7.6 Epidemiological Studies Further Questions and Answers

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.

aExplain why this is so.

bDescribe how genetic engineering techniques might help overcome inherited diseases in the future.

cWhat 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

aInherited 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.

bGenetic 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.

cGene 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

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.

aWhat is radiation sickness? Describe its symptoms, treatment and prognosis.

bWhat 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

aRadiation 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.

bLong-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
Pellagra
Cretinism
Marasmus
Rickets
Obesity
Anorexia nervosa
Bulimia
Starvation

A5.

Bk Ch7 S7.6 FA5

Disease / Cause / Symptoms / Treatment
Kwashiorkor / Protein deficiency in infants after weaning / Lethargy, weight loss, diarrhoea, dry skin, brittle hair, oedema / Inclusion of protein in diet
Anaemia / Iron deficiency / Lack of energy, lethargy, pallor / Increase iron intake—red meats, eggs, liver, lentils, wholemeal cereals
Scurvy / Vitamin C (ascorbic acid) deficiency / Swollen, tender gums; susceptibility to bruising / Increase vitamin C intake—fresh fruits and vegetables, especially citrus fruits
Beri-beri / Vitamin B1 (thiamin) deficiency / Numbness in hands and feet, damage to nerves, impaired heart function / Increased vitamin B1 intake—wholegrain cereals, lean pork, liver, beans, peas, peanuts
Pellagra / Niacin (B group vitamin) deficiency / Fatigue, headache, weight loss, loss of appetite, poor general health, tender tongue, sore mouth and throat, redness of tongue and lips, dermatitis, nausea and vomiting, confusion, dizziness, impaired memory, general irritability / Increased niacin intake—meat, poultry, fish, peanuts
Cretinism / Iodine deficiency during foetal development / Mental retardation, impaired growth and poor development / Treatment with thyroid hormone can improve development but damage already sustained is irreversible
Marasmus / Deficiency of both protein and kilojoules in very young infants / Lethargy, severe weight loss, failure to grow, impaired mental development / Increased protein and kilojoule intake
Rickets / Vitamin D (calciferol) deficiency / Poor bone growth, curvature of the long bones in the legs / Increased vitamin D intake—milk, egg yolk, fish and liver oils; the body also manufactures vitamin D when exposed to sunlight
Obesity / Excessive kilojoule intake / Overweight; associated disorders of the heart, weight-bearing joints / Balanced diet with adequate kilojoule intake and regular exercise
Anorexia nervosa / Psychological basis manifested by extreme weight loss / Weight loss, absence of menstruation in females, fear of eating, skewed perception of own body shape / Increased kilojoule intake associated with counselling to remedy underlying psychological problems
Bulimia / Psychological basis / Episodes of binge-eating followed by induced vomiting; fatigue, depression, abnormal eating patterns, indigestion, urinary tract infections, constipation, irregular menstruation, heart irregularities / Counselling and reassurance; may require hospitalisation
Starvation / Diet inadequate in the extreme with severely reduced food and kilojoule intake / Weight loss, emaciation, lethargy, nausea, headache, diarrhoea / Slowly increase food and kilojoule intake, maintaining balance of food groups

7.6 Epidemiological studies FQApage 1 of 4