Best practice guidelines, which are applicable to PCR-based prenatal genetic testing for any monogenic disorder, include:
1. To divide the original CVS or amniotic fluid samples to two aliquots, so the fetal DNA can be analyzed in duplicate. In addition when CVS is the source of fetal genetic material, to perform careful microscopic dissection (see below in the protocols for preparation of fetal samples in 17.5).
2. To obtain fresh parental blood samples along with the fetal sample in order to confirm parental mutations and also as a source of control DNA.
3. To analyze parental DNA samples and other appropriate controls for the relevant disease-causing mutations alongside the fetal DNA.
4. To repeat the fetal DNA analysis to double check the result, ideally by using a second independent method.
5. To exclude presence of contaminating maternal DNA in the fetal sample through analysis of appropriate hypervariable genetic markers (e.g. microsatellite loci) in the parental and fetal DNA; the fetal DNA should demonstrate inheritance of one maternal and one paternal allele for any loci tested.
6. Finally, the PND report should detail the methods of DNA analysis used and state the risk of misdiagnosis based on the literature and the audit results of the diagnostic laboratory.
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