Practise medical genetic technology by comparing recombinant-protein treatments, interpreting screening choices and weighing gene-therapy benefits and risks.
One cause of the genetic disease severe combined immunodeficiency (SCID) is a mutation in the ADA gene. This mutation results in a deficiency of the enzyme adenosine deaminase (ADA).
Although ADA is found throughout the body, it is especially active in lymphocytes. The absence of functional ADA causes the build-up of toxic metabolites that kill lymphocytes and damage organs.
Babies are often diagnosed with SCID by six months old. Treatment can greatly improve the life expectancy of children with SCID.
Some treatment options are available.
- Enzyme replacement therapy with recombinant human ADA made by genetically modified (GM) Escherichia coli. Weekly intra-muscular injections are given.
- Bone marrow transplant if a well-matched donor, such as a close relative, can be found.
- Gene therapy.
Suggest and explain why it may be more appropriate to use enzyme replacement therapy to treat SCID instead of a bone marrow transplant.
Outline the procedure used for gene therapy treatment of a person with SCID.
Suggest the social and ethical implications of gene therapy for SCID that need to be considered before treatment is carried out.
The polymerase chain reaction (PCR) is used to produce large quantities of DNA from a very small original sample. The main steps of one PCR method are shown in Fig. 4.1.
Fig. 4.1
The presence of a faulty allele of the gene B R C A 2 can lead to an increased chance of developing breast cancer. There are many different faulty alleles of the gene BRCA2.
People who are considered to be at risk of breast cancer may choose to be tested for the presence of these alleles in their genomes.
A microarray can be used to test blood samples for the presence of these alleles. The microarray contains DNA probes for different faulty alleles of the BRCA2 gene.
Outline the advantages of screening for faulty alleles of the BRCA2 gene.