Genetic Screening using CF as an example Word Count: 1497
Genetic screening is a very useful medical technique used to identify abnormal changes in chromosomes, genes or proteins. Genetic screening is used in several tests with more than 1000 available tests today, and more are being developed. (1) The outcomes of a genetic screening test can be used to identify a person’s chance of obtaining a genetic disease or passing on an inherited disease such as cystic fibrosis or help people make family decisions such as having children, having an abortion or even marriage. There are several types of genetic screening methods used today; some are carried out when making family decisions such as identification of carriers whilst others are used prior to birth during pregnancy such as prenatal screening or even some that are done before pregnancy such as preimplantation genetic diagnosis.
Genetic screening is being increasingly used in adults with cystic fibrosis as an approach to make certain that families do not pass on the disease by letting families be able to make informed decisions about having children if they are carriers of the disease. It is also used in very young newborn babies in order to carry out treatment as soon as possible if a baby has cystic fibrosis.
Identification of carriers is usually carried out if one member of a family is born with cystic fibrosis as this will help other members of a family to identify whether or not they are carriers of the disease and thus allowing them to make informed decisions in their future. An identification of carriers test is conducted by taking a small sample of blood or some cells from the inside of the mouth can be used to carry out a simple test to identify the mutations in the CFTR alleles for cystic fibrosis. (2) In couples, if one partner knows that they are a carrier after a identification screening, the other partner is also advised to get tested as in the case of recessive diseases such as cystic fibrosis, if both partners are carriers then there is a 25% chance of passing on the disease. This type of screening is appropriate because if a couple knows their chances of having a child with cystic fibrosis then they can have an informed decision on whether or not to risk having a child or to consider other ways such as adoption or preimplantation genetic diagnosis.
Prenatal methods such as amniocentesis are used during pregnancy to see whether a child has the homozygous recessive genotype that will cause cystic fibrosis. During an amniocentesis screening test, 20cm3 of amniotic fluid that surrounds the fetus is removed using a needle and syringe as shown in image A. The procedure is done under ultrasound guidance so that the operator can see exactly where the needle goes and to make sure the baby isn’t harmed. It is carried out in the 16th week of pregnancy and the collected amniotic fluid sample is placed in a centrifuge to separate the fetal epithelial cells and the blood cells. After separation, the fetal epithelial cells can be cultured for 2-3 weeks and a number of genetic defects can be tested for and in the case of cystic fibrosis the cultured sample is tested for faulty CFTR alleles. Although this is a valid method in identifying whether or not a child will have cystic fibrosis, it does contain many disadvantages. Results are only available three weeks after the test, it is carried out late in pregnancy and thus if a mother chooses to have an abortion after the results could be more traumatic and painful for the mother. Furthermore, there is a small percentage of miscarriage spontaneous to the test and thus there is a risk for the mother and unborn baby. Besides these disadvantages, there are many advantages for example, if a baby is found to possess cystic fibrosis then planning can be taken to help the child from day one of birth. Additionally, as an ultrasound is used during the screening process, the process can also be used to check on the ‘general well being of a baby’ and its gender can be accurately identified in the process. (3)