What is Molecular DNA testing

Almost every cell in the body contains DNA, which can be extracted from various sources, including cheek cells, blood, hair roots, semen and body tissue. The genetic code of a particular gene can be tested to look for particular abnormalities. It is also possible to identify a person on the basis of their DNA. When PCR technology (see below) is used for testing, usually only a small sample is required. Molecular Genetic Prenatal Diagnosis testing requires the same sampling as for chromosome testing (see Prenatal diagnosis: chorionic villus sampling and amniotic fluid sampling).

PCR

PCR stands for polymerase chain reaction and is a routine technique employed for genetic testing. PCR is used to amplify a targeted DNA region or sequence (e.g. gene) of interest. Once the PCR has been completed a genetic analyser is used to determine the size of the amplified DNA (gene). By determining the size, molecular scientists can tell whether a gene has a particular error (mutation) or not.

Alternatively, a genetic analyser can determine the sequence of DNA molecules in a gene, otherwise known as gene sequencing.

Diagnostic testing – Disease diagnosis or carrier status

Testing for a particular abnormality of a gene is usually performed if there is a medical diagnosis of a genetic disease, or a family history of a genetic disease in your family (e.g beta-Thalassaemia, haemophilia, Huntington disease), or if you have a significant risk of being a carrier of a genetic disease (e.g Caucasians have a risk of 1 chance in 25 of carrying a faulty gene for cystic fibrosis). Diagnostic DNA testing can test for a particular abnormality or screen for the most common mutations, depending on the disease type. Carriers of a disease may be offered prenatal diagnosis to test if a pregnancy is affected, or a special test to diagnose embryos (preimplantation genetic diagnosis) may be possible (see www.sydneyivf.com).