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Biomedical subjects

B Christensen

Publications and source records attributed to B Christensen.

At least 19 recordsLinked to original sources
PubMed1992

New rapid test for prenatal detection of trisomy 21 (Down's syndrome): preliminary report.

OBJECTIVE: To devise and evaluate a rapid screening method for detecting trisomy 21 (Down's syndrome) in samples of uncultured amniotic fluid cells. DESIGN: Non-radioactive in situ hybridisation with HY128, a 500,000 base pair yeast artificial chromosome probe specific for chromosome 21. Blinded study of 12 karyotypically normal amniotic fluid samples and eight samples trisomic for chromosome 21. SETTING: Cytogenetic and obstetric services at a tertiary referral centre, Copenhagen. MAIN OUTCOME MEASURES: Time necessary to complete the test. Proportion of cell nuclei containing two and three hybridisation signals in karyotypically normal and abnormal amniotic fluid samples. RESULTS: The test could be completed within three to four days after amniocentesis. In the normal samples a mean of 73% (range 61-82%) of the amniotic cell nuclei showed two hybridisation signals and 6% (0-18%) showed three signals. By contrast, among the trisomic samples 29% (19-38%) of the nuclei exhibited two signals and 48% (31-60%) showed three signals. CONCLUSION: The technique clearly distinguished between normal and trisomic samples. Prenatal diagnosis with in situ hybridisation with chromosome specific probes was fast and may make it possible to screen for selected, aneuploidies. However, the technique is still at a preliminary stage and needs further evaluation and refinement.

Amniocentesis↗
PubMed1992

[Non-radioactive in situ hybridization with chromosome-specific probes].

Non-radioactive in situ hybridization (ISH) is a relatively new and sensitive method for analysis of chromosome aberrations. ISH may be performed on metaphase spreads or directly on interphase cells. By means of ISH, the so-called probes are bound to well-defined regions on the chromosomes of a cell. After a visualization process the probes and thus indirectly the chromosome regions may be observed in a microscope. Chromosome-specific probes become bound to chromosomal DNA segments which are specific for certain groups of chromosomes or only for a single chromosome. The chromosome-specific probes may be subdivided into 1) repetitive probes which are bound at or around the centromere, 2) painting probes which are bound to a certain chromosome in its entire extent or to a limited segment of this and 3) locus-specific probes which are bound to a single unique DNA sequence in the genome. ISH with chromosome-specific probes is of great scientific significance for chromosomal localization of genes. It is to be anticipated that this technique may be employed clinically e.g. in prenatal diagnosis and in the diagnosis of cancer and viruses.

Chromosome Aberrations↗
PubMed1992

Comparison of structure and activities of peroxidases from Coprinus cinereus, Coprinus macrorhizus and Arthromyces ramosus.

Initial structural and kinetic data suggested that peroxidases from Coprinus cinereus, Coprinus macrorhizus and Arthromyces ramosus were similar. Therefore they were characterized more fully. The three peroxidases were purified to RZ 2.5 and showed immunochemical identity as well as an identical M(r) of 38,000, pI about 3.5 and similar amino acid compositions. The N-termini were blocked for amino acid sequencing. The peroxidases had similar retention volumes by anion-exchange and gel-filtration chromatography. All peroxidases showed multiple peaks by Concanavalin A-Sepharose chromatography. The Concanavalin A-Sepharose profiles were different and depended furthermore on a fermentation batch. Tryptic peptide maps were very similar except for one peptide. This peptide contained an N-linked glycan composed of varying ratios of glucosamine and mannose for the three peroxidases. Rate constants and their pH dependence were the same for the three peroxidases using guaiacol or iodide as reducing substrates. We conclude that peroxidases from Coprinus cinereus, Coprinus macrorhizus and Arthromyces ramosus are most likely identical in their amino acid sequences, but deviate in glycosylation which, apparently, has no influence on the reaction rates of the enzyme. We suggest, that the Coprinus fungi express one peroxidase only in contrast to the lignin-degrading white-rot Basidiomycetes, which produce multiple peroxidase isozymes.

Amino Acid Sequence↗
PubMed1992

Rapid prenatal diagnosis of trisomy 18 and triploidy in interphase nuclei of uncultured amniocytes by non-radioactive in situ hybridization.

Two biotinylated chromosome-specific DNA probes were used to quantify the number of chromosomes 18 and 1 in uncultured amniocytes. Thirty-three samples of uncultured amniocytes were hybridized with a chromosome 18-specific DNA probe. Uncultured cells from two of the 33 samples were also hybridized with a chromosome 1-specific probe. Thirty of the samples were disomic with respect to chromosome 18; two samples were trisomic with respect to chromosome 18, and one sample was trisomic with respect to chromosomes 1 and 18. The two cases of trisomy 18 and the single case of triploidy were identified on uncultured cells within 48-72 h after amniocentesis. They were found among five samples from pregnant women who had amniocentesis because of an ultrasonographically identified fetal malformation. A trisomic karyotype could be diagnosed with certainty in uncultured amniocytes because the majority of the responding nuclei exhibited three hybridization signals. In normal cells, the majority of nuclei exhibited two signals. In no cases was there discordance between the genotype as predicted by in situ hybridization and that determined by cytogenetic analysis.

Amniotic Fluid↗
PubMed1992

Genetic amniocentesis at 7-14 weeks of gestation.

Genetic amniocentesis performed at 7-14 weeks of gestation was studied in a series of 138 patients of whom 50 wanted termination of pregnancy (less than or equal to 12 weeks). The material for analysis consisted of 132 samples due to two sampling failures and four samples being handled incorrectly. Forty-eight samples (36 per cent) were taken at 7-12 weeks of gestation, mainly transvaginally (36/48: 75 per cent). The success rate of culture and karyotyping increased with the duration of pregnancy, but was only satisfactory from week 11 onwards. The time until harvest was then 14-15 days. The transvaginal approach is easy to perform and was accepted by the women, but we experienced bacterial or fungal overgrowth in 17 per cent of these samples, whereas no infection occurred in the samples taken transabdominally (n = 96). We conclude that genetic amniocentesis is feasible from week 11, but further studies concerning side effects, especially focusing on the procedure-related abortion risk, should be carried out before early amniocentesis is routinely applied.

Abdomen↗
PubMed1992

Children younger than 4 years of age, referred to an audiological department.

This investigation was performed in order to evaluate why and by whom children less than or equal to 4 years of age were referred to the regional audiological department in Copenhagen: and in addition to describe the audiological investigation and the obtained results in relation to the relevance of the referral. One hundred and forty consecutive first time referred children, 92 males and 48 females, at a median age of 28 months, range 2-49, were included. Of them 71.4% were referred from the general practitioners or local ENT doctors, while only 9.3% were examined on the parents' self-request. The parents were the first to raise suspicion of a hearing loss in 60%, which differs significantly from the 32% correctly found in professionals. The rate of false positive suspicion was similar in the two groups. Forty-nine % of the referred children suffered from hearing impairment, predominantly due to otitis media with effusion. Only 9% of the children were able to perform a pure-tone audiogram. A frequency of 2.9% of children with congenital/early acquired hearing loss was found and a delayed identification demonstrated. The investigation shows that the parents are more efficient in their observation of children concerning hearing loss than professionals, and that the prevalence of "true audiological children" is so restricted that the pediatric audiological services should be centralized and form part of the health hearing service offered to the hearing-impaired. In addition was found that the special equipment and expertise needed for audiological evaluation in young children is used fairly relevantly.

Audiology↗
PubMed1992

On criteria for hearing impairment in children.

As objective criteria concerning hearing impairment/disability may be poorly related to the behavioral patterns of children with hearing deficits, the present investigation was performed. A consecutive series of 172 children, who were examined for the first time at the Audiological Department, was subdivided according to age into two groups: one comprising 98 children at an age from 49 to 84 months, the other comprising 74 children greater than 84 months of age. This second group is supposed to complain of hearing problems if present, and thus constitutes a reference group. Using the criterion for hearing impairment: BEHL 0.5-4 kHz greater than 20 dB HL, the data demonstrated that the frequency of correct and false positive suspicion (detection) of a hearing impairment is similar in parents and professionals with an observer sensitivity of 88%. In addition the frequency of suspicion in parents and professionals in relation to degree of hearing loss corresponds to the frequency of hearing problems, as experienced in the reference group of older children. A certain discrepancy exists between the applied criterion of BEHL 0.5-4 kHz greater than 20 dB and the hearing level resulting in deviating behavioral pattern or experienced hearing deficit in children. This may be ascribed to the predominantly conductive hearing loss in the examined sample. It is concluded that additional investigations on criteria for hearing impairment/disability, including also children with sensorineural hearing loss should be undertaken.

Adolescent↗
PubMed1992

Potential language and attentional networks revealed through factor analysis of rCBF data measured with SPECT.

We used changes in regional cerebral blood flow (rCBF) to disclose regions involved in central auditory and language processing in the normal brain. rCBF was quantified with a fast-rotating, single-photon emission computerized tomograph (SPECT) and inhalation of 133Xe. rCBF data were obtained simultaneously from parallel, transverse slices of the brain. The lower slice was positioned to include both Broca's and Wernicke's areas. The upper slice included regions generally regarded by neurobehaviorists as less related to primary auditory or linguistic functions. We presented three types of auditory stimuli to ten healthy, young volunteers: (a) diotically presented Danish speech, (b) dichotic word stimulation, and (c) white noise. Wilcoxon's signed ranks sum test revealed increased rCBF in language-related areas of cortex, viz., Wernicke's area and its right-sided homologous area as well as in Broca's area (left hemisphere), when subjects listened to narrative speech, compared to white noise (baseline). No significant rCBF differences were detected with this test during dichotic stimulation vs. white noise. A more sophisticated statistical method (factor analysis) disclosed patterns of functionally intercorrelated regions. The factor analysis reduced the highly intercorrelated rCBF measures from 28 regions of interest to a set of three independent factors. These factors accounted for 77% of the total variation in rCBF values. These three factors appeared to represent statistical analogues of independent brain networks involved in (I) auditory/linguistic, (II) attentional, and (III) visual imaging activity.

Acoustic Stimulation↗
PubMed1992

Extended normative data for the Logical Memory subtests of the Wechsler Memory Scale--Revised: responses from a sample of cognitively intact elderly medical patients.

66 cognitively intact geriatric medical patients (ages 70 to 99; M = 77 yr.) were given the Logical Memory subtests of the Wechsler Memory Scale--Revised to extend normative data. 43 women and 23 men, 35 white and 31 black persons made up this urban geriatric sample. A review of patients' medical histories and Mattis' Dementia Rating scores of 129 or greater were used to ensure a sample of cognitively intact patients. Analyses showed that Logical Memory scores were uncorrelated with education, race, sex, or age.

Aged↗
PubMed1992

Homocysteine remethylation during nitrous oxide exposure of cells cultured in media containing various concentrations of folates.

Nitrous oxide irreversibly inactivates cob(I)alamin, which serves as a cofactor of the enzyme methionine synthase catalyzing the remethylation of homocysteine to methionine. In patients exposed to nitrous oxide, increase in plasma homocysteine is a responsive indicator of cob(I)alamin inactivation. In the present work, we measured the inactivation of methionine synthase and the concurrent homocysteine export rate of two murine and four human cell lines during nitrous oxide exposure. When cultured in a standard medium with high content (2.3 microM) of folic acid, the methionine synthase of all cell types was inactivated at an initial rate of 0.05 to 0.14 h-1. The inactivation curves leveled off, and a residual activity of 15 to 45% was observed after 48 h of nitrous oxide exposure. The rate and extent of the nitrous oxide-induced inactivation were markedly reduced when the cells were transferred and cultured (greater than 10 days) in a medium containing low concentration (10 nM) of 5-methyltetrahydrofolate. The methionine synthase inactivation increased in a dose-dependent manner when the 5-methyltetrahydrofolate content of the medium was increased from 3 nM to 2.3 microM. The inactivation of methionine synthase was associated with a marked enhancement of homocysteine export rate of murine fibroblasts and a moderate increase in export from two human glioma cell lines. In contrast, in three leukemic cell lines (murine T-lymphoma R 1.1 cells, human promyelocytic leukemia HL-60 cells and human acute myelogenous leukemia KG-1a cells), the homocysteine export rates were not increased during nitrous oxide exposure. In the responsive murine fibroblasts and the glioma cells, the homocysteine export rate varied inversely to the changes in methionine synthase activity induced by nitrous oxide exposure at different concentrations of folate in the medium. The enhancement of homocysteine export rate of some cell types during nitrous oxide exposure probably reflects inhibition of homocysteine remethylation in intact cells, and highlights the utility of extracellular homocysteine as an indicator of metabolic flux through the methionine synthase pathway. No enhancement of homocysteine export despite inactivation of methionine synthase in three leukemic cell lines questions the functional state of the enzyme in these cells.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed1992

Different patterns of X inactivation in MZ twins discordant for red-green color-vision deficiency.

Two female identical twins who were clinically normal were obligatory heterozygotes for X-linked deuteranomaly associated with a green-red fusion gene derived from their deuteranomalous father. On anomaloscopy, one of the twins was phenotypically deuteranomalous while the other had normal color vision. The color vision-defective twin had two sons with normal color vision and one deuteranomalous son. X-inactivation analysis was done with the highly informative probe M27 beta. This probe detects a locus (DXS255) which contains a VNTR and which is somewhat differentially methylated on the active and inactive X chromosomes. In skin cells of the color vision-defective twin, almost all paternal X chromosomes with the abnormal color-vision genes were active, thereby explaining her color-vision defect. In contrast, a different pattern was observed in skin cells from the woman with normal color vision; her maternal X chromosome was mostly active. However, in blood lymphocytes, both twins showed identical patterns with mixtures of inactivated maternal and paternal X chromosomes. Deuteranomaly in one of the twins is explained by extremely skewed X inactivation, as shown in skin cells. Failure to find this skewed pattern in blood cells is explained by the sharing of fetal circulation and exchange of hematopoietic precursor cells between twins. These data give evidence for X inactivation of the color-vision locus and add another MZ twin pair with markedly different X-inactivation patterns for X-linked traits.

Chromosome Mapping↗
PubMed1991

A nonradioactive assay for N5-methyltetrahydrofolate-homocysteine methyltransferase (methionine synthase) based on o-phthaldialdehyde derivatization of methionine and fluorescence detection.

The enzyme N5-methyltetrahydrofolate-homocysteine methyltransferase (methionine synthase, EC 2.1.1.13) catalyzes the conversion of homocysteine to methionine in the presence of a reducing system. N5-Methyltetrahydrofolate serves as a methyl donor in this reaction. An assay for the enzyme is described, which is based on methionine quantitation by o-phthaldialdehyde (OPA) derivatization and reversed-phase liquid chromatography. The enzymatic reaction is linear for at least 120 min under reducing conditions (125 mM 2-mercaptoethanol) and running the assay below an oil layer. This reducing system does not interfere with formation of the methionine-OPA adduct, which is separated from interfering compounds and an internal standard (norvaline) by a mobile phase adjusted to pH 5.0. The inclusion of internal standard increases the precision of the assay and corrects for the variable fluorescence yield due to occasional inaccurate pH adjustment before the derivatization step. Norvaline was suitable for this purpose because it elutes close to methionine and is not a natural amino acid present in biological extracts. This nonradioactive assay for methionine synthase was evaluated by comparison with a conventional method based on isolation of radioactive methionine by anion-exchange chromatography and by determination of enzyme activity in extract from cultured cells and liver.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed1991

[A centrifugal pump used as a support of left ventricular pumping function after extracorporeal circulation].

The first Danish employment of a centrifugal pump for relief of the left ventricle after open heart surgery is presented. A man aged 72 years with three-vessel coronary arteriosclerosis was submitted to a coronary by-pass operation. At the conclusion of the operation, the pumping capacity of the heart was found to be so reduced that it was not possible to maintain an adequate minute-volume without support from a mechanical pump. The circulation in this patient was supported for four hours by means of an outflow catheter from the left atrium and an inflow catheter in the ascending aorta. After this, the patient's own heart could achieve the necessary minute-volume. The remainder of the postoperative course was uncomplicated.

Aged↗
PubMed1991

Homocysteine export from cells cultured in the presence of physiological or superfluous levels of methionine: methionine loading of non-transformed, transformed, proliferating, and quiescent cells in culture.

Determination of the transient increase in plasma homocysteine following administration of excess methionine is an established procedure for the diagnosis of defects in homocysteine metabolism in patients. This so-called methionine loading test has been used for 25 years, but the knowledge of the response of various cell types to excess methionine is limited. In the present paper we investigated homocysteine export from various cell types cultured in the presence of increasing concentrations (15-1,000 microM) of methionine. For comparison of homocysteine export, the export rates per million cells were plotted versus cell density for proliferating cells, and versus time for quiescent cells. The homocysteine export from growing cells was greatest during early to mid-exponential growth phase, and then decreased as a function of cell density. The export rate was higher from phytohemagglutinin-stimulated than non-stimulated lymphocytes, and higher from proliferating than from quiescent fibroblasts. The hepatocytes showed highest export rate among the cell types investigated. The enhancement of homocysteine export by excess methionine ranged from no stimulation to marked enhancement, depending on cell type investigated, and three different response patterns could be distinguished: 1) quiescent fibroblasts and growing murine lymphoma cell showed no significant increase in homocysteine export following methionine loading; export from human lymphocytes was only slightly enhanced in the presence of excess methionine; 2) the homocysteine export from proliferating hepatoma cells and benign and transformed fibroblasts was stimulated three to eightfold by increasing the methionine concentration in the medium from 15 to 1,000 microM; and 3) the response to methionine loading was particularly increased (about 15-fold) in non-transformed primary hepatocytes in stationary culture. The results outline a potentially useful procedure for the comparison of homocysteine export during cell growth in the presence of various concentrations of methionine. The results are discussed in relation to the special feature of homocysteine metabolism in various cell types and tissues including liver, and to the possible source of plasma homocysteine following methionine loading in vivo.

Animals↗
PubMed1991

The use and benefit of in-the-ear hearing aids. A four-year follow-up examination.

The present investigation was performed in order to evaluate the use and benefit of in-the-ear hearing aids (ITE-HAs) after a 4-year observation period, and to examine the validity of this type of hearing aid. A sample of 537 subjects still in possession of ITE-HAs, fitted in 1985, responded to a postal questionnaire in 1989, including questions identical to the first follow-up in 1985. The 537 persons correspond to 60% of the originally fitted sample of 894 subjects. The investigation indicated that no change in the use of or benefit from ITE-HAs has taken place during a 4-year period, and in addition the manipulative skills of the hearing aid users did not improve. However, the overall frequency of handling problems is low, though with a tendency to increase in the age group above 75 years. It is concluded that the use of and benefit obtained with ITE-HAs remains unchanged over a 4-year period; that the use and benefit is similar in the age groups below and above 75 years of age; that the ITE-HAs seem to be fairly stable during a 4-year period.

Adult↗