2.9 Flashcards
People may be referred for genetic counselling if they have been
diagnosed with a genetic condition
Couples may have had a baby with a genetic condition, or they may be planning a pregnancy but are concerned that they may
carry a genetic condition
Usually referred for genetic counselling by their
GP or a hospital consultant
Genetic counsellors are
specially trained professionals who mainly come from a nursing or medical background
Genetic counsellors have a thorough knowledge of
genetic conditions and the impact they can have on a family
Genetic counsellors try to help people
understand the nature of genetic conditions and how it affects an individual
Genetic counsellors can offer advice on whether the
disorder can be prevented, or whether it is possible to diagnose the condition prenatally
The first meeting between a genetic counsellor and a client involves
collecting information about the family history
It is possible that genetic tests need to be carried out on the
client(s) or other family members
These tests would be carried out by a
clinical geneticist
After the tests, genetic counsellors can explain the
information available to the client(s), and help them through associated emotional issues
Genetic counsellors never tell a client what to do, but support them by
discussing issues and making information available
(GENETIC SCREENING) some genetic conditions can be diagnosed b taking a sample of some cells from the person and
extracting their DNA
(GENETIC SCREENING) if the DNA base sequence of the gene causing the genetic disorder is known, the DNA can be examined to see if the individual has a
genetic disorder
(GENETIC SCREENING) It may also be possible to tell whether the person is a
carrier of a disorder
(GENETIC SCREENING) Some genetic conditions may be detected by testing for levels of
specific enzymes (e.g. in blood samples)
(GENETIC SCREENING) One problem with genetic screening is that we cannot
screen for every genetic disorder at the moment
(GENETIC SCREENING) Another problem with genetic screening is that many genetic conditions are caused by several different mutations and we are not able to
screen for every single mutation
(TESTING UNBORN BABIES) It is possible to examine DNA from a foetus by carrying out
amniocentesis or chorionic villus sampling
(TESTING UNBORN BABIES) Amniocentesis can be carried out between how many weeks of pregnancy
15-20
(TESTING UNBORN BABIES) first stage of amniocentesis:
ultrasound is used to locate the position of the foetus
(TESTING UNBORN BABIES) second stage of amniocentesis:
hypodermic needle is inserted through the mother’s abdomen and into the uterus
(TESTING UNBORN BABIES) third stage of amniocentesis:
a small sample of the amniotic fluid, in which the foetus is growing, is removed into a syringe (this fluid will have foetal cells in it)
(TESTING UNBORN BABIES) fourth stage of amniocentesis:
the cells may be cultured so that the foetus’ chromosomes can be examined
(TESTING UNBORN BABIES) alternatively in amniocentesis - the foetus’ DNA can be extracted from the cells and
tested to see if it contains a gene for a genetic disorder
(TESTING UNBORN BABIES) Amniocentesis is not usually performed before 15 weeks of pregnancy because of an
increased risk of causing miscarriage
(TESTING UNBORN BABIES) another diagnostic test is
chorionic villus sampling (CVS)
(TESTING UNBORN BABIES) CVS can be carried out from about
10 weeks of pregnancy
(TESTING UNBORN BABIES) first stage of CVS:
Ultrasound is used to guide a flexible tube (catheter) through the woman’s vagina, through the cervix and close to the placenta
(TESTING UNBORN BABIES) second stage of CVS:
A syringe on the other end of the catheter is used to remove a small amount of tissue from the placenta
(TESTING UNBORN BABIES) CVS is sometimes done using a needle through the
abdomen (as in amniocentesis)
(TESTING UNBORN BABIES) CVS gives a 1-2% chance of miscarriage, which is slightly higher than the risk of miscarriage when
amniocentesis is carried out
(TESTING UNBORN BABIES) If, due to amniocentesis or CVS, a foetus is found to have a genetic disorder, the parents will be offered advice from a
genetic counsellor
(TESTING UNBORN BABIES) as a result of the advice the parents may choose to
terminate the pregnancy
(KARYOTYPING) Cells from a foetus can be cultured in a special medium. This contains a chemical that stimulates the cells to
divide by mitosis
(KARYOTYPING) A spindle inhibitor is used so that many of the cells will start to divide but will not
complete mitosis
(KARYOTYPING) A photograph of the chromosomes is taken and the images
manipulated on a computer screen
(KARYOTYPING) the chromosomes are arranged into their homologous pairs, starting with the largest pair and ending with the smallest. This arrangement is called a
karyotype
(KARYOTYPING) A karyotype like this can detect abnormalities of the chromosomes, but not a
disorder involving a single gene
(KARYOTYPING) Disorders involving individual genes can be detected using
DNA analysis
(EMBRYO SCREENING) If a couple is at risk of having a child with a genetic disorder, such as CF, they may choose to have a baby by
embryo screening
(EMBRYO SCREENING) Involves producing several embryos using IVF treatment - the embryos are allowed to grow to a
4- or 8-cell stage
(EMBRYO SCREENING) At this 4-/8-cell stage, the embryo is held steadily in a suction pipette, while a smaller, sharper pipette breaks open the protein covering of the embryo and
sucks out a single cell
(EMBRYO SCREENING) The DNA from this cell can be extracted and tested to see
whether the alleles causing the disorder (e.g. CF) are present
(EMBRYO SCREENING) Embryos that do not carry the allele for the disorder (e.g. CF) will be implanted into the woman’s uterus. This technique is sometimes called
pre-implantation genetic diagnosis (PGD)
(EMBRYO SCREENING) the DNA from one embryo may be tested for a large number of different
genetic sequences
(EMBRYO SCREENING) The embryo is not harmed, as it has only lost a single cell, however, it is a very new technique so nobody born using this technique is yet old enough to have their own children - therefore we cannot be certain that there is
no long-term harm
(EMBRYO SCREENING) The embryo is also unable to give consent to the
treatment
(EMBRYO SCREENING) Some people are unhappy about PGD because it involves creating a large number of embryos
many of which are not used
(EMBRYO SCREENING) Some people feel that selecting embryos allows couples to have a…
‘designer baby’
(EMBRYO SCREENING) However, embryo testing is regulated by the Human Fertilisation and Embryology Authority (HFEA) and is only allowed for
serious genetic conditions