Uses of Genetic Screening
- Some circumstances, e.g. in a pregnancy where there is a family history of a genetic disorder, may require individuals to determine if they have a particular allele present in their genome
- This can be determined by genetic screening
- There are three main uses of genetic screening
- Identifying individuals who carry an allele at a gene locus for a particular disorder
- The screening of embryos prior to implantation during fertility treatment; this is Preimplantation Genetic Diagnosis (PGD)
- Testing a foetus before birth; this is prenatal testing
Identification of carriers
- Carrier testing is offered to individuals with a history of genetic disorders in their family
- It can show whether people who have no symptoms carry the allele for particular disorders, such as cystic fibrosis
- Cell samples can be extracted from, e.g. blood or saliva, before being tested for the presence of specific alleles
- Couples can be tested prior to having children to determine the probability of future children inheriting the disorder
- Some of the benefits of carrying out genetic screening at this stage include
- Families can make informed decisions before having children
- Women can decide whether to have prenatal testing during pregnancy
Preimplantation Genetic Diagnosis (PGD)
- IVF, or in vitro fertilisation is a type of fertility treatment during which fertilisation is carried out in the lab; embryos produced in this way can be implanted into the uterus where they develop into a foetus
- Sometimes a couple might choose to have a child by IVF if they know that they are at increased risk of certain genetic disorders, as it allows them to screen any embryos produced using PGD
- PGD involves analysis of the DNA of an embryo prior to implanting it into the uterus
- The sample of DNA to be analysed can be obtained by taking cell samples from embryos produced during IVF
- Benefits of PGD include
- Evidence suggests that the process does not harm the embryo in any way
- Reduces the chances of having a baby with a genetic disorder
- It avoids abortion as it is carried out before implantation of the embryo
- It is worth noting that some people believe that an embryo is as worthy of human status as a foetus or a baby, so the discarding of affected embryos after PGD is not ethically straightforward for everyone
Prenatal testing
- Prenatal testing is offered to pregnant women with a family history of genetic disorders
- It involves testing the foetus for genetic diseases during the course of a pregnancy
- The DNA can be obtained by chorionic villus sampling or amniocentesis in the uterus
- Chorionic villus sampling
- This involves removing and testing a small sample of cells from the placenta using a fine needle
- The cells contain foetal DNA which can be analysed for genetic disorders, allowing parents to make informed decisions about the pregnancy and foetus
- Advantages of this process include
- It is carried out at around 11-14 weeks of pregnancy, so any problems can be picked up early on
- A relatively large tissue sample can be collected, providing plenty of cells to analyse
- Results are available rapidly
- Potential implications of chorionic villus sampling that should be considered include
- The process has a 1-2 % risk of miscarriage
- The process cannot pick up any disorders that are caused by alleles of genes located on the paternal X chromosome, as this chromosome is inactive in the placental cells sampled
- Amniocentesis
- This involves removing and testing a small sample of cells from amniotic fluid using a fine needle
- The amniotic fluid is the fluid that surrounds the foetus within the uterus
- The fluid contains foetal cells which contain DNA to be analysed
- Potential implications of amniocentesis that should be considered include
- It is carried out at around 15-20 weeks of pregnancy; this is relatively late in the pregnancy, making decisions about abortion more difficult for some parents
- The procedure has a 1 % risk of miscarriage
- It takes 2-3 weeks for results to be available
- This involves removing and testing a small sample of cells from amniotic fluid using a fine needle
- Benefits of prenatal testing include
- The tests allow parents to make informed decisions about the progress of a pregnancy
- Results can help parents prepare for the future care of the child, including medical treatment