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04 July 2016

#160 Genetic screening

Genetic screening: analysis of a person's DNA to check for the presence of a particular allele
* available for adults, fetus, embryo,...








- BRCA1 and BRCA2: faulty alleles that lead to breast and ovarian cancer in females and breast cancer in males ---> elective vasectomy


- pre-implantation genetic diagnosis (PGD):

  • carry out the IVF procedure (sperm and egg in a dish)
  • when it reaches the 8-cell stage, remove one cell and analyse the DNA for disease alleles
              - disease allele absent: embryo chosen for implantation
              - disease allele present: embryo is discarded
---> avoid pregnancies with haemophilia, sickle cell anaemia, Huntington's disease, cystic fibrosis,...


  • provides information about the increased risks of people having genetic conditions
  • people prepare for the late onset of genetic conditions like Huntington's disease
  • identify whether embryos from IVF will develop genetic conditions
  • identify a fetus that needs early treatment
  • helps provide early diagnosis

Ethics of genetic screening
  • fetus screening for genetic disease:
             - amniocentesis: look for chromosomal mutations
             - chorionic villus sampling (although there is an increased risk for miscarriage with this)
  • sex preselection: terminates pregnancy if the embryo is of the wrong sex (used PGD to select)
  • therapeutic abortions: terminating pregnancies for medical reasons




Syllabus 2016-2018

19.2 Genetic technology applied to medicine

a) define the term bioinformatics 

b) outline the role of bioinformatics following the sequencing of genomes, such as those of humans and parasites, e.g. Plasmodium (details of methods of DNA sequencing are not required) 

c) explain the advantages of producing human proteins by recombinant DNA techniques (reference should be made to some suitable examples, such as insulin, factor VIII for the treatment of haemophilia and adenosine deaminase for treating severe combined immunodeficiency (SCID)) 

d) outline the advantages of screening for genetic conditions (reference may be made to tests for specific genes such as those for breast cancer, BRCA1 and BRCA2, and genes for haemophilia, sickle cell anaemia, Huntington’s disease and cystic fibrosis) 

e) outline how genetic diseases can be treated with gene therapy and discuss the challenges in choosing appropriate vectors, such as viruses, liposomes and naked DNA (reference may be made to SCID, inherited eye diseases and cystic fibrosis) 

f) discuss the social and ethical considerations of using gene testing and gene therapy in medicine (reference should be made to genetic conditions for which treatments exist and where none exist, also to IVF, embryo biopsy and preselection and to therapeutic abortions) 

g) outline the use of PCR and DNA testing in forensic medicine and criminal investigations

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