The genetic counsellor

• When there is a possibility that a couple may have a child with a genetic disease, they may be referred to a genetic counsellor (usually by physician with knowledge of condition)

• Couple likely to be referred if:– Either has family history of genetic disease– They belong to a group known to have a high risk

of genetic disease (ex: group in which marriage between close relatives is common)

The genetic counsellor

• Couple likely to be referred if:– History of recurrent miscarriages– Woman is over 38 (high risk of Down Syndrome)– Pregnancy is high risk

The genetic counsellor

• Role of counsellor is to provide couple with info about risks involved with them having children

• Genetic counsellors help with probability or chance that children will inherit genetic disorders

The genetic counsellor

• If there is a family history, sometime the genetic counselor may take a tissue sample from the parents and run a genetic screen to test for recessive alleles– This is called genetic screening

• Counselor uses pedigree analysis to track family history of inheritance

• Blood testing combined with pedigree analysis provides the most accurate prediction tools

Genetic screening

• Analysis of a person’s DNA to check for the presence of a particular allele

• This can be done in adults, in a fetus or embryo in the uterus, or in an IVF embryo

Genetic screening

• In 1989 the first ‘designer baby’ was created• Officially known as pre-implantation genetic

diagnosis (PGD) the technique involves the normal IVF procedure for fertilization, but at the 8 cell stage, one of the embryo’s cells is removed

PGD

• The cells removed from the embryos are genetically screened for genetic disorders, and embryos with alleles for the disorders are discarded

• PGD is used to prevent children from developing fatal or debilitating disorders– In 2004 in the UK, it was used to produce a tissue

match for an older sibling with genetic disorder

Genetic screening

• PGD provides prospective parents with very difficult ethical dilemmas if a fetus is found to have genetic conditions– The decision about whether or not to terminate a

pregnancy presents parents with an extremely difficult ethical issue to consider

Somatic and germ cell therapy

• Gene therapy involves introducing the ‘correct’ allele into a person’s cells– So far, all gene therapy has involved placing the

allele in body cells, known as somatic cells– Not completely effective

• However, another possibility would be to insert the allele into germ cells (gametes)

Somatic and germ cell therapy

• Germ cell gene therapy is presently illegal in humans

• However, it has successfully been done successfully in other animals– Although it looks like there is a high chance that

these offspring develop other unpredicted disease

Germ cell therapy

• Problem with germ cell therapy is that all of the cells of the child will be produced from this genetically engineered germ cell, and therefore all cells will carry the inserted gene

• When the child grows up and reproduces, their gametes will contain the altered genetic code, passing it on to their offspring

The ethics of genetic screening

• Embryos can be genetically screened, but not genetically altered

• there is still debate over the practices of genetic screening techniques, primarily that of:– Amniocentesis– Chorionic villus sampling

Amniocentesis

• A sample of amniotic fluid is obtained at 15-16 weeks of pregnancy

• Sample obtained through ultrasound scanning to visualize the position of the needle and amniotic sac/fetus

• The sample and be used for genetic screening to look for chromosomal mutations

• 1% risk of miscarriage

Chorionic villus sampling

• Can be carried out between 10-13 weeks of pregnancy (allows for earlier warning)

• Small sample of the placenta known as the chorion is removed by a needle

• Higher risk of miscarriage than amniocentisis. Typically 2-3%