Loss of heterozygosity of the NOS3 dinucleotide repeat marker in atherosclerotic plaques of human carotid arteries

We have investigated 28 atherosclerotic plaques of human carotid arteries with a panel of 39 microsatellite markers for the presence of LOH. The objective of this research was to verify if LOH, described in association with tumorigenic process, could be involved also in benign fibroproliferative disease. Seventy percent of samples demonstrated allelic imbalance: 50% of cases showed LOH at a minimum of one locus, 3.5% at a minimum of two loci and 14.3% at three or more loci. The percentages of LOH ranged between 3.8 and 14.3% and the highest involved polymorphic marker is the NOS3 internal dinucleotide repeat. Our results indicate that, like tumorigenesis, the atherogenic process could also involve LOH mechanism. Furthermore, the finding regarding the NOS3 internal polymorphism suggests a possible role of the gene as cofactor in formation of the atheromas.

Blood fetal microchimerism in primary biliary cirrhosis

The autoimmune nature of primary biliary cirrhosis (PBC) is well established. We tested the hypothesis that fetal microchimerism indicated by the persistence of circulating fetal cells in women years after pregnancy might contribute to the aetiopathogenesis of PBC through a graft-versus-host-like response. We extracted DNA from the peripheral blood cells of 36 women carefully selected from 173 consecutive PBC patients, who were matched with 36 healthy women by age, age of last son, and number of children. Both patients and controls had to have male offspring, and no history of miscarriages or blood transfusions; they could not be twins. We tested all of the samples for the presence of two specific Y-chromosome sequences (SY154 and SRY) by amplifying DNA in a nested polymerase chain reaction. Y-chromosome-specific DNA was detected in the peripheral blood cell DNA of 13 (36%) of the 36 women with PBC and in 11 (31%) of the 36 healthy controls. The two groups of PBC patients with and without male DNA sequences were similar in terms of their clinical, biochemical, and serological features. Y-chromosome sequences were found in three of the four PBC women with associated systemic sclerosis. All of the 24 Y-positive samples contained SY154 sequences, but only three PBC patients and six controls showed the presence of both SY154 and SRY sequences. This discrepancy may suggest that not only fetal cells but also fragments of fetal DNA are present in maternal circulation. Overall, our data do not support the hypothesis that fetal microchimerism plays a significant role in the onset or progression of PBC.

Highly sensitive chemiluminescent method for the detection of cell contamination

Minisatellite analysis is commonly used in forensic disputes but can also be applied to the investigation of cell contamination. Such a problem arises, for example, when transplantation is performed. The presence of contamination has been investigated by other authors using radioactive methods. In the present study we describe a method that allows the detection of contamination with high sensitivity without using radioactive substances. Our technique is based on the use of polymerase chain reaction (PCR) amplification of minisatellite sequences (VNTR), followed by chemiluminescent detection. In particular, biotin-labelled dCTP is included in the PCR mixture and detection of PCR products is obtained following the CSPD chemiluminescent protocol (Southern-Light Nucleic Acid Detection Systems). We applied this method to artificial mixes of DNA of two individuals with alleles of different sizes. We performed progressive dilutions of an individual DNA into the other's DNA and revealed a contamination of 1 in 2500 cells. We also tested our technique searching for maternal contamination in cord blood samples in 60 cases and revealed a 18.3% contamination. The technique that we set up proves to be a very sensitive one which could be applied not only to the detection of maternal cells in cord blood but also in studying any other kind of contamination.

Cytogenetic abnormalities and microsatellite instability in endometrial adenocarcinoma

Recently various authors described a new mechanism involved in the genesis of some tumors, which is characterized by a tendency for replication mistakes and by genomic instability of microsatellite repeats. This instability can be revealed through the shift in the electrophoretic mobility of the analyzed fragments, which is due to a different number of repeat units. This phenomenon is widely documented in colorectal tumors of patients affected by hereditary nonpolyposis colorectal carcinoma (HNPCC). We performed a cytogenetic and molecular study of 23 endometrial adenocarcinomas to investigate the presence of genomic instability and to evaluate the possibility of a positive correlation with specific chromosomal changes. The study of genomic instability was performed using 23 microsatellites localized over 8 chromosomes. Genomic instability of microsatellites was observed in 3 cases over all 8 analyzed chromosomes. The tumoral stage of cases with microsatellite instability does not differ significantly from the remaining tumors. As a matter of fact several cases showing no evidence of instability were more advanced (II B, III A) than tumors with instability. In ten cases we observed trisomy of chromosome 10, in some as a sole anomaly. The 3 cases with genomic instability revealed a near-diploid karyotype and all showed the presence of a supernumerary marker derived from chromosome 1 rearrangements. A derivative chromosome 1 was revealed in 4 cases without evidence of microsatellite instability. It should be noted that the presence of many unidentified markers and the small number of tumors with instability do not allow us to give a definitive significance to this observation. Our results indicate that there is not an apparent correlation between microsatellite instability and specific chromosomal abnormalities. Moreover, we did not find any correlation between pathological characteristics of the tumor and genomic instability. Microsatellite instability appears to be a relatively rare event in endometrial carcinoma.

HIV-1 proviral DNA polymerase chain reaction detection in chorionic villi after exclusion of maternal contamination by variable number of tandem repeats analysis

OBJECTIVE

The study of the placental HIV infection in cases of seropositive pregnant women after exclusion of maternal contamination of chorionic villi samples by variable number of tandem repeats (VNTR) analysis.

METHODS

We studied 30 HIV-positive women: 17 terminated their pregnancy (11 in the first trimester and six in the second) and 13 delivered at term (one was a twin gestation). We selected chorionic villi and ruled out maternal contamination by VNTR analysis. DNA from chorionic villi and cord and maternal blood were tested for HIV by PCR. All infants underwent a paediatric follow-up.

RESULTS

All maternal blood samples tested positive for HIV-1 by polymerase chain reaction. No maternal contamination was revealed and HIV was found in six out of 11 first trimester placentas, in all second trimester samples, and in 10 out of 14 at term. Cord blood tested positive in all second trimester cases and in seven out of 14 liveborns. In no case was HIV found in cord blood without infection of the corresponding placenta; conversely, three placentas tested positive but cord blood was negative. Two infants were HIV-positive, 11 were uninfected (one case was lost to follow-up).

CONCLUSION

Our study indicates that HIV-1 can infect the placenta from first trimester onwards. HIV was found in two-thirds of our cord blood samples but it is possible that some viral DNA in cord blood may have come from infected placental cells. Additional studies are needed to assess the source of HIV in cord blood and the possible contribution of placental or maternal cells infected with HIV to vertical transmission of the virus.

Characterization of four microsatellites in an Italian population and their application to paternity testing

Microsatellites have recently been used for linkage analysis of genetic diseases and for DNA fingerprinting in forensic medicine. In the present study the heterozygosity, PIC values and allele distributions of four microsatellites, D8S85, D8S88, D5S346 and D7S460, in an Italian population have been investigated. After amplification with primers specific for each locus, alleles were separated and detected by denaturing gel electrophoresis and ethidium bromide staining. High heterozygosity and PIC values were observed for all microsatellites in accordance with data in other Caucasian populations. However, different allele distributions for D8S85, D8S88 and D5S346, due to the presence of additional bands or to different frequencies, were found. D7S460, which has never been fully characterized before, appeared to have five alleles in the range 172 to 188 bp. When used for paternity testing, all microsatellites gave results which were consistent with those obtained with established markers, including apo B 3'HVR, D1S80 and COL2A1. This indicates that D8S85, D8S88, D5S346 and D7S460 may be useful as additional informative markers or for solving discrepancies in selected cases.

Molecular screening of families affected by familial adenomatous polyposis (FAP)

OBJECTIVES

To assess the risk of developing familial adenomatous polyposis (FAP) in presymptomatic individuals using APC gene flanking and intragenic polymorphic markers.

SETTING

Twenty families enrolled in the Italian Registry of Polyposis comprising a total of 217 individuals, including 53 (24%) presymptomatic subjects with a 50% a priori risk of FAP, were analysed. Direct analysis techniques had previously failed to identify the FAP mutation in these families.

METHODS

DNA isolated from peripheral mononuclear blood cells and tissue sections was analysed by the polymerase chain reaction and a panel of seven highly polymorphic markers--YN5.64, CB83, CB26, LNS, APC1458.5, MBC, 37AB. Amplification products were separated by a modified denaturing gel electrophoresis method.

RESULTS

The haplotype associated with the disease was identified in 18 families (90%). The segregation of the FAP haplotype in these kindreds showed that 10 presymptomatic individuals had inherited the FAP mutation and carried a high risk of developing the disease. The remaining two families were not informative because of the lack of a sufficient number of probands or biological specimens.

CONCLUSIONS

These data indicate that indirect analysis with linked DNA markers has a high rate of success in defining the risk of FAP of presymptomatic subjects, provided that a sufficient number of probands or samples is available. Uninformative families accounted for 10% of the total, indicating that linkage analysis may still have higher sensitivity than direct mutation analysis techniques. The combined use of both approaches should be implemented, however, to enhance further the application of molecular genetics to the screening of families with FAP.

Chromosome 14 maternal uniparental disomy in the euploid cell line of a fetus with mosaic 46,XX/47,XX,+14 karyotype

We investigated the parental origin of the extra chromosome 14 and of the two chromosomes 14 of the euploid cell line, in a case of fetal mosaicism 46,XX/47,XX+14 diagnosed at amniocentesis. Molecular analysis of five polymorphic loci of the short tandem repeat type was performed. Markers D14S43 and D14S49 showed the presence of maternal uniparental disomy of chromosome 14 in the apparently normal cell line. The distribution of the markers analysed along the chromosome suggests maternal heterodisomy with a large isodisomic segment in the telomeric region, possibly caused by meiotic crossing-over.

Frequency of chromosomal aberrations after exposure to gamma-radiation of human chorionic villi

We investigated the chromosomal damage induced by in vitro exposure to gamma-rays of uncultured first trimester chorionic villi. Frequency and types of chromosomal aberrations at increasing doses of radiation have been evaluated on cytotrophoblast spontaneous metaphases obtained after a short term incubation. Our results indicate a direct correlation between radiation dose and aberration frequency.

Applicability of DNA isolated from syncytiotrophoblast vesicles to gene amplification and molecular analysis

Maternal contamination of fetal DNA represents a major problem when highly sensitive molecular techniques are used in the prenatal diagnosis of genetic diseases. For this reason, we have studied the possibility of using DNA isolated from syncytiotrophoblast vesicles as a target of gene amplification (PCR). Three PCR systems were selected which included a repetitive 149 bp fragment of the Y chromosome, the VNTR locus D1S80, and a portion of the beta-globin gene. The results of these experiments indicate that DNA isolated from syncytiotrophoblast vesicles is free of maternal contamination and is suitable for gene amplification and DNA analysis.