Genetic screening and gene therapy

what are people with a single allele for a mutation called 

carriers 

why is Huntington’s disease different to other genetic diseases

caused by a dominant allele on chromosome 4, very rare but a heterozygote will go onto develop disease

what is breast cancer predominantly cause by

mutated tumor suppressor genes BRCA1 and BRCA2

what can genetic screening allow

• avoid having offspring with a genetic disease

• Avoid late abortions if genetic disease discovered later in pregnancy 

• Allow couples to have children who would otherwise choose not to

What is prenatal screening

used to test for genetic conditions of an unborn child

What does preimplantation genetic diagnosis (PGD) involve

involves removal of cell from embryo formed in vitro and check of its alleles

What are the two ways in which a foetus can be genetically screened

Amniocentesis and chorionic villi sampling

What is involved in amniocentesis, when during pregnancy and what does it determine 

• sample of amniotic fluid obtained at 15-16 weeks 

• Determines chromosomal status of foetus for large chromosomal mutations 

What is involved in chorionic villi sampling, when during pregnancy and why can it be better than amniocentesis

• 10-13 weeks, before woman has felt foetal movements

• Small sample of placenta (chorionic villi) removed

• Richer in foetal cells so results returned more quickly

What are the risks of amniocentesis and CVS

Increase miscarriage by 1-2% from 2-3% at up to 12 weeks of gestation

What are the ethical arguments against genetic screening

• may disagree with certain religious beliefs

• Viable embryos can be discarded

• Could lead to change other characteristics

• Anxiety

• May not develop condition

How does gene therapy work 

treats genetic diseases caused by faulty (usually recessive) allele by inserting a functional copy of allele into cells using a vector

What can be used as a vector during gene therapy

• liposomes (small spheres of phospholipid) coat plasmids

• Viruses such as adenovirus (DNA) or retroviruses (RNA) which use reverse transcriptase to insert functional allele.

What is the difference between gene therapy to somatic and germ line cells

• somatic (body) cells - changes temporary as cells die and not replaced by new cells, no passed onto offspring

• Germ line cells (involved in sexual reproduction - gametes or embryo) - illegal as changes passed onto offspring

What is Leber Congenital Amaurosis

genetic condition, born with poor eyesight which deteriorates causing loss of vision in childhood

how can babies born with Leber Congenital Amaurosis be treated using gene therapy

In vivo somatic gene therapy to insert normal allele using adenovirus improving sight

How can a patient with SCID be treated using gene therapy

• some of patients stem cells were removed (ex vivo) and normal allele for ADA gene was inserted using viral vector.

• Cells reintroduced to patients body to mature to T/B cell