Teacher FAQs

What is PGD?
  • Pre-implantation genetic diagnosis is a set of procedures that can be carried out on embryos prior to fertilization 
  • It is a method used to determine whether the embryos are at risk of developing a genetic condition that could possibly lead to disease

What is the difference between genetic screening and pre-implantation genetic diagnosis?
  • Genetic screening is the general term given to all tests for genetic disorders
  • Screening is broadly divided into four groups 
        • Adults
        • Newborn
        • Antenatal
        • PGD

    When was PGD first used?
    • 1989 to determine the gender of an embryo
    • Region of Y chromosome amplified using PCR (polymerase chain reaction) to select against the male embryos due to their susceptibility to ‘sex-linked’ illnesses

    How are the embryos prepared?
    • PGD cannot be used for natural conceptions and therefore begins with in vitro fertilisation (IVF)
    • Embryos are usually screened 3 days after fertilization, when they consist of 8 cells
    • A hole is made in the jelly layer surrounding the embryo and one or two cells, known as blastomeres, and are removed using a fine pipette

    What are the methods for analysis?
    • The nature of the problem depends on the test that is carried out on the embryo
    • For problems at one specific gene, Polymerase Chain Reaction (PCR) based methods are used
          • Creation of millions of copies of a specific section of DNA (amplification) without having to create new cells
    • For checking whether an embryo has the correct number of chromosomes or testing the gender of an embryo, Fluorescence In Situ Hybridisation (FISH) or Comparative Genome Hybridisation (CGH) is used
    What are some examples of diseases can PGD can be used?
    • Cystic fibrosis, sickle cell anaemia, haemophilia
    • Beta-thalassemia, spinal muscular atrophy
    • Huntington’s disease
    • X-linked diseases such as fragile X syndrome, Duchenne muscular dystrophy

     

    What are other uses of PGD?
    • Sex Selection
          • This involves selecting the gender of a child for non-medical reasons
          • It is currently illegal under HFEA in the UK however is carried out in the United States
          • Cases include the Masterton family, who already had 4 sons and a daughter who died. They wished to have another daughter and were not allowed to do so in the UK even though it was self-funded
    • Aneuploidy
          • Aneuploidy - A number of abnormal chromosomes
          • Extra or missing chromosomes are a common cause of genetic diseases

     

    PGD for the diagnosis of genetic diseases

    • Video  ‘Genetic advance raises health hopes’ – BBC News, 26th Aug 2009
    What are Mitochondrial diseases?
    • Mitochondrial disease is a neuromuscular disease which is caused by damage to the mitochondria in the cells
    • Mitochondria are responsible for producing energy or ATP and as such are the ‘power packs’ of the cell
    • If the cell does not receive enough energy it does not function correctly
    • Symptoms of the disease vary and is dependent on the number and location of cells that are damaged
    • The most common part of the body that is affected are usually those with the highest demand for energy such as the brain, muscles, liver, heart and kidneys
    • They are rare, very hard to distinguish and is currently no treatments available

     

    The Gillard family – background
    • Jean Gillard suffers from mitochondrial disease, an inherited condition passed down maternally – i.e. from the mother
    • Although it is too late for her family, the success of genetic egg transplants in genetically modified monkeys in America could eliminate genetic diseases

     

    PGD and the creation of a tissue matched sibling – the Whitakers

    • Video ‘Couple welcome MPs’ vote’ – BBC News, 20th May 2008 (3min10)

     

    What is a ‘Saviour Sibling’?
    • The term ‘Saviour Sibling’ is used to describe a child who is born to provide stem cells or organ transplants to a sibling who suffers from a disease.

     

    Who are the Whitaker family?
    • Charlie Whitaker suffered from Diamond Blackfan Anaemia (DBA) 
    • The best possible chance for Charlie to live a relatively normal life was to perform a transplant from a tissue-matched donor
    • The family wished to screen their embryos to select a tissue match for Charlie. At the time, however the HFEA would not allow the procedure as they believed that there would be no benefit and potential harm for the new child
    • The family therefore travelled to America to carry out the procedure – they became an early example of the phenomenon known as ‘fertility tourism’
    • As a result, Jamie was born – a tissue type match for Charlie
    • Stem cells were harvested from Jamie’s umbilical cord and successfully used in a bone marrow transplant for Charlie

     

    What is Diamond Blackfan Anaemia?
    • A disorder that gives a low red blood cell count
    • Usually treated with corticosteroids and blood transfusions
    • Bone marrow transplants 
    • Thought to be spontaneous rather than an inherited condition
    • It is characterized by genetic heterogeneity where by a number of different genes may be involved 
    • Currently impossible to screen embryos for the disease

     

    What is the current law surrounding tissue matched siblings?
    • UK law currently allows PGD for tissue-matched siblings on a case by case basis
    • Some of the criteria includes whether the condition is life threatening
    • Only cord blood should be used to decrease any suffering for the donor baby
    • However, PGD procedures are still allowed in other countries, and as such, fertility tourism is still likely to occur 

     

    Are there any other cases where PGD for tissue matched sibling has been allowed in the UK?
    • Zain Hashmi suffers from thalassaemia – an inherited blood disorder
    • The HFEA initially gave permission to Zain’s family to produce a saviour sibling
    • After pro-life campaigners sought to ban the treatment, the case was taken to the High Court who found in favour of the family
    • The HFEA argued that the procedure would benefit both Zain and the new child
    • As of yet however the Hashmi family have been unsuccessful in producing a suitable donor embryo

     

    PGD for diagnosing late onset diseases – Breast Cancer

    • Some diseases do not develop until much later in life 
    • They include Alzheimer’s, Huntington’s, heart disease and some cancers
    • Complex situation as they have both genetic and environmental influences
    • Genetic tests can show whether a person may be susceptible to these diseases

     

    Breast Cancer
    • 40,000 cases of breast cancer are diagnosed every year in the UK
    • 5-10% are thought to be caused by a mutation in the ‘breast cancer genes’ BRCA1 and BRCA2
    • The risks of getting breast cancer increase with age and as such is a sporadic disease (i.e. a genetic disease that occurs without any family history or genetic defects from the parents – not inherited)

     

    The use of PGD and breast cancer
    • Carrying the breast cancer genes alone does not guarantee that cancer may develop
    • In these cases, the disease is said to have ‘incomplete penetrance’ and as such the use of PGD is questioned
    • First allowed by the HFEA in May 2007 to screen embryos for genes such as BRCA1 but is still permitted on a case by case basis

     

    Background to the video
    • The story relates to a baby who has been born who was the first to be screened for an altered gene which causes breast cancer
    • Women in three generations of her husband’s family have been diagnosed with breast cancer in their 20s
    • The couple, a 27 year old and her husband, were treated by fertility expert Paul Serhal at University College Hospital London
    • Wished to remain anonymous
    • A daughter could have been affected by breast cancer herself if she carried the altered gene and a son could have been  a carrier and passed it to any daughter he may have
    • Mr Serhal, ‘The objective of this exercise is not just to make sure the child doesn’t have the gene but to stop the transmission from generation to generation.’
    • However, not carrying an altered BRCA1 gene would not guarantee any daughter born to the couple would be unaffected by breast cancer because of other genetic and environmental causes

     

    Ethics

    What are the ethical benefits of PGD?
    • Eliminate genetic disorders
    • Allow ‘tissue match’ with older siblings in order to donate stem cells to cure another sibling
    • Strongest supporters of PGD are characteristically libertarians who believe we should have the freedom to make one’s own reproductive choices

     

    What are some ethical concerns of PGD?
    • Alters the relationship between parents and child so a ‘gift’ becomes a ‘commodity’
    • Fate of the embryos that are not selected 
          • Some believe that life begins at conception and so it is viewed that destroying rejected embryos is morally wrong
    • ‘Deselecting’ embryos that may have genetic disabilities is sometimes seen as taking a huge slur on individuals who already live with such conditions
          • It is argued that it is society’s attitude to disability rather than the life of a ‘handicapped’ individual which needs to be rejected
    • Eugenics 
          • Arguments against PGF have been raised over the idea of eugenics, that it is the attempt to influence the genetics of the population by controlling reproduction
    • Psychological concerns for the saviour sibling
          • How would they feel, knowing they were only produced to save another?
          • How would they feel if the treatment failed?
          • The donor sibling may have to go through more suffering if further procedures e.g. bone marrow transplant, were required
    • Financial arguments
          • IVF and PGD are very expensive, several thousand pounds per cycle
          • Issues of justice and fairness
          • NHS resources are limited
          • Permission given to one family may cause another to lose out on this treatment
     
     
     

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