Methylation-specific multiplex ligation-dependent probe amplification: utility for prenatal diagnosis of parental origin in human triploidy.

OBJECTIVE: When a triploid pregnancy is diagnosed prenatally, gynaecologists have traditionally relied on the histopathological examination of the tissue from the terminated pregnancy to determine if the pregnancy is molar. However, reproducibility is poor and variability is high when diagnosing hydatidiform moles. Triploid pregnancies can have either the chromosomal constitution of two maternal and one paternal set, or two paternal and one maternal set, but only the conceptuses with two paternal sets have the potential to cause maternal complications. Therefore, it would be beneficial to introduce a method that gives the gynaecologist the parental origin of the genome of the triploid conceptus as early as possible, without delaying the process by first collecting parental samples. METHODS: Using methylation-specific multiplex ligation-dependent probe amplification, we measured methylation levels at different imprinted sites. RESULTS: We were able to correctly determine the parental origin of the genome in all 105 triploid pregnancies analysed. CONCLUSIONS: We present methylation-specific multiplex ligation-dependent probe amplification as a method capable of determining the parental origin of the genome of triploid conceptuses within 24 h; it is inexpensive, simple and easy to use, and parental samples are not needed.

Breast cancer after bilateral risk-reducing mastectomy.

This study aims to evaluate the incidence of breast cancer after risk-reducing mastectomy (RRM) in healthy BRCA mutation carriers. This study is a long-term follow-up of 307 BRCA mutation carriers of whom 96 chose RRM. None of the study participants had a previous history of breast or ovarian cancer nor had they undergone RRM or risk-reducing bilateral salpingo-oophorectomy (BSO) prior to the time of BRCA testing. The annual incidence of post-mastectomy breast cancer was 0.8% compared with 1.7% in the non-operated group. Implications of these findings in relation to genetic counseling and future management are discussed.

Anti-inflammatory heat shock protein 70 genes are positively associated with human survival.

A positive relationship between stress tolerance and longevity has been observed in several model systems. That the same correlation is applicable in humans and that it may be open to experimental manipulation for extending human lifespan requires studies on association of stress genes with longevity. The involvement of heat shock protein 70 (Hsp70) in cellular maintenance and repair mechanisms, including its role as an anti-inflammatory protein, makes it a suitable candidate for studying such associations. We have studied the association of three single nucleotide polymorphisms, HSPA1A (-110A>C), HSPA1B (1267A>G), and HSPA1L (2437T>C), present in the three HSP70 genes, with human survival, in a cohort of individuals born in the year 1905. This population cohort is a part of the longitudinal study of Danish nonagenarians. Since DNA samples were already collected in 1998, this gave us the opportunity to perform survival analysis on these subjects. Haplotype relative risk, and genotype relative risk were calculated to measure the effects of haplotypes and genotypes on human survival in a sex-specific manner. A significant association of HSPA1A-AA (RR=3.864; p=0.016) and HSPA1B-AA (RR=2.764; p=0.039) genotypes with poor survival was observed in female subjects. Also the female carriers of haplotype G-C-T had longer survival than the non-carriers (HRR=0.550; p=0.015). On an average, female carriers of the G-C-T haplotype live about one year longer than non-carriers. This result corroborates our previous observations from heat shock response (HSR) study where we had shown that after heat stimulation, mononuclear cells from the carriers of genotype HSPA1L-TT had better HSR than cells with the HSPA1L-CC genotype.

Risk-reducing mastectomy and salpingo-oophorectomy in unaffected BRCA mutation carriers: uptake and timing.

Once female carriers of a BRCA mutation are identified they have to make decisions on risk management. The aim of this study is to outline the uptake of risk-reducing surgery in the Danish population of BRCA mutation positive women and to search for factors affecting this decision. We analysed data from 306 healthy BRCA carriers with no personal history of ovarian or breast cancer. We found a 10-year uptake of 75% for risk-reducing salpingo-oophorectomy and 50% for risk-reducing mastectomy by time to event analysis. Age and childbirth influenced this decision. The uptake rate has not changed significantly over the last decade. Risk-reducing surgeries are widely acceptable among Danish BRCA mutation positive women and the uptake of prophylactic mastectomy is higher than in most other countries.

Nuclei size in relation to nuclear status and aneuploidy rate for 13 chromosomes in donated four cells embryos.

PURPOSE: The aim was to elucidate if the nuclear size and number are indicative of aberrant chromosome content in human blastomeres and embryos. METHODS: The number of nuclei and the nucleus and blastomere size were measured by a computer controlled system for multilevel analysis. Then the nuclei were enumerated for 13 chromosomes by a combination of PNA and DNA probes. RESULTS: In the mononucleated embryos there was no difference in the mean size of chromosomally normal and abnormal nuclei but a significant difference in the mean nuclei size of nuclei that had gained chromosomes compared to nuclei that had lost chromosomes. The nuclei from multinucleated blastomeres had a significant smaller mean size and the frequency of chromosomally aberrant blastomeres was significantly higher. CONCLUSION: The mean nuclear size is not a marker for the chromosome content in mononucleated embryos. However, it seems that the nuclei size can be related to multinucleation and maybe to the chromosome content.

Strategy in clinical practice for classification of unselected colorectal tumours based on mismatch repair deficiency.

OBJECTIVE: Deficiency of DNA mismatch repair (MMR) causes microsatellite instability (MSI) in a subset of colorectal cancers. Patients with these tumours have a better prognosis and may have an altered response to chemotherapy. Some of the tumours are caused by hereditary mutations (hereditary nonpolyposis colon cancer or Lynch syndrome), but most are epigenetic changes of sporadic origin. The aim of this study was to define a robust and inexpensive strategy for such classification in clinical practice. METHOD: Tumours and blood samples from 262 successive patients with colorectal adenocarcinomas were collected. Expression of the MMR proteins MLH1, MSH2, and MSH6 by immunohistochemistry (IHC) was compared with MSI DNA analysis. Methylation analysis of MLH1 and mutation analysis for BRAF V600E were compared in samples with MSI and/or lack of MLH1 expression to determine if the tumour was likely to be sporadic. RESULTS: Thirty-nine (14.9%) of the tumours showed MMR deficiency by IHC or by microsatellite analysis. Sporadic inactivation by methylation of MLH1 promoter was found in 35 patients whereby the BRAF activating V600E mutation, indicating sporadic origin, was found in 32 tumours. On the basis of molecular characteristics we found 223 patients with intact MMR, 35 patients with sporadic MMR deficiency, and four patients who were likely to have hereditary MMR deficiency. CONCLUSION: To obtain the maximal benefit for patients and clinicians, MMR testing should be supplemented with MLH1 methylation or BRAF mutation analysis to distinguish sporadic patients from likely hereditary ones. MMR deficient patients with sporadic disease can be reassured of the better prognosis and the likely hereditary cases should receive genetic counselling.

Osteoclast nuclei of myeloma patients show chromosome translocations specific for the myeloma cell clone: a new type of cancer-host partnership?

A major clinical manifestation of bone cancers is bone destruction. It is widely accepted that this destruction is not caused by the malignant cells themselves, but by osteoclasts, multinucleated cells of monocytic origin that are considered to be the only cells able to degrade bone. The present study demonstrates that bone-resorbing osteoclasts from myeloma patients contain nuclei with translocated chromosomes of myeloma B-cell clone origin, in addition to nuclei without these translocations, by using combined FISH and immunohistochemistry on bone sections. These nuclei of malignant origin are transcriptionally active and appear fully integrated amongst the other nuclei. The contribution of malignant nuclei to the osteoclast population analysed in this study was greater than 30%. Osteoclast-myeloma clone hybrids contained more nuclei than normal osteoclasts and their occurrence correlated with the proximity of myeloma cells. Similar hybrid cells were generated in myeloma cell-osteoclast co-cultures, as revealed by tracing myeloma nuclei using translocations, bromo-deoxyuridine, or the Y chromosome of male myeloma cells in female osteoclasts. These observations indicate that hybrid cells can originate through fusion between myeloma cells and osteoclasts. In conclusion, malignant cells contribute significantly to the formation of bone-resorbing osteoclasts in multiple myeloma. Osteoclast-myeloma clone hybrids reflect a previously unrecognized mechanism of bone destruction in which malignant cells participate directly. The possibility that malignant cells corrupt host cells by the transfer of malignant DNA may have been underestimated to date in cancer research.

The pattern of chromosome-specific variations in telomere length in humans shows signs of heritability and is maintained through life.

This paper characterizes the distribution of telomere length on individual chromosome arms in humans. By fluorescent in situ hybridization (FISH), followed by computer-assisted analysis of digital images, it is shown that the distribution of telomere length on individual chromosome arms is not random, but that humans have a common telomere profile. This profile exists in lymphocytes, amniocytes and fibroblasts, and seems to be conserved during life. A closer look at the overall pattern of the profile shows that the length of the telomeres in general follows the total chromosome length. In addition to the common profile, it is found that each person has specific characteristics, which are also conserved throughout life. Studying both twins and families we have obtained indications that these individual characteristics are at least partly inherited. Altogether, our results suggest that the length of individual telomeres might occasionally play a role in the heritability of life span.

Sequential FISH analysis using competitive displacement of labelled peptide nucleic acid probes for eight chromosomes in human blastomeres.

BACKGROUND: The aim was to introduce a new strategy based on peptide nucleic acid (PNA) probes and competitive displacement for using fluorescence in-situ hybridization (FISH) analysis on human blastomeres. METHODS: Sequential FISH analysis with PNA probes and competitive displacement was performed using three different probe sets. The first set consisted of labelled probe only. The second and third sets included labelled as well as unlabelled probe, corresponding to the labelled probes in the previous cycles. The probes for enumeration were for chromosome 1, 13, 16, 17, 18, 21, X and Y. RESULTS: The performance of PNA probes was similar to the established DNA probes. The strategy of competitive displacement resulted in a destabilization of already bound probe before the next FISH cycle at only 50 degrees C, which allowed for up to five sequential FISH cycles without loss of signal. CONCLUSIONS: PNA probes are a good alternative to DNA probes in the present set-up, since the low temperature required both for binding and destabilization of PNA probes minimizes the loss of signal, and several FISH cycles can therefore be carried out before FISH errors occur.

Studies on the isolation and identification of fetal nucleated red blood cells in the circulation of pregnant women before and after chorion villus sampling.

OBJECTIVE: To investigate the feasibility of various molecular forms of hemoglobin as markers for fetal nucleated red blood cells (NRBCs). METHODS: The presence of epsilon and gamma globin positive NRBCs was investigated in pure fetal blood and in blood from pregnant women before and after chorion biopsy. Maternal samples were enriched for NRBCs by various conventional methods, including limited enrichment by only positive CD71 selection or single density gradient. We searched for fetal cells on slides by automated scanning. Fetal cells were defined by (1) the presence of epsilon or gamma globin and (2) simultaneously by the presence of a Y chromosome signal. RESULTS: 18 of 25 gamma globin positive cells identified in blood samples after chorion biopsy were chromosome Y signal positive, and 1 cell had two X chromosome signals. 263 of 339 epsilon globin positive cells identified in blood samples after chorion biopsy were hybridized with X and Y chromosome probes. None had two X signals, and 249 were Y positive. In blood samples before chorion biopsy, only 1 epsilon globin positive fetal NRBC and no epsilon globin positive maternal NRBCs were found. CONCLUSIONS: Epsilon globin may be specific for fetal NRBCs. Only 1 epsilon globin positive fetal cell was identified in 1 of 12 blood samples before chorion biopsy, representing a total of 182 ml of maternal blood. This suggests that most fetal cells found in maternal blood by fluorescence in situ hybridization methods may not be NRBCs.

[Preimplantation genetic diagnosis. The first experiences in Denmark]. / Praeimplantations genetisk diagnostik. De første erfaringer i Danmark.

INTRODUCTION: Preimplantation genetic diagnosis (PGD) is a possible alternative to prenatal diagnosis, whereby families with serious inherited diseases can avoid having children with the disease. The genetic diagnosis is performed on embryos before implantation and therefore implies IVF. Hence, PGD offers the possibility of transferring embryos without disease, thereby avoiding termination of pregnancy owing to an affected fetus. MATERIAL AND METHODS: Activities at the Centre for Preimplantation Genetic Diagnosis at Aarhus University Hospital since its opening in February 1999 are described. The fluorescent in situ hybridisation (FISH) technique was used for sex selection (hemophilia A and Duchenne's muscular dystrophy) and translocations. The polymerase chain reaction (PCR) was used for cystic fibrosis. RESULTS: Of 20 PGD cycles started, 15 were successful in terms of transference of healthy or carrier embryos. A positive pregnancy test was found after six of 15 embryo transfers (40%) with two subsequent clinical pregnancies. CONCLUSIONS: The present pregnancy rates with PGD are comparable to those following IVF; the clinical pregnancy rate may seem low, but the cycle numbers are small. Preimplantation genetic diagnosis seems to be a realistic alternative for selected genetic diseases, in cases where the couple find abortion unacceptable.

Multiplex PCR for screening of microdeletions on the Y chromosome.

PURPOSE: The aim of this study was to develop a multiplex PCR protocol, which could be suitable for screening of microdeletions in the three azoospermia factor (AZF) regions on the Y chromosome. METHODS: In the screening protocol, 36 known sequence tagged site (STS) primer pairs were first tested in single PCR reactions and thereafter combined in multiplex PCR to test for specificity and sensitivity in order to develop a stable and reliable multiplex PCR assay to detect Y microdeletions. RESULTS: Of the 36 primers tested, 11 turned out not to be specific or produced PCR products that were too weak, and they were therefore not used in the multiplex PCR. The remaining 25 STSs were selected on the basis of their ability to be reproducibly amplified with each other using identical amplification conditions. Five multiplex sets, each consisting of five primer pairs, were established in the multiplex PCR setup. CONCLUSION: The multiplex PCR protocol presented in this study is an easy and reliable method for detection of Y chromosome microdeletions and could be used for screening of infertile men to allow genetic counseling about the risk of transmitting infertility from father to son.

LDL receptor-GFP fusion proteins: new tools for the characterisation of disease-causing mutations in the LDL receptor gene.

The function of a series of LDL receptor GFP fusion proteins with different, flexible, unstructured spacer regions was analysed. An optimised version of the fusion protein was used to analyse the effect of an LDL receptor mutation (W556S) found in FH patients and characterised as transport defective. In cultured liver cells this mutation was found to inhibit the transport of LDL receptor GFP fusion protein to the cell surface, thus leading to impaired internalisation of fluorescent labelled LDL. Co-localisation studies confirmed the retention of the mutant protein in the endoplasmic reticulum. Wild type (WT) and W556S LDL receptor GFP fusion proteins were expressed in mouse liver by means of hydrodynamic delivery of naked DNA. Two days after injection liver samples were analysed for GFP fluorescence. The WT LDL receptor GFP protein was located on the cell surface whereas the W556S LDL receptor GFP protein was retained in intracellular compartments. Thus, the GFP-tagged LDL receptor protein allows both detailed time lapse analysis and evaluations in animals for the physiological modelling of mutations. This method should be generally applicable in functional testing of gene products for aberrant processing.

Lipid-binding proteins modulate ligand-dependent trans-activation by peroxisome proliferator-activated receptors and localize to the nucleus as well as the cytoplasm.

Peroxisome proliferator-activated receptors (PPARs) are activated by a variety of fatty acids, eicosanoids, and hypolipidemic and insulin-sensitizing drugs. Many of these compounds bind avidly to members of a family of small lipid-binding proteins, the fatty acid-binding proteins (FABPs). Fatty acids are activated to CoA esters, which bind with high affinity to the acyl-CoA-binding protein (ACBP). Thus, the availability of known and potential PPAR ligands may be regulated by lipid-binding proteins. In this report we show by transient transfection of CV-1 cells that coexpression of ACBP and adipocyte lipid-binding protein (ALBP) exerts a ligand- and PPAR subtype-specific attenuation of PPAR-mediated trans-activation, suggesting that lipid-binding proteins, when expressed at high levels, may function as negative regulators of PPAR activation by certain ligands. Expression of ACBP, ALBP, and keratinocyte lipid-binding protein (KLBP) is induced during adipocyte differentiation, a process during which PPARgamma plays a prominent role. We present evidence that endogenous ACBP, ALBP, and KLBP not only localize to the cytoplasm but also exhibit a prominent nuclear localization in 3T3-L1 adipocytes. In addition, forced expression of ACBP, ALBP, and KLBP in CV-1 cells resulted in a substantial accumulation of all three proteins in the nucleus. These results suggest that lipid-binding proteins, contrary to the general assumption, may exert their action in the nucleus as well as in the cytoplasm.

Development of a skin-based metabolic sink for phenylalanine by overexpression of phenylalanine hydroxylase and GTP cyclohydrolase in primary human keratinocytes.

Phenylketonuria, PKU, is caused by deficiency of phenylalanine hydroxylase (PAH) resulting in increased levels of phenylalanine in body fluids. PAH requires the non-protein cofactor BH4 and the rate-limiting step in the synthesis of BH4 is GTP cyclohydrolase I (GTP-CH). Here we show that overexpression of the two enzymes PAH and GTP-CH in primary human keratinocytes leads to high levels of phenylalanine clearance without BH4 supplementation. Integration of multiple PAH and GTP-CH transgenes were achieved after optimized retroviral transduction. Phenylalanine clearance was measured ex vivo in primary human keratinocytes cotransduced with PAH and GTP-CH (more than 370 nmol/24 h/106 cells), a level exceeding that of a human liver cell line (HepG2 cells). Cells overexpressing either one of the enzymes alone did not clear significant amounts of phenylalanine. Transfer of the two genes into the same cell was not necessary, since cocultivation of cells transduced separately with PAH and GTP-CH also resulted in phenylalanine clearance. Thus the experiments indicate metabolic cooperation between cells overexpressing PAH and cells overexpressing GTP-CH, possibly due to intercellular transport of synthesized BH4.

Telomere fluorescence measurements in granulocytes and T lymphocyte subsets point to a high turnover of hematopoietic stem cells and memory T cells in early childhood.

To study telomere length dynamics in hematopoietic cells with age, we analyzed the average length of telomere repeat sequences in diverse populations of nucleated blood cells. More than 500 individuals ranging in age from 0 to 90 yr, including 36 pairs of monozygous and dizygotic twins, were analyzed using quantitative fluorescence in situ hybridization and flow cytometry. Granulocytes and naive T cells showed a parallel biphasic decline in telomere length with age that most likely reflected accumulated cell divisions in the common precursors of both cell types: hematopoietic stem cells. Telomere loss was very rapid in the first year, and continued for more than eight decades at a 30-fold lower rate. Memory T cells also showed an initial rapid decline in telomere length with age. However, in contrast to naive T cells, this decline continued for several years, and in older individuals lymphocytes typically had shorter telomeres than did granulocytes. Our findings point to a dramatic decline in stem cell turnover in early childhood and support the notion that cell divisions in hematopoietic stem cells and T cells result in loss of telomeric DNA.

A polymorphic variant in the human electron transfer flavoprotein alpha-chain (alpha-T171) displays decreased thermal stability and is overrepresented in very-long-chain acyl-CoA dehydrogenase-deficient patients with mild childhood presentation.

The consequences of two amino acid polymorphisms of human electron transfer flavoprotein (alpha-T/I171 in the alpha-subunit and beta-M/T154 in the beta-subunit) on the thermal stability of the enzyme are described. The alpha-T171 variant displayed a significantly decreased thermal stability, whereas the two variants of the beta-M/T154 polymorphism did not differ. We wished to test the hypothesis that these polymorphisms might constitute susceptibility factors and therefore determined their allele and genotype frequencies in (i) control individuals, (ii) medium-chain acyl-CoA dehydrogenase-deficient patients homozygous for the K304E mutation (MCAD E304), (iii) a group of patients with elevated urinary excretion of ethylmalonic acid (EMA) possibly due to decreased short-chain acyl-CoA dehydrogenase activity, and (iv) in patients with proven deficiency of very-long-chain acyl-CoA dehydrogenase (VLCAD). No significant overrepresentations or underrepresentations were found in the first two patient groups, suggesting that the polymorphisms studied are not significant susceptibility factors in either the MCAD E304 or the EMA patient group. However, in the VLCAD deficient patients the alpha-T171 variant (decreased thermal stability) was significantly overrepresented. Subgrouping of the VLCAD patients into three phenotypic classes (severe childhood, mild childhood, and adult presentation) revealed that the overrepresentation of the alpha-T171 variant was significant only in patients with mild childhood presentation. This is compatible with a negative modulating effect of the less-stable alpha-T171 ETF variant in this group of VLCAD patients that harbor missense mutations in at least one allele and therefore potentially display residual levels of VLCAD enzyme activity.

Linking genotype to aorto-coronary atherosclerosis: a model using familial hypercholesterolemia and aorto-coronary calcification.

Most studies of the pathogenesis of coronary heart disease occur between gene variants and biochemical or physiological variables known to be atherogenic. In many situations, however, the gene products are not necessarily known. We studied 17 families (n = 122) with mutations in the low density lipoprotein (LDL) receptor gene as a model in which to test formally for linkage directly between an atherogenic genotype and ischemic heart disease (IHD) or aorto-coronary calcified atherosclerosis. In each family one of three different mutations was found: the Trp66-Gly mutation, the Trp23-Stop mutation, or a ten kilobase deletion removing exons 3-6 of the LDL receptor gene. Genomic DNA was used to determine these mutations by either enzymatic cleavage assays or Southern blotting. Aorto-coronary calcification was significantly associated with age and plasma cholesterol. Sex, hypertension, BMI and smoking were not associated with aorto-coronary calcification. Nonparametric analysis indicated significant linkage of the LDL receptor gene locus to aortic (p < 0.00005) and to aorto-coronary calcified atherosclerosis (p < 0.00001). Assuming a dominant mode of inheritance, significant linkage was detected for aortic (LOD = 3.89) and aorto-coronary calcified atherosclerosis (LOD = 4.10). We suggest that the atherogenicity of variations in other genes could be assessed by a similar approach.