ccr5 heterozygotes (p = 0.40). Among subjects who had at least one Caucasian parent or grandparent, 11 of 51 (22%) HIV-1-infected persons and 4 of 35 (11%) uninfected persons were heterozygotes. None were homozygous for the delta32ccr5 allele. The estimated relative risk for mother-to-infant HIV-1 transmission in heterozygotes was 2.0. Furthermore, the 95% confidence interval (0.6, 7.3) suggested that it is unlikely that the true relative risk was <0.6. Thus, the infant CCR5/delta32ccr5 heterozygous genotype was not associated with a diminished risk of perinatally acquired HIV-1 infection.

Alleles↗
PubMed2003

Analysis of secondary V(D)J rearrangements in mature, peripheral T cells of ataxia-telangiectasia heterozygotes.

Ataxia-telangiectasia (AT) is a rare recessive disease with pleiotropic involvement of the nervous and lymphoid systems. AT heterozygotes have a population frequency of about 1%, and although not manifesting any overt clinical symptoms, they have an increased mortality, mainly because of cancer and ischemic heart disease. We and others have described a mature T lymphocyte population with an altered T cell receptor surface expression ("TCR variant") that reactivates the recombination activating genes (RAG) and is expanded in the blood of patients with AT. In view of the known role of V(D)J recombination in the onset of tumorigenic translocations, we proposed that the increased RAG activity was responsible for the predisposition of AT homozygotes to develop mature-type T leukemia/lymphoma. In the present report, we used cytofluorimetry to quantify the TCR variant population and the memory/naïve T-cell compartments in the blood of AT heterozygotes compared with AT patients and controls. We assessed the expression of different recombinase genes through RT-PCR/oligotyping and cytofluorometric analysis and searched for rearrangement intermediates by ligase-mediated PCR in T-cell lines from four heterozygous carriers. We found the TCR variant population was increased on average 2x in AT heterozygotes (vs 10x in homozygotes) compared with controls, and naïve CD4(+) T lymphocytes were reduced on average 0.5x (vs 0.1x in homozygotes). We were able to demonstrate recombinase gene expression in all four heterozygous T-cell lines, and rearrangement intermediates, indicative of ongoing V(D)J recombination, in two. These rearrangements were compatible with V-gene replacement, a mechanism of receptor editing described for Ig and TCRalpha genes, to our knowledge not previously documented for TCRbeta. In conclusion, we found that RAG reactivation and secondary V(D)J rearrangements, potential risk factors of mature-type leukemia in AT homozygotes, also take place in AT heterozygous carriers and might place this large population fraction at an increased risk of leukemia/lymphoma.

Ataxia Telangiectasia↗
PubMed1993

Absence of DNA repair deficiency in the confirmed heterozygotes of xeroderma pigmentosum group A.

This study was performed to elucidate whether xeroderma pigmentosum complementation group A (XPA) carrier has DNA repair abnormality against sun-exposure and ultraviolet (UV)-mimetic chemical carcinogen 4-nitroquinoline 1-oxide (4NQO). Here we report three sporadic cases of XP that were defined as group A by genetic complementation test as well as polymerase chain reaction (PCR) analysis to detect the point mutation in the responsible gene for XPA. DNA repair analyses in the skin fibroblasts revealed that the cells from the patients were much more sensitive to UV and 4NQO and had extremely low UV-induced unscheduled DNA synthesis (UDS) than control cells, whereas the cells from the carriers (heterozygotes of XP) had sensitivity to UV and 4NQO and levels of UV-induced UDS similar to normal cells. These results indicate that the obligate heterozygotes, despite having a mutated allele in XPA complementing gene demonstrated by PCR, have no DNA repair abnormality after UV irradiation and UV-mimetic 4NQO treatment. Our observations imply that XPA heterozygotes do not have higher risk of skin cancers than normal subjects based on their DNA repair abnormality.

4-Nitroquinoline-1-oxide↗
PubMed2006

Heterozygote excess in a self-incompatible and partially clonal forest tree species -- Prunus avium L.

Wild cherry (Prunus avium L.), a partially asexual self-incompatible forest tree, shows heterozygote excess, which is a poorly studied phenomenon. In three natural populations, we found significant heterozygote excess at almost all investigated loci (eight microsatellites and markers for the self-incompatibility locus). We examined four hypotheses to account for this observed heterozygote excess. First, negative F(IS) can result from a lack of selfed progeny in small populations of outcrossing species. A second explanation for negative F(IS) is selection during the life cycle of the most heterozygous individuals. A third explanation is negative assortative mating when reproduction occurs between individuals bearing phenotypes more dissimilar than by chance. The last explanation for negative F(IS) relies on asexual reproduction. Expectations for each hypothesis were tested using empirical data. Patterns of F(IS) differed among loci. Nevertheless, our experimental results did not confirm the small sample size hypothesis. Although one locus is probably under a hitch-hiking effect from the SI locus, we rejected the effect of the self-incompatibility locus for the genome as a whole. Similarly, although one locus showed a clear pattern consistent with the selection of heterozygous individuals, the heterosis effect over the whole genome was rejected. Finally, our results revealed that clonality probably explains significant negative F(IS) in wild cherry populations when considering all individuals. More theoretical effort is needed to develop expectations and hypotheses, and test them in the case of species combining self-incompatibility and partially asexual reproduction.

France↗
PubMed1991

Rumpshaker: an X-linked mutation affecting CNS myelination. A study of the female heterozygote.

This study examines the myelin deficits found in the spinal cord and optic nerves of female mice heterozygotes for rumpshaker (rsh), an X-linked mutation causing hypomyelination. No clinical abnormalities were detected but morphological changes were evident, particularly in the spinal cord, which showed no evidence of resolving with age. In the spinal cord, scattered hypomyelinated axons, occasionally grouped in twos or threes, were the major feature; oligodendrocyte numbers were slightly elevated at all ages compared to normal male littermates and the total amount of myelin was reduced. Myelin protein composition of the sheaths was examined by immunostaining for myelin basic protein (MBP) and two peptide regions of PLP/DM-20 molecule; one being proteolipid protein (PLP)-specific and the other recognizing the c-terminal common to PLP-DM-20. The majority of myelin sheaths immunostained for MBP and PLP. Occasional MBP-positive sheaths failed to stain with PLP/DM-20 or PLP-specific antiserum. Therefore, at least two types of immunocytochemically-defined myelin sheaths are present in the heterozygotes. Changes in the optic nerves were much less obvious; glial cell numbers were increased but thinly myelinated axons were not detected although the total amount of myelin was reduced compared to normal littermates. In no instance were mosaic, amyelinated/hypomyelinated patches detected. Heterozygotes for rsh, therefore, are considerably different from those for other X-linked myelin mutations like the jimpy mouse and the myelin-deficient rat, both in regard to the severity of the lesions and their failure to recover with age.

Animals↗
PubMed1976

Carcinoembryonic antigen and cystic fibrosis protein in blood from cystic fibrosis homozygotes and heterozygote carriers.

Carcinoembryonic antigen (CEA) activity was measured by radioimmunoassay in blood from cystic fibrosis (CF) homozygotes, heterozygote carriers of CF, normal healthy controls, and other patient controls with carcinomas involving gastrointestinal organs. All samples were also screened by electrofocusing for cystic fibrosis protein (CFP), a metabolic marker previously shown to be associated with the CF gene. Significantly increased levels of CEA activity were found in all CFP-positive groups; however, with one exception all patient controls with marked increases in CEA activity were CFP-negative. Immunodiffusion of perchloric acid extracts of CEA-like material from heterozygote carrier blood indicated that the CEA-like material, which was elevated in homozygotes and heterozygotes for CF, showed only partial identity with two separate CEA preparations obtained from colon carcinomas and was not identical to either A, B, or O(H) blood group substances. This glycoprotein material did, however, react with three different anti-CEA antisera. Our finding of an abnormally increased glycoprotein in cystic fibrosis, taken together with previous reports demonstrating abnormalities in the carbohydrate portion of glycoproteins found in various exocrine secretions in CF, further suggests that the primary defect in this disease is manifested partly as a defect in glycoprotein metabolism. This defect may result from an abnormality in one or more of the glycosyltransferases, possibly caused by a more primary defect in polyamine metabolism.

Adolescent↗
PubMed1977

Serum pancreatic isoamylases in the diagnosis of cystic fibrosis heterozygotes: A non-valuable test.

A group of 102 obligate heterozygotes for the cystic fibrosis gene were examined for genetic type of pancreatic isoamylases as well as enzyme activity of pancreatic iso-amylases, salivary isoamylases and total amylase in serum. The analysis was performed using electrophoretic separation for detection of the various types of isoamylases, and their relative activity was determined by means of densitometry. The activities of salivary isoamylases and total amylase in serum showed no significant differences between the cystic fibrosis heterozygotes and a control group. The frequency of the variant gene for pancreatic isoamylase was also the same as in the controls. The mean value for pancreatic isoamylase was slightly higher in the cystic fibrosis heterozygotes than in the control group (0.05 greater than P greater than 0.02).

Adult↗
PubMed1991

Absence of DRw15/3 and of DRw15/7 heterozygotes in Caucasian patients with systemic lupus erythematosus.

Polymorphic MHC class II molecules determine immune responsiveness towards pathogens and also contribute to susceptibility or resistance to a number of different autoimmune diseases, including systemic lupus erythematosus (SLE). The HLA-DR and -DQ alleles of 52 patients with SLE were analyzed by serology and, for 42 patients, HLA-DRB1, -B3 and DQB1 allelic polymorphism was determined by oligotyping on PCR-amplified DNA. While we confirm the increase of DR3 (44.2% versus 16% in controls; p less than 0.001) reported by others, we observed a complete absence of DRw15(2)/DR3 and DRw15(2)/DR7 heterozygotes among Caucasian patients. Moreover HLA-DQB1 oligotyping revealed the absence of DQB1*0602/0201 heterozygotes in our panel of Caucasoid SLE patients. Since both DR3 and DR7 haplotypes share the same DQB1*0201-encoded DQ beta chain, and since DRw15 is known to be in linkage disequilibrium with DQA1*0102, it can be predicted that DQA1*0102/DQB1*0201 combinations are absent in Caucasian patients. We therefore propose that a DQA1*0201/DQB1*0201-encoded HLA-DQ trans-dimer formed in these heterozygotes might function as a suppressor-inducer molecule that confers resistance against SLE.

Blotting, Southern↗
PubMed1985

Cystic fibrosis heterozygotes have normal autonomic innervation of the heart.

Five simple tests of autonomic nerve function based on measurements of cardiovascular responses to various stimuli were used to investigate possible autonomic dysfunction in obligate heterozygotes for cystic fibrosis. There were no significant differences between the heterozygotes and control groups in any of the tests, suggesting that cystic fibrosis heterozygotes have normal autonomic innervation of the heart.

Adult↗
PubMed1975

Detection of homozygotes and heterozygotes for metachromatic leukodystrophy in lymphoid cell lines and peripheral leukocytes.

Assays of arylsulphatase A have been performed on peripheral leukocytes and lymphoid cell lines from normal subjects and heterozygotes and homozygotes for metachromatic leukodystrophy (MLD) by utilizing an improved procedure based on the removal of excess protein from the final digest. No overlap of arylsulphatase A activity was observed between peripheral leukocytes obtained from 11 normal donors, 8 heterozygotes and 5 homozygotes for MLD. Absence of enzyme activity was demonstrated in the patients' leukocytes, when the modified assay procedure was employed. Arylsulphatase A activity (mean +/- S.D.) in 30 lymphoid lines and sublines established from 18 normal donors, 2 heterozygotes and 1 homozygote for MLD was 54-5 +/- 23-1, 24-1 +/- 3-2 and 0-9, respectively. The enzymic activity of arylsulphatase A and B remained stable over a period of several months. These findings indicate that long-term lymphoid lines express the genotype of the donor and maintain enzyme stability over long periods in culture. Moreover, it appears that peripheral leukocytes are a reliable system for the identification of the carrier state of MLD.

Animals↗
PubMed1974

Expression of the familial hypercholesterolemia gene in heterozygotes: mechanism for a dominant disorder in man.

Studies in ctltured fibroblasts indicate that the primary genetic abnormality in familial hypercholesterolemia involves a deficiency in a cell surface receptor for low density lipoproteins (LDL). In normal cells, binding of LDL to this receptor regulates cholesterol metabolism by suppressing cholesterol synthesis and increasing LDL degradation. In cells from heterozygotes, a 60 percent reduction in LDL receptors leads to a concentration-dependent defect in regulation, so that attainment of equal rates of cholesterol synthesis and LDL degradation in normal and heterozygous cells requires a two- to threefold higher concentration of LDL in the heterozygote. The identification of this genetic regulatory defect in fibroblasts of heterozygotes makes available an in vitro system for studying the effects of a dominant mutation on gene expression in mammalian cells.

Alcohol Oxidoreductases↗
PubMed1972

Bactericidal action of streptomycin and comparison with spectinomycin in heterozygotes of Escherichia coli.

Str(s)/str(r) heterozygotes of Escherichia coli K-12 are shown to be sensitive to the lethal as well as the inhibitory action of streptomycin. The rate of killing was lower in heterozygotes than in sensitive homozygotes, and among heterozygotes it was lower in those with a higher proportion of resistant ribosomes. These strains also differed, in a parallel manner, in the kinetics of inhibition of growth and protein synthesis by streptomycin. Similar results were obtained with spectinomycin and corresponding merodiploid strains. Since spectinomycin is purely bacteriostatic and stabilizes polysomes, it must block resistant ribosomes behind inhibited sensitive ribosomes; hence, these results are consistent with an initial similar polysomal blockade by streptomycin. However, since streptomycin causes gradual polysome breakdown, its dominant lethal action must involve some mechanism other than a permanent polysomal blockade.

Antibiotics, Antineoplastic↗
PubMed1998

Heterozygotes for HFE mutations have no increased risk of advanced alcoholic liver disease.

BACKGROUND: Iron overload is common in the livers of alcoholics and may play a role in disease pathogenesis. An MHC like gene, HFE, has recently been identified that is mutated in most patients with hereditary haemochromatosis (C282Y in 90% and H63D in 45% of the remainder). AIM: To examine the hypothesis that these mutations determine hepatic iron status in alcoholics and play a role in pre-disposition to advanced alcoholic liver disease. METHODS: The HFE gene was genotyped in 257 patients with alcoholic liver disease and 117 locally matched healthy volunteers. In addition, iron staining was scored (0-4) on biopsy specimens from fibrotic/cirrhotic patients with and without HFE mutations matched for age and sex. RESULTS: Some 15.7% of fibrotic/cirrhotic patients were C282Y heterozygotes compared with 13.7% of controls (p = 0.77). One control and three patients were C282Y homozygotes. Of chromosomes without the C282Y mutation, 68/442 (15.4%) of patients' chromosomes carried the H63D mutation compared with 36/216 (16.6%) of control chromosomes (p = 0.91). Significant (> grade 1) hepatocyte iron staining was seen in 6/23 C282Y heterozygotes and 4/26 H63D heterozygotes compared with 4/23 controls. CONCLUSIONS: Possession of a single copy of either of the two HFE mutations influences neither liver iron content nor the risk of fibrotic disease in alcoholics.

Enzyme-Linked Immunosorbent Assay↗
PubMed1977

Heterozygote advantage for the phenylketonuria allele.

Mean weight at birth of unaffected (normal homozygous and PKU heterozygous) offspring of parents heterozygous for the phenylketonuria (PKU) allele averages significantly above that of Norwegian neonates, with no significant difference in mean age of mothers or in mean parity. It approaches the optimal birthweight--that which confers the minimum overall mortality in the pre-, peri-, and postnatal periods. This near-optimal birthweight together with the possibly higher effective fertility observed in PKU heterozygous couples (at least in those who married before 1940), has apparently more than outweighed the disadvantages of the allele in PKU homozygous offspring as shown, for example, in an excessive number of pre- and perinatal deaths among the total offspring of PKU heterozygotes, to say nothing of the PKU survivors who, often, used to die young. The two effects--fertility and viability--apparently both contribute in the same direction, to give a biological fitness in excess of 1 for the heterozygote. This heterozygote advantage presumably explains the presence of the allele at frequencies above those to be expected from the simple replacement of a homozygously-lethal allele by mutation alone.

Alleles↗
PubMed1985

Admission of Hb S heterozygotes to a general hospital is relatively reduced in malarial areas.

A comparison between the frequency of Hb S heterozygotes in blood donors, outpatients, and inpatients of a general hospital carried out at the Maputo Central Hospital, Mozambique, where Plasmodium falciparum malaria is endemic, showed a statistically significant lower percentage of Hb S heterozygotes in the inpatient group. Evidence is thus provided that the protection given by Hb S to heterozygotes concerns not only malarial infection itself, but probably a wide spectrum of diseases to which persons who have a special resistance to P falciparum infection are less prone.

Anemia, Sickle Cell↗
PubMed1970

Early recognition of heterozygotes for the gene for dystrophia myotonica.

A study has been performed on 124 first degree relatives of 38 index patients with dystrophia myotonica in order to assess means of detecting heterozygotes before neurological complaints. Some or all of the following tests have been performed on the relatives: clinical examination, electromyography, slit-lamp examination, radiography of the skull, electrocardiography, serum insulin, and serum immunoglobulin levels. There is evidence that abnormalities in symptomless heterozygotes may be detected by slit-lamp examination, electromyography, and immunoglobulin concentration, and this is probably the order of usefulness of the test in early recognition of the disease. In this study 13 previously undetected heterozygotes have been identified: six as a result of neurological examination, four by both electromyography and slit-lamp examination, and three by slit-lamp examination alone. Abnormalities detected by these tests appear to be independently manifest, so that they will probably be more useful in combination than singly. The family data give a maximum estimate for incidence of mutations among index cases of one quarter, lower than previously suggested. The estimation of immunoglobulins in 45 patients showed significant deficiency, as compared with controls, not only of IgG but also of IgM, and there was an insignificant trend for IgA to be low too. This suggests that the abnormally rapid catabolism of immunoglobulin, previously reported, is not specific for IgG.

Adolescent↗
PubMed1987

Pulmonary abnormalities in obligate heterozygotes for cystic fibrosis.

Parents of children with cystic fibrosis have been reported to have a high prevalence of increased airway reactivity, but these studies were done in a select young, healthy, symptomless population. In the present study respiratory symptoms were examined in 315 unselected parents of children with cystic fibrosis and 162 parents of children with congenital heart disease (controls). The cardinal symptom of airway reactivity, wheezing, was somewhat more prevalent in cystic fibrosis parents than in controls, but for most subgroups this increased prevalence did not reach statistical significance. Among those who had never smoked, 38% of obligate heterozygotes for cystic fibrosis but only 25% of the controls reported wheezing (p less than 0.05). The cystic fibrosis parents who had never smoked but reported wheezing had lower FEV1 and FEF25-75, expressed as a percentage of the predicted value, than control parents; and an appreciable portion of the variance in pulmonary function was contributed by the interaction of heterozygosity for cystic fibrosis with wheezing. For cystic fibrosis parents, but not controls, the complaint of wheezing significantly contributed to the prediction of pulmonary function (FEV1 and FEF25-75). In addition, parents of children with cystic fibrosis reported having lung disease before the age of 16 more than twice as frequently as control parents. Other respiratory complaints, including dyspnoea, cough, bronchitis, and hay fever, were as common in controls as in cystic fibrosis heterozygotes. These data are consistent with the hypothesis that heterozygosity for cystic fibrosis is associated with increased airway reactivity and its symptoms, and that the cystic fibrosis heterozygotes who manifest airway reactivity and its symptoms may be at risk for poor pulmonary function.

Adult↗