Single gene testing may be performed on amniocentesis or CVS sample if a specific gene abnormality is suspected because of:
1. very unique features on ultrasound scan
2. previous history of such a specific gene abnormality in a previous baby where parents were found not to have carry similar genes (usually such cases are counselled that there is a 1-2% risk of recurrence)
3. family history of a genetic disease where:
a) both parents are known to be carriers of a known autosomal recessive condition e.g.
b) one of the parents are known to be affected by an autosomal dominant condition e.g.
c) the mother is known to be a carrier of an X-linked recessive condition and the fetus is
male e.g. haemophilia A
The main advantages of doing a single gene testing are that:
1. only a specific genetic test is performed, and hence avoids the difficulty sometimes of interpreting variants of unknown significance when using more exploratory tests like whole exome sequencing and whole genome sequencing
2. generally cheaper than whole exome sequencing or whole genome sequencing
The main disadvantage of doing a single gene testing is that other genetic diseases are not tested by a single gene testing, and hence would not be discovered by such a test. This would include other genetic conditions not suspected by the doctor.