Prenatal diagnosis refers to the diagnosis of a developing fetus before birth. It helps clinicians determine whether the fetus is likely to have any genetic abnormalities and is especially useful in cases where there is a known family history of a certain disease.

A prenatal diagnosis can help parents and clinicians make healthcare decisions before a baby is born and, in some cases, help parents to decide whether or not to continue with the pregnancy.

Prenatal diagnosis and Rett syndrome

Rett syndrome is a rare neurodevelopmental disorder that is, in most cases, linked to mutations in the MECP2 gene in the X-chromosome. This gene encodes for a protein called methyl cytosine binding protein 2 (MeCP2) which is needed for brain development. Mutations in other genes, such as CDKL5 and FOXG1have also been linked to the disease but this is rare and results in so-called atypical Rett syndrome.

Prenatal diagnosis for Rett syndrome involves DNA testing to find out whether the developing fetus has a mutation in the MECP2CDKL5, and FOXG1 genes.

Rett syndrome mostly occurs as a result of a de-novo mutation, meaning that the defect is not inherited from the parents but appears spontaneously. Unknown genetic or environmental factors may increase the risk of such spontaneous mutations occurring in a certain family. In addition, a low percentage of familial Rett syndrome cases have been reported. In such cases, prenatal diagnosis is important to determine the genetic health of the fetus especially in families with a known history of the disease.

Although there is still some discussion on whether genetic testing for Rett syndrome should be a part of newborn and prenatal screening programs, there is a growing trend in the number of prenatal diagnostic tests for conditions such as Rett syndrome.

Prenatal diagnosis can help in the early identification of a disorder and enable proper planning for treatment and symptom management after birth. The results of prenatal genetic testing for Rett syndrome can also complement the clinical diagnosis of the disease after birth, then the pediatrician can classify the symptoms according to essential, supportive, or exclusion criteria.

Types of prenatal diagnosis

Several types of invasive and non-invasive prenatal diagnostic tests are available. Two commonly used methods are amniocentesis and chorionic villus sampling (CVS).

Amniocentesis is the process of drawing a sample of amniotic fluid, or the fluid surrounding the fetus, from the amniotic sac of the pregnant mother, usually between 15 to 20 weeks of pregnancy. The amniotic fluid helps to protect and cushion the developing fetus during pregnancy and is also an important diagnostic tool to help assess the fetus’s overall health. The amniotic fluid sample can be sent for genetic testing to determine whether the fetus has any genetic defects.

CVS involves taking a small sample of the placenta either through the mother’s cervix or abdomen. The placenta has the same genetic makeup as the growing fetus and hence can provide vital information about its genetic health. CVS can be performed as early as the 10th week of pregnancy but carries a slight risk of miscarriage and infection.

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