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Rapid DNA-based prenatal diagnosis by genetic linkage in three families with Alport's syndrome.

Alport's syndrome (AS) is a clinically and genetically heterogeneous progressive inherited glomerulonephritis characterized by hematuria, sensorineural hearing loss, ocular lesions, and specific alterations of the glomerular basement membrane. Typically, AS shows an X-linked dominant pattern of inheritance, with mutations affecting the collagen type IV alpha5 chain gene (COL4A5) at Xq22. Rarely, AS is caused in some families by mutations of the COL4A3/A4 genes on chromosome 2q, showing an autosomal recessive transmission. Very few families have been described with possible autosomal dominant AS, but no mutations in any of the COL4 genes have been found. We describe three unrelated families affected with a severe AS phenotype in which DNA-based prenatal diagnosis by linkage analysis was made in fetuses at risk for the disease. In two families, the pedigree structure and the clinical picture were consistent with typical X-linked dominant AS. In these families, autosomal inheritance was also ruled out molecularly. In one family, despite careful clinical and molecular evaluation, the mode of transmission could not be firmly established. We used tightly linked and intragenic COL4A5 markers, as well as COL4A3/A4-linked markers. A chromosome Y-specific marker for fetal sex determination was simultaneously used. In all the families, before the fetal analysis, the putative at-risk X haplotype was identified with high diagnostic accuracy. We diagnosed a healthy male fetus in one family, and female but carrier fetuses in the other two kindreds, who decided not to terminate their pregnancies. We used rapid nonisotopic polymerase chain reaction-based methods, and the results were available within 2 to 3 days. The genetic results significantly affected the reproductive decisions of the parents. This report illustrates the application of genetic linkage analysis as an additional tool for molecular diagnosis in AS, and also addresses the issue of the attitudes of the families toward prenatal testing. To our knowledge, prenatal diagnosis of AS using a genetic linkage approach has not been previously reported.

Adult↗

Women's decision-making in prenatal screening.

With serum screening (MS-AFP and hCG testing for Down's syndrome) women have to make several decisions in a limited time: whether to participate in the screening in the first place; then, if increased risk for fetal abnormality is detected, whether to have a diagnostic test, and finally, what to do if fetal abnormality is detected. The aim of this study was to examine how women themselves in an unselected population describe their decision-making in the different phases of serum screening. Women receiving a positive result from serum screening in two Finnish towns from September 1993 to March 1994 and a group of individually matched controls were invited to semistructured interviews; 45 index and 46 control women (79% of those invited) participated between their 29th and 37th weeks of gestation (mean 31 weeks). Although serum screening was most often presented as voluntary or as an option, half the women described participation as a routine or self-evident act; only one-fourth of the women described actively deciding about participation. After a positive screening result, women's reactions to diagnostic tests, and their intentions if disability would be detected, varied greatly. Most of the women actively decided about having diagnostic tests, but for 23% participation in diagnostic testing was called a self-evident act. Women's intentions regarding abortion varied from a firm decision to abort to a firm decision not to abort, and many remained ambivalent. Prenatal screening, which demands the making of several decisions in a limited time and is offered to all pregnant women as part of established maternity care, is not based on every participant's active decision-making and thus creates an ethical problem. This problem should receive special attention from those who develop, introduce and decide on new health care practices.

Abortion, Eugenic↗

Prenatal diagnosis of Menkes disease by genetic analysis and copper measurement.

Carrier detection for 12 women and prenatal diagnosis for six fetuses in Japanese families with a patient with Menkes disease (MNK) were performed by gene analysis and/or measurement of the copper concentration in cultured cells. Six out of eight mothers of MNK patients were carriers while two (25%) were not carriers. Two unrelated patients showed the same mutation (R986X): one patient's mother was a carrier while the other was not. One male and three female fetuses did not have the same mutant allele as the respective MNK proband and have been healthy since birth. One female fetus had the same mutant allele as her affected brother. Gene analysis is very useful and reliable, although such examination is only indicated in families in which a mutation has been identified. In one family in which a mutation in ATP7A was not found, cultured amniocytes from a male fetus had a high copper concentration. Thus after his birth, the biochemical findings confirmed the presence of MNK and early treatment was started. As his early treatment with parenteral copper-histidine prevented the neurological disorders effectively, prenatal diagnosis is very important.

Amniocentesis↗

Vasculogenesis in early human placental villi: an ultrastructural study.

In this study we examined the chorionic villi of 5 normal human placentas at 12-14 weeks of gestation ultrastructurally with regard to differentiation of the vascular components. The aim of the present report is to discuss the factors influencing vasculogenesis (in situ formation of blood vessels) at the ultrastructural level. Our observations have led us to think that the cytotrophoblast influences vasculogenesis in human chorionic villi. Mesenchymal-preendothelial cell groups were always found in very close association with the cytotrophoblast at the periphery of the villi, forming blood vessels. The cytotrophoblast probably attracts mesenchymal cells towards the margin of the villi by secreting vascular endothelial growth factor (VEGF). Once cells attach to the trophoblastic basement membrane they begin to differentiate into endothelial cells. This close structural relation between two cell types (cytotrophoblast and mesenchymal cells) may not be the only mechanism controlling vasculogenesis, but it seems to be one of the factors influencing the differentiation of mesenchymal cells into the endothelial cells of blood vessels in early human chorionic villi.

Blood Vessels↗

Prenatal diagnosis in merosin-deficient congenital muscular dystrophy.

Prenatal diagnosis was carried out in five merosin-deficient congenital muscular dystrophy (CMD) families. We studied both laminin-alpha 2 chain expression in trophoblast using immunocytochemistry and linkage analysis to the LAMA2 locus. In four families there was good agreement between the immunocytochemistry and linkage analysis results: in one case the trophoblast was negative for LAMA2 expression and haplotype analysis suggested the foetus was affected; in the other three cases the laminin-alpha 2 chain expression was normal and foetuses were found to be carriers. In the remaining family, a case of partial laminin-alpha 2 chain expression, the immunostaining of the trophoblast was weaker compared to the control. Linkage analysis, however, could not be performed because of maternal DNA contamination. After termination of pregnancy, the foetal muscle was studied and suggested weak laminin-alpha 2 chain expression. The haplotype analysis however showed that the foetus was probably a carrier, unless a double recombinant event had occurred. We conclude that a combination of immunocytochemistry and linkage analysis can be used for the prenatal diagnosis of merosin deficient CMD. The results are easy to interpret in families with total absence of the protein, while caution is required when dealing with families where partial expression occurs.

Antibodies, Monoclonal↗

Prerequisites and strategies for prenatal diagnosis of respiratory chain deficiency in chorionic villi.

Prenatal diagnosis for respiratory chain deficiencies is a complex procedure that requires a thorough diagnostic work-up of the index patient. This includes confirmation of the clinical and metabolic evaluations through histological and enzymatic examinations of tissue biopsies. Prenatal diagnosis currently relies on biochemical assays of respiratory chain complexes in chorionic villi or amniocytes and is possible by mutation analysis of nuclear genes in a limited but increasing proportion of cases. Based on a recent survey of prenatal diagnosis in families with complex I and complex IV deficiencies, performed at Nijmegen Centre for Mitochondrial Disorders (NCMD), prerequisites and strategies for performing prenatal diagnosis have been developed to increase reliability. Biochemical investigations in chorionic villi can be done reliably if the respiratory chain enzyme deficiency is expressed in both skeletal muscle and skin fibroblasts to rule out tissue specificity. No mitochondrial DNA defects must be suspected or established. The NCMD does not offer prenatal diagnosis until all the prerequisites have been confirmed. We expect prenatal diagnosis at the molecular level to become more feasible in time as the mutational spectrum broadens with advances in medical research.

Adult↗

[Genetic testing in pregnancy].

First trimester risk screening is probably the major methodological advance in identifying pregnancies at increased risk for genetic disease during recent years with an impact on all pregnancies. The high detection rate with moderate false positive rates will reduce the over-all number of invasive procedures as compared to the traditional approach based on maternal age exclusively, in particular considering the demographic shift towards higher mean maternal age. Non-invasive prenatal diagnosis from fetal cells or DNA in the maternal circulation remains an experimental approach, despite a growing number of reports on successful diagnoses of single gene disorders. In the lab molecular cytogenetic approaches have considerably broadened the diagnostic spectrum of conventional karyotyping and facilitated a rapid diagnosis of selected frequent aneuploidies. Molecular genetic testing, in particular on chorionic villi, allows an early and reliable diagnosis of a growing number of severe monogenic conditions. A restrictive legislation has hampered the development of preimplantation genetic diagnosis in German speaking countries, only a few groups work on polar body diagnosis, a legal but restricted alternative.

Adult↗

Twin pregnancy: the role of ultrasound in management.

Determination of chorionicity is one of the most important issues in the management of twin pregnancy. Modern ultrasound equipment has made it possible to accurately assess placentation already in the first trimester with the lambda sign. With regard to prenatal diagnosis, it is important to know the chorionicity in order to calculate the risk of chromosomally abnormal fetuses. Accurate chorionicity offers the obstetricians the opportunity to observe the monochorionic twins more intensively than is required for twins with dichorionic placentation. This review gives an update of the state of the art for clinicians caring for twin pregnancies.

Amniocentesis↗

Marfan syndrome as a paradigm for transcript-targeted preimplantation diagnosis of heterozygous mutations.

Among the many clinical applications of the polymerase chain reaction (PCR) is its potential use in preimplantation diagnosis of genetic disorders. Performing PCR on single blastomeres from early cleavage stage (six- to eight-cell) human embryos should, in principle, enable reliable determination of disease status for certain inherited conditions. However, reports of misdiagnoses using this technique have diminished enthusiasm for its widespread clinical use. One principal source of error is the propensity for genome-targeted PCR to exclusively amplify one allele in reactions assaying a single heterozygous diploid cell. Complete reaction failure is also common. Employing the Marfan syndrome (MFS) as a paradigm, we have developed a reliable, reverse transcription-PCR-based method of genotyping single cells that overcomes these obstacles. The technique should facilitate accurate preimplantation diagnosis of MFS and other selected genetic diseases caused by heterozygous or compound-heterozygous mutations.

Artifacts↗

Inverted duplications: how many of them are mosaic?

The best-known situation indissolubly linked to mosaicism is the uniparental disomy where a trisomic or monosomic zygote develops at least one cell line with 46 chromosomes. The mosaicism normal/abnormal cell lines may remain confined to placenta or persist in the embryo. Here, we describe a second situation that might also be indissolubly linked to a mosaic condition or at least to a confined placental mosaicism. We analysed the case of a mosaicism del(8p)/inv dup(8p) found in prenatal diagnosis. We had already demonstrated that the first product of the abnormal meiotic recombination at the basis of the inv dup rearrangements is a dicentric chromosome. Its breakage leads to the formation of a deleted and an inv dup chromosome. Although we had previously assumed that the dicentric underwent a breakage at meiosis II so that the zygote inherited the inv dup chromosome, our findings and those of others indeed indicate that the dicentric may be inherited in the zygote and that it might persist as such in early postzygotic stages, then undergoing different breakages in different cells leading to different abnormal chromosomes, either deleted or duplicated. Selection versus the most viable cell line(s) results either in a confined placental mosaicism with the inv dup cell line as the only one present in the embryo or in children with both the deleted and the inv dup cell lines. Phenotype/karyotype relationships in inv dup rearrangements must also take into account the influence of the other abnormal cell line during embryogenesis.

Aborted Fetus↗

Prenatal diagnosis in combined antithrombin and factor V gene mutation.

We report prenatal diagnosis in a family with combined antithrombin deficiency (type II heparin binding site) and factor V 506 Arg to Gln mutation. Both clinically unaffected parents are heterozygous for the antithrombin mutation, which results in a 99 Leu to Phe substitution, and the father is also heterozygous for the factor V gene defect. There is one daughter, homozygous for the antithrombin and heterozygous for the factor V mutations, who suffered a right-sided hemiparesis at the age of 4 months due to occlusion of the left middle cerebral artery and a large left sided infarct followed by further thromboembolic events. The family requested prenatal diagnosis and chorionic villi was sampled at 12 weeks gestation. The fetus was shown to be heterozygous for the antithrombin and factor V gene mutations, the same genotype as the unaffected father. No further intervention was considered necessary. To our knowledge this is the first report of prenatal diagnosis in antithrombin deficiency.

Antithrombins↗

Congenital and perinatal infections with cytomegalovirus.

Congenital cytomegalovirus (CMV) infections remain the leading viral cause of congenital malformations in the developed world. Despite advances in our knowledge, the epidemiology and natural history of congenital CMV infection are still poorly understood, particularly in Australia. Congenital CMV causes illness ranging from no clinical disease (asymptomatic, but infected) through to prematurity, encephalitis, deafness and haematological disorders and death. Perinatal CMV acquisition usually results in less severe illness including asymptomatic infection, acute infection with hepatitis, fever, and pneumonitis. CMV infects only humans, and in vitro and in vivo models for intrauterine infection are required in order to test new treatments, and better describe the pathogenesis of congenital CMV. Using new knowledge of the epidemiology and natural history of CMV, treatment regimens during late pregnancy are currently undergoing clinical trial although no definitive recommendations are available.

Amniocentesis↗