Diagnosis and prevention of chromosomal disorders

Simão, Laurentino

http://hdl.handle.net/10400.18/4400

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Authors

Simão, Laurentino

Abstract(s)

Clinically significant chromosomal defects occur in 0.65% of all births, with high morbidity and mortality. Chromosome disorders form a major category of genetic disease. They account for a large proportion of all reproductive wastage, congenital malformations, and mental retardation and play an important role in the pathogenesis of malignancy. Specific chromosome abnormalities are responsible for more than 100 identifiable syndromes. The strategies followed in cytogenetics have changed over the past 25 years, moving from the exclusive use of classical cytogenetic methods (karyotyping) to the use of molecular biology methods (molecular cytogenetics and cytogenomics). The cytogenetic studies deserves a great attention since allows identifying the chromosomal abnormalities behind the congenital anomaly. This fact allows establishing genotype-phenotype relationships and the cause and prognosis of pathological pregnancies and population genetic diseases. The utility of studies in prenatal diagnosis (PND) and in patients with chromosomal disorders extends to the possibility of intervening in the diagnosis, prognosis and prevention of the genetic disease, as illustrated with the presentation of some case studies in the laboratory, that also assesses the value of new techniques implementation in a cytogenetic laboratory in order to obtain a complete result. In the other hand, the analysis of retrospective case series with an epidemiological approach contributes to the knowledge of the etiological cause of certain groups of chromosomal abnormality. For instance, Down Syndrome (DS) is the most common chromosomal disorder and the most common cause of moderate mental retardation. It is the most frequent abnormality in PND and is even one of the reasons for its implementation. We carried out a large study on the last 20000 PND we received in the laboratory. 2% showed karyotype compatible with DS. An increased number of karyotypes with DS were detected since chorionic villus sampling (CVS) started to be received in the laboratory. The implementation of rapid aneuploidy detection methods in PND also allowed a faster reporting time of trisomy 21. However, one question remains in discussion: pregnancies affected by DS have a great risk of spontaneous fetal loss during the first trimester and earlier second-trimester. Thus, some CVSs in DS cases will result in spontaneous miscarriages. These thematic show the role of chromosome abnormalities in the diagnosis and prevention of the genetic disease and also the complexity of the ways that we choose.