7.6 Epidemiological studies – Further questions and answers
Q1.
Bk Ch7 S7.6 FQ1
Find out how techniques such as amniocentesis and chorionic villus sampling are used to determine
genetic abnormalities in the developing foetus. What is involved in each technique? Outline any risks
associated with these procedures. List some of the conditions that can be identified using these
technologies.
A1.
Bk Ch7 S7.6 FA1
Amniocentesis is a technique that involves the removal of foetal cells from the amniotic sac in which
the developing foetus is contained. These cells are then examined using a microscope. This method is
used to determine whether or not any chromosomal abnormalities are present. Down syndrome can be
diagnosed using amniocentesis because it shows the presence of an extra number 21 chromosome. The
sex of the foetus is also evident using this method. Amniocentesis increases the risk of miscarriage. It is
usually performed on older women, who have an increased risk of carrying a child with Down
syndrome. It may be performed on younger women who have been identified as having an increased
risk of some chromosomal diseases.
Chorionic villus sampling is a technique that removes foetal cells from the outer membrane of the sac surrounding the foetus. Cells are examined for chromosomal abnormalities such as those evident in
Down syndrome. The advantage of this technique over amniocentesis is that it can be performed earlier
in a pregnancy; however, there is also an increased risk of miscarriage.
Q2.
Bk Ch7 S7.6 FQ2
At the present time, we cannot cure inherited diseases.
a Explain why this is so.
b Describe how genetic engineering techniques might help overcome inherited diseases in the future. c What is gene therapy? How can it be used to treat some inherited diseases? Use an example in
your answer.
A2.
Bk Ch7 S7.6 FA2
a Inherited diseases are genetic in nature. With the exception of eggs and sperm every cell of an
individual’s body has the same complete genome. This means that every single cell also contains
the defective gene causing an inherited disease. To cure an inherited disease we need to correct
the defective gene in all of the body cells.
b Genetic engineering may be beneficial to couples planning a family but who have a history of a
particular genetic disease in one or both families. Eggs and sperm may be harvested using IVF
technology, genetically altered to correct the defect, and then allowed to unite in fertilisation
before being implanted. Similarly, a fertilised egg that is at risk or known to have a genetic defect
could be genetically altered before being implanted. This technique can also be applied to
embryos at very early stages of development, usually less than the eight-cell stage. Current gene
therapy techniques applied to an undifferentiated embryo could also be useful in correcting
genetic defects.
c Gene therapy is the technique of treating patients with otherwise untreatable inherited diseases
with genetically engineered cells or modified DNA. This involves the insertion of non-defective
genes into a target tissue of the patient with the aim of replacing defective genes that are causing
the disease in question. Example: Cystic fibrosis (CF) is an inherited disease resulting from a
single defective gene. One feature of the disease is the presence of excessive mucus in the
respiratory tract that makes breathing difficult. If the normal CF gene is isolated from human
DNA and then inserted into an attenuated virus such as the cold virus it can be applied to the
lungs of a sufferer where in theory it should enter the epithelial cells of the patient. Having
entered the human epithelial cells the inserted gene would function normally, the volume of
mucus in the respiratory passages would be reduced and the patient would breathe more easily.
Q3.
Bk Ch7 S7.6 FQ3 7.6 Epidemiological studies FQA page 1 of 4
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Do some library or Internet research to find out about one of the following diseases.
asbestosis mesothelioma asthma lung cancer emphysema coronary heart disease diabetes
In each case:
? describe the symptoms of the disease
? outline any long-term effects
? describe current treatments and prognoses
? summarise any apparent relationships between the disease and a causal factor indicated by
statistics (include relevant statistics).
A3.
Bk Ch7 S7.6 FA3 Example (mesothelioma):
Mesothelioma is caused by exposure to asbestos. It is characterised by the appearance of a malignant
tumour on the pleura, which is the lining of the lungs and chest cavity. Mesothelioma develops slowly
and is usually diagnosed between 20 and 40 years after exposure, at which time the disease has already
progressed so far as to signal imminent death. The symptoms include shortness of breath, coughing,
chest pain, excessive sweating and weight loss. When diagnosed the mesothelioma tumour can be
treated with radiation therapy or chemotherapy but this is usually unsuccessful. About 75% of patients
die within 12 months of diagnosis. Statistics indicate a clear relationship between exposure to asbestos
and the development of mesothelioma. There is no other known cause.
Q4.
Bk Ch7 S7.6 FQ4 Nuclear power stations are becoming increasingly common for generating electricity for domestic and
industrial use around the world. But nuclear accidents involving dangerous releases of radiation, such
as the accident in Japan in September 1999, are all too common.
a What is radiation sickness? Describe its symptoms, treatment and prognosis.
b What do epidemiological studies suggest about the long-term effects of exposure to high levels of
radiation? Information related to the Three Mile Island incident and the Chernobyl disaster of
1986 may be useful.
A4.
Bk Ch7 S7.6 FA4 a Radiation sickness is the name given to a set of injuries or symptoms suffered by people who
have had excessive exposure to radiation. Immediate symptoms include skin burns with blistering,
nausea, vomiting, diarrhoea and fatigue; delayed symptoms include hair loss and inflammation of
the mouth and throat. First aid measures involve removing the patient from the source of the
radiation and washing the skin thoroughly with soap and water. Some of the symptoms of
radiation sickness can be treated, but there is no treatment for the radiation itself. Depending on
the dose received patients may die within two to four weeks of exposure. If patients survive this
critical period they may eventually recover.
b Long-term effects of excessive exposure to radiation such as that encountered at Chernobyl in
1986 include the unusually high rate of cancer development. Cancers typical of high radiation
exposure include leukaemia and thyroid cancer (associated with the release of radioactive iodine).
Q5.
Bk Ch7 S7.6 FQ5 Use reference books to help you complete the following table, summarising aspects of deficiency
disease in humans.
Disease Cause Symptoms Treatment
Kwashiorkor
Anaemia Scurvy Beri-beri 7.6 Epidemiological studies FQA page 2 of 4
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Pellagra Cretinism Marasmus Rickets Obesity Anorexia nervosa Bulimia Starvation
A5.
Bk Ch7 S7.6 FA5
Disease Cause Symptoms Treatment Kwashiorkor Protein deficiency in Lethargy, weight loss, Inclusion of protein in diet
diarrhoea, dry skin, brittle infants after weaning
hair, oedema
Anaemia Iron deficiency Lack of energy, lethargy, Increase iron intake—red
meats, eggs, liver, lentils, pallor
wholemeal cereals Scurvy Vitamin C (ascorbic acid) Swollen, tender gums; Increase vitamin C
intake—fresh fruits and deficiency susceptibility to bruising
vegetables, especially
citrus fruits Beri-beri Vitamin B (thiamin) Numbness in hands and Increased vitamin B 11feet, damage to nerves, intake—wholegrain deficiency
cereals, lean pork, liver, impaired heart function
beans, peas, peanuts Pellagra Niacin (B group vitamin) Fatigue, headache, Increased niacin intake—
weight loss, loss of meat, poultry, fish, deficiency
appetite, poor general peanuts
health, tender tongue,
sore mouth and throat,
redness of tongue and
lips, dermatitis, nausea
and vomiting, confusion,
dizziness, impaired
memory, general
irritability
Cretinism Iodine deficiency during Mental retardation, Treatment with thyroid
impaired growth and poor hormone can improve foetal development
development but damage development
already sustained is
irreversible Marasmus Deficiency of both protein Lethargy, severe weight Increased protein and
and kilojoules in very loss, failure to grow, kilojoule intake
impaired mental young infants
development
Rickets Vitamin D (calciferol) Poor bone growth, Increased vitamin D
curvature of the long intake—milk, egg yolk, deficiency
fish and liver oils; the bones in the legs
body also manufactures
vitamin D when exposed 7.6 Epidemiological studies FQA page 3 of 4
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to sunlight Obesity Excessive kilojoule intake Overweight; associated Balanced diet with
disorders of the heart, adequate kilojoule intake
weight-bearing joints and regular exercise Anorexia Psychological basis Weight loss, absence of Increased kilojoule intake
manifested by extreme menstruation in females, associated with nervosa
fear of eating, skewed counselling to remedy weight loss
perception of own body underlying psychological
shape problems Bulimia Psychological basis Episodes of binge-eating Counselling and
followed by induced reassurance; may require
vomiting; fatigue, hospitalisation
depression, abnormal
eating patterns,
indigestion, urinary tract
infections, constipation,
irregular menstruation,
heart irregularities
Starvation Diet inadequate in the Weight loss, emaciation, Slowly increase food and
extreme with severely lethargy, nausea, kilojoule intake,
reduced food and maintaining balance of headache, diarrhoea
kilojoule intake food groups
7.6 Epidemiological studies FQA page 4 of 4
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