1. Prenatal Diagnosis of Chromosomal Disorders - Molecular Aspects

It is known that perinatal mortality is caused in 20-25 percent of cases by inhaerited anomalies of fetuses and many of theese might be explained by genetic disorders. In general genetic disorder is a condition caused by abnormalities in genes or chromosomes. Chromosomes are complex bodies in cell nucleus as carriers of genes. While some diseases are due to genetic abnormalities acquired in a few cells during life, the term "genetic disease" most commonly refers to diseases present in all cells of the body and present since conception. Some genetic disorders are caused by chromosomal abnormalities due to errors in meiosis, the process which produces reproductive cells such as sperm and eggs. Examples include Down syndrome (extra chromosome 21), Turner Syndrome (45X0) and Klinefelter's syndrome (a male with 2 X chromosomes). Other genetic changes may occur during the production of germ cells by the parent. One example is the triplet expansion repeat mutations which can cause fragile X syndrome or Huntington's disease. Defective genes may also be inherited intact from the parents. In this case, the genetic disorder is known as a hereditary disease. This can often happen unexpectedly when two healthy carriers of a defective recessive gene reproduce.