B1.3 How can and should genetic information be used? How can we use our knowledge to prevent disease?
Different forms of the same gene are called ALLELES. You inherit one allele for each gene from your father and one allele for each gene from your mother. For example, the gene for eye colour has alleles for blue eye colour and alleles for brown eye colour. Your eye colour will depend on the combination of alleles you have inherited from your parents.
Some diseases are inherited from our parents though our genes: they are called GENETIC DISORDERS. They occur because of faulty or defective alleles.
E.g. CYSTIC FIBROSIS
Cystic fibrosis is caused by a recessive allele. You need to inherit two copies of the faulty allele to be born with cystic fibrosis. If you have just one copy, you are a CARRIER
Cystic fibrosis affects the cell membranes causing a THICK MUCUS to be produced in the lungs, gut and pancreas.
SYMPTOMS – Thick and sticky mucus
Breathing problems
Chest infections
Difficulty digesting food
HUNTINGTON’S DISEASE is another genetic that affects the central nervous system. However is caused by a dominant allele – the presence of just one dominant allele can cause the disease. You only need to inherit one copy of the faulty allele to have Huntington’s disorder, unlike cystic fibrosis, where you need to inherit both copies. You can inherit the disorder if one or both of your parents carry the faulty allele, because it is DOMINANT.
SYMPTOMS – Uncontrollable shaking
Clumsiness
Memory Loss
Inability to concentrate
Mood changes
GENETIC TESTING
- It is now possible to test adults, children and embryos for a faulty allele if there is family history of a genetic disorder. If the test turns out positive, the individual will have to decide whether or not to have children and risk passing on the disorder. This is called PREDICTIVE TESTING FOR GENETIC DISEASES.
- Genetic testing can also be carried out to determine whether an adult or child can be prescribed a particular drug without suffering from serious side effects. (TESTING AN INDIVIDUAL BEFORE PRESCRIBING DRUGS). E.g. certain people are highly prone to getting liver damage while taking COX-2 inhibitor drugs. A genetic test would ensure that only those patients who do NOT have the prone gene are prescribed the drug.
- Embryos can be tested for embryo selection. The healthy embryos that do not have the faulty allele are then implanted. This process is called in vitro fertilisation (IVF).
The process for embryo selection is called PRE-IMPLANTATION GENETIC DIAGNOSIS (PGD). After fertilisation, the embryos are allowed to divide into eight cells before a single cell is removed from each one for testing. The selected cell is then tested to see if it carries the allele for a specific genetic disease.
PGD has risks including inaccuracy in results-healthy embryo not being implanted and it may also decrease the chance of the embryo surviving once it has been implanted.
RISKS OF GENETIC TESTING:
However testing adults and foetuses for alleles that cause genetic disorders has implications that need to be considered, including:
- Risk of miscarriage as a result of cell sampling for the genetic test
- Using results that may not be accurate , including false positives and false negatives
- Whether or not to have children
- Whether or not a pregnancy should be terminated
- Whether other members of the family should be informed
There are ethical considerations that need to be considered very carefully
For example: governments may have the ability to impose genetic tests on individuals by implementing genetic screening programmes, but should they be allowed to do so? There is the potential for genetic testing to be used to produce detailed genetic profiles. These could contain information on everything from ethnicity to whether they are prone to certain conditions (e.g. obesity) or diseases (e.g. cancer).
However how will the information be used?
- Employers could potentially refuse to employ someone who possessed certain alleles
- Insurers may not cover a person who had genes that made them more likely to suffer a heart attack.