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Biomedical subjects

J Cohen

Publications and source records attributed to J Cohen.

At least 379 records · Page 21Linked to original sources
PubMed1998

Spontaneous abortions are reduced after preconception diagnosis of translocations.

PURPOSE: Preimplantation genetic diagnosis of translocations has seldom been attempted. Recently, a genetic test based on analyzing polar bodies at the methaphase stage, following fluorescent in situ hybridization with commercially available whole-chromosome painting DNA probes has been presented. Here we report the use of this method in seven couples in whom the female was a carrier of one of these balanced translocations: 45,XX,der (13q;14q)(q10;q10) (two cases), 46,XX,t(4;14)(p15.3;q24), 45,XX,der(14q;21q) (q10;q10), 46,XX,t(7;20)(q22;q11.2), 46,XX,t(9,11)(p24;q12), 46,XX,t(14;18)(q22;q11), and 46,XX,t(3;8)(q11;q11). METHODS: The original method was improved in two ways. First, centromeric probes for one or both chromosomes involved in the translocation were added to avoid misdiagnosis caused by possible confusion of first polar body monovalent chromosomes (with two chromatids each) with single chromatids. Second, for cases with terminal translocations where commercially available probes do not cover telomere sequences, a telomere probe labeling the translocated fragment was added. RESULTS: A total of 26 abnormal, 18 balanced, and 22 normal eggs was detected. Nine normal and seven balanced embryos were transferred, resulting in eight (50%) implanting, of which one spontaneously aborted. To date, the remainder have produced karyotypically normal or balanced babies and ongoing pregnancies. The rate of spontaneous abortions after preimplantation genetic diagnosis (12.5%) was significantly reduced (P < 0.001) compared to natural cycles in the same patients (95%). CONCLUSIONS: With the above improvements, the test can characterize any translocation of maternal origin and produce a high pregnancy rate and an apparently low frequency of spontaneous abortion.

Abortion, Spontaneous↗
PubMed1998

Statistically robust approaches for sib-pair linkage analysis.

Many traits that distinguish one individual from another, such as height or weight, are clearly heritable and yet vary continuously in populations. Continuous, heritable variation in trait levels presumably reflects the segregation of multiple genes, but elucidation of the genetic architecture of quantitative traits has been limited. Haseman & Elston (1972) developed a genetically robust method (HE) for detecting linkage to quantitative trait loci using sib-pairs. The method is based on a simple linear regression of the squared sib-pairs trait difference on the proportion of alleles shared identical by descent at a marker locus. Linkage is detected by a negative slope which has been traditionally assessed by a standard t-test. Wan, Cohen & Guerra (1997) have shown that the standard t-test is robust to the violations of the stochastic assumptions underlying the test. In practice, however, the standard t-test, based on least-squares regression, is sensitive to outliers. The presence of outliers in the data can lead to false positive and false negative linkage results. Accordingly we have developed and evaluated a statistically robust procedure for the HE approach to linkage. The procedure is based on robust regression. Simulation studies show that this robust procedure has greater power than the standard t-test in the presence of outliers, and has similar power to the standard t-test in the absence of outliers. This robust procedure also shows greater power than rank-based approaches either in the absence or presence of outliers. To illustrate the methods using real data we reanalyse data from two lipoprotein systems that motivated this work.

Adult↗
PubMed1998

Genetic linkage analysis using lognormal variance components.

Typically genetic studies of continuous traits such as cholesterol levels or blood pressure assume that interindividual variability follows a normal distribution. Here we develop methods to analyze positively skewed data by assuming a lognormal distribution. We develop a variance components approach for identifying such effects from a major gene, residual polygenic factors and nongenetic factors. We compare by a simulation study results from fitting this lognormal model with either applying the log transformation or not transforming the data. We found that the lognormal model provided more precise estimates and more powerful tests than a simple log transformation when analyzing lognormally distributed data. Power varied with sibship size. For the same total number of nonindependent sibpairs, larger sibships were less powerful. However, larger sibships are more economical because they require a smaller sample size to obtain a specified power. To illustrate the application of this lognormal model to real data, we studied evidence for linkage between triglycerides and the lipoprotein lipase gene.

Genetic Linkage↗
PubMed1998

Systemic cytokine response to hepatic resections under total vascular exclusion.

OBJECTIVE: To investigate the systemic cytokine response to major liver surgery as the basis for assessing potential new treatments. DESIGN: Open prospective study. SETTING: University hospital, UK. SUBJECTS: Thirteen patients undergoing elective hepatic resections that involved total vascular exclusion of the liver. INTERVENTIONS: Blood samples were taken preoperatively, during the operation, and during the first four postoperative days. Concentrations of endotoxin, interferon gamma (IFN-gamma), tumour necrosis factor alpha (TNFalpha), interleukin-1 (IL-1), and interleukin-6 (IL-6) were measured. RESULTS: Endotoxin concentrations were raised in 3/13 patients before operation and in 6 patients during the postoperative period. TNFalpha concentrations were undetectable. IFN-gamma and IL-1 responses followed a low and inconclusive pattern. IL-6 was significantly increased from 6 hours after operation to the third postoperative day, peaking at 699 (+/-277) pg/ml at 24 hours (p < 0.01). The two patients who died had the highest postoperative concentrations of IL-6. CONCLUSIONS: There is a pronounced systemic response to hepatic resection under total vascular exclusion that is reflected by the increase in IL-6 concentration and correlates with the operative blood loss and postoperative outcome. This might be used as an indicator of the response to specific treatments in this type of surgery. Treatments that minimise the IL-6 response to major hepatic resection may be of value.

APACHE↗
PubMed1998

Long-term efficacy and immune responses following immunization with the RTS,S malaria vaccine.

The malaria sporozoite vaccine candidate RTS,S, formulated with an oil-in-water emulsion plus the immunostimulants monophosphoryl lipid A and the saponin derivative QS21 (vaccine 3), recently showed superior efficacy over two other experimental formulations. Immunized volunteers were followed to determine the duration of protective immune responses. Antibody levels decreased to between one-third and one-half of peak values 6 months after the last dose of vaccine. T cell proliferation and interferon-gamma production in vitro were observed in response to RTS,S or hepatitis B surface antigen. Seven previously protected volunteers received sporozoite challenge, and 2 remained protected (1/1 for vaccine 1, 0/1 for vaccine 2, and 1/5 for vaccine 3). The prepatent period was 10.8 days for the control group and 13.2 days for the vaccinees (P < .01). Immune responses did not correlate with protection. Further optimization in vaccine composition and/or immunization schedule will be required to induce longer-lasting protective immunity.

Adolescent↗
PubMed1998

Intracellular pH regulation in the human oocyte.

We have used fluorescence techniques to study the regulation of intracellular pH during fertilization and preimplantation embryo development in human oocytes. The intracellular pH of human oocytes during maturation and fertilization was always 7.4, suggesting that these processes do not involve long-term changes in intracellular pH. The recovery of intracellular pH of human oocytes and embryos after extracellular acid or alkaline shock was investigated. Fresh metaphase II oocytes and preimplantation embryos showed similar rates of recovery following alkaline shock. However, aged and immature oocytes had a significantly slower rate of recovery to physiological pH. Early embryos up to the morula stage were unable to recover following acidosis, whereas blastocysts could control both acidosis and alkalosis. We assessed the sensitivity of fertilization and early development in the human to extracellular pH. Our results show that insemination in the human is pH-sensitive, whereas intracytoplasmic injection (ICSI) activated oocytes at all pH tested. We suggest that this is due to the pH-sensitivity of the sperm-zona pellucida interaction, which is bypassed during the ICSI procedure. Further development in human embryos is more sensitive to alkalinity than acidity. We discuss these results in terms of the extracellular pH in vivo in the female reproductive tract.

Blastocyst↗
PubMed1998

Culture and quality control of embryos.

Improvement of embryo quality during in-vitro culture can be achieved by understanding and controlling the requirements of gametes and embryos. The most obvious route is to alter culture media, but standardization could be influenced by diverse environmental factors. Abnormal embryos from patients with multiple failures probably do not benefit from standardization and require specialized therapy, that is if their physiology is not already irreversibly jeopardized during gametogenesis. This paper describes the adverse environmental factors present in laboratory air and released by common products used by laboratories. Assays and results of the air determinations in several laboratories are reported, as well as potential counter measures. The possibility of altering the immediate environment of the nucleus of the egg by ooplasmic transplantation is also considered, and the first attempts resulting in two ongoing pregnancies are reported.

Culture Techniques↗
PubMed1998

Genetic regulation of egg and embryo survival.

In both mice and humans, 15-50% of embryos die during the preimplantation period from mechanisms that are largely unknown. Two major criteria predict preimplantation embryo quality, the rate of development and the degree of fragmentation. We review evidence that both of these criteria have a genetic basis. Rate of development and subsequent embryo survival are controlled by a gene, Ped, we discovered in the mouse. Although progress is being made in the search for the human homologue of the mouse Ped gene, it has not yet been identified. Fragmentation, observed in both mouse and human embryos, is probably the result of apoptosis. We analysed transcription of two genes that regulate apoptosis, bcl-2 and bax, and found that both are transcribed in mouse and human preimplantation embryos. Overall, the literature reviewed and new data presented in this paper support the concept that there is a genetic basis for preimplantation egg and embryo survival.

Animals↗
PubMed1998

How to avoid multiple pregnancies in assisted reproduction.

The international rates of triplet or higher order pregnancies after assisted reproduction are 7.3% at conception, 6.5% before reduction and 3.85% at birth. The obstetric and neonatal outcomes for twins and triplets show that reducing the proportion of multiple pregnancies should be a goal for centres undertaking in-vitro fertilization (IVF) and embryo transfer.

Adult↗
PubMed1998

Cryopreservation of activated mouse oocytes and zygote reconstitution after thaw.

A new approach to cryopreservation of unfertilized oocytes is proposed using techniques of artificial egg activation combined with nuclear transplantation. Matured mouse oocytes were released from metaphase II arrest by brief exposure to alcohol, allowed to progress to the pronuclear stage and then frozen according to a standard freezing protocol in propandiol. After thaw the female pronuclei were enucleated and fused with a male karyoplasts that were divided from in-vivo fertilized zygotes. Reconstituted zygotes, fresh and cryopreserved culture control zygotes were cultured to the blastocyst stage and transferred to pseudopregnant recipients. The rate of blastocyst formation was 75.8, 91.6 and 44.1% respectively. A total of 110, 215 and 70 blastocysts were transferred to pseudopregnant females respectively. The implantation rates were 36.4, 72.0 and 75.7% while the rates of fetal viability at mid-gestation were 15.5 (P < 0.0001), 51.1 and 37.1% respectively.

Animals↗
PubMed1998

The origin, effects and control of air pollution in laboratories used for human embryo culture.

Testing shows that most laboratories conducting human gamete and embryo culture have air quality and sources of contamination that exceed the levels measured in homes, businesses and schools. The sources of these contaminants have been shown to be either from activities outside the laboratory, or emitted from materials used in the facility, such as compressed gas, cleaning and sterilizing agents, plastic and stored materials. Both the laboratory structure and the air handling systems may affect the air composition. The significance of these findings is being validated by the accumulation of field case studies and now by assay procedures. Products given off by road sealant were shown to have accumulated in one of the examined laboratories, adjacent to a large re-surfaced parking area. Aldehydes such as acrolein, hexanal, decanal, pentanal and others were detected at elevated concentrations that were statistically significant. Since it is not appropriate to add potentially suspect chemicals to human embryos, we used a mouse-model to study the effect of acrolein. The growth of mouse embryos was significantly affected after acrolein was added at different concentrations to the culture environment. The physiological effect was noted at concentrations in the low ppm range. The testing end-point of embryo death must still be considered to be a crude basis for evaluating toxicological effects, since it involves addition of compounds to culture media and unprotected growth until the blastocyst stage. The findings may, however, support observations of decreased pregnancy rate following exposure of human embryos to aldehydes or other adverse conditions. With proper engineering and material selection, it is possible to reduce such contamination. The usefulness of this approach for controlling aldehydes has been demonstrated by decreasing levels in the laboratory to below those of the outside air.

Acrolein↗
PubMed1998

The application of co-culture in assisted reproduction: 10 years of experience with human embryos.

Co-culture techniques using fetal bovine uterine fibroblasts or bovine oviductal epithelial cells have improved embryonic development prior to replacement in humans. In initial co-culture trials, embryo development and implantation rates increased after just 1 day in culture. The most overt characteristics noted following co-culture were improved blastomere development and characteristics, reduced fragmentation, and the appearance of swollen blastomeres. In addition, an increase in the incidence of zona thickness variation was detected. Improved development of polyspermic and supernumerary embryos to the blastocyst stage was noted in initial trials. Retrospective analysis indicated that certain patient subgroups benefit the most from co-culture. As a result, co-culture is now applied routinely to patients that have previously failed attempts at in-vitro fertilization (IVF) and/or have endocrine imbalances such as polycystic ovarian syndrome and elevated day 3 concentrations of follicle stimulating hormone (FSH). The use of co-culture prior to or following cryopreservation has also proven to be beneficial to human embryos. The proposed beneficial mechanisms thought to improve embryonic development include a secretory and/or a scavenging role. Evidence describing the postulated benefits is discussed.

Coculture Techniques↗
PubMed1998

The first births and ongoing pregnancies associated with sperm cryopreservation within evacuated egg zonae.

This new procedure principally aims to avoid a second or possibly multiple surgical procedures for sperm extraction from the male partner in cases of limited amounts of sperm cells, where normal freeze-thaw protocols would fail. Patients (n = 34) diagnosed as azoospermic, extreme oligozoospermic, or oligoasthenozoospermic underwent the process of sperm cryopreservation within evacuated egg zonae. Other samples were allocated to conventional sperm freezing. Sperm samples were acquired using testicular sperm extraction (TESE), microepididymal sperm aspiration (MESA), or fresh ejaculate. Subsequently, five of these 34 couples have undergone in-vitro fertilization (IVF) and achieved normal fertilization using post-thawed spermatozoa frozen under zonae pellucidae in conjunction with intracytoplasmic sperm injection (ICSI). The average fertilization rate for the post-thaw injected spermatozoa was 65%. This is comparable with the regular fertilization rate of 65% for combined MESA and TESE using fresh spermatozoa. All patients underwent embryo transfer. The average implantation rate per embryo was 31%; nearly the same for regular MESA/TESE ICSI cycles (32%). The first pregnancy associated with this procedure concluded with the full term delivery of healthy twin girls on July 18, 1997. The remaining four thaw procedures resulted in another twin delivery, an ongoing singleton gestation, a negative pregnancy test and a biochemical pregnancy respectively.

Adult↗
PubMed1998

Ooplasmic transfer in mature human oocytes.

Ooplasmic transplantation aimed at restoring normal growth in developmentally compromised oocytes and embryos was evaluated in seven couples (eight cycles) with multiple implantation failures. Two approaches were investigated to transfer ooplasm from donor eggs at metaphase II (MII) stage into patient MII eggs: (i) electrofusion of a ooplasmic donor fragment into each patient egg (three cycles), and (ii) direct injection of a small amount of ooplasm from a donor egg into each patient egg (five cycles). Some donor eggs were used multiple times. Donor eggs were divided into two groups, one being used for ooplasmic extraction and the other one for egg donation. Cleaved embryos resulting from the latter were cryopreserved, where numbers and satisfactory development permitted. A second control group consisted of embryos derived from patient eggs after intracytoplasmic sperm injection without ooplasmic transfer. This was performed when sufficient number of eggs were available (n = 5). Donor eggs (n = 40) were evaluated cytogenetically after micromanipulation in order to confirm the presence of chromosomes. One egg was anuclear and the recipient embryos were not transferred. Normal fertilization was significantly higher after injection of ooplasm (63%) in comparison with fusion (23%). Pronuclear anomalies appeared enhanced after fusion with ooplasts. Embryo morphology was not improved in the three cycles with electrofusion and patients did not become pregnant. An improvement in embryo morphology was noted in two patients after injection of ooplasm and both became pregnant, but one miscarried. A third pregnancy was established in the repeat patient, without obvious embryo improvement. One baby was born and the third pregnancy is ongoing with a normal karyotype. Two other patients with male factor infertility had poor embryos after ooplasmic injection, but the donor embryo controls were also poor. The patients did not become pregnant and had no donor embryos frozen. Ooplasmic transfer at the MII stage may be promising in patients with compromised embryos; however, evaluation of ooplasmic anomalies and optimization of techniques will require further investigation prior to widescale application.

Cell Culture Techniques↗
PubMed1998

Mitochondrial DNA deletion in human oocytes and embryos.

Mitochondrial DNA (mtDNA) deletions are present in both human oocytes and embryos. It has been found that these tissues contain a mtDNA mutation which is present in high amounts in patients with Kearns-Sayre syndrome (KSS) and progressive external ophthalmoplegia. In the present study, the frequency of this KSS deletion was investigated in human oocytes and embryos. Using a nested primer polymerase chain chian reaction (PCR) strategy, the frequency of the KSS deletion in 74 human oocytes and 137 embryos was found to be 32.8 and 8.0% respectively. Using a 'long PCR-short PCR' nested primer strategy, the frequency of the KSS deletion in 181 human oocytes and 104 embryos was found to be 47.0 and 20.2% respectively. There was no statistical correlation between the age of the patients at the time of oocyte retrieval and the presence of the deleted molecules. There was a statistical difference between the presence of the deleted molecules in oocytes versus embryos using either technique (P < 0.0001). The relevance of these findings to the accumulation of low levels of deleted mtDNA in both oocytes and embryos is discussed in this study.

Adult↗