Genetic Diseases

Objectives To recap genetic inheritance To identify four genetic diseases To review key factors to study To propose research

The gametes (sex cells of humans each contain 23 chromosomes. This is half the number of all other cells.

When the sperm meets

the egg their nuclei fuse giving 23 pairs (46) chromosomes. The number present in all of our cell nuclei (except our sperm and eggs)

Reproduction:

Features Many of our features

are controlled by the genes on our chromosomes.

This is why we often look like our parents.

But we don’t always. We will discuss the

reasons.

Important termsAlleles: These are alternative types of one gene.

Homozygous: You have the same two alleles for a gene.

Heterozygous: Your two alleles are different

Genotype: The combination of alleles that you have.

Phenotype: The features you actually have. This is a human karyotype – all the

chromosomes laid out. You can see they are in pairs

Other important terms Dominant: You only need one of your two

alleles to be this to see it. It means the phenotype is the same whether you are homozygous (have two dominant alleles) or heterozygous (have one dominant allele) Example Huntington’s disease: you have it if you inherit the allele from one parent

Recessive: you need both of your alleles to be this to see its affects. Your phenotype only shows this if you are homozygous: have two recessive alleles. E.g. Cystic fibrosis and others…….

Albinism

Albinos don’t normally have albino parents. It is a recessive condition and an albino must have two albino alleles.

That means they must have got one albino allele from each parent.

One in every 130 individuals carries the gene for albinism but the condition is much less common because both parents must be carriers and the child must inherit the albino allele from both (a 1 in 4 chance).

One child in every 17000 is albino.

What is a genetic disease?

1• Many diseases have a genetic component

including breast cancer and diabetes 1 and 2

2• Some diseases are the result of one faulty

gene like albinism. Often they are fatal!

3• The faulty gene may be dominant or

recessive

Example Cystic Fibrosis Also known as mucoviscidosis (sticky mucus) Developmental disease Lungs do not develop properly Digestive system does not absorb food Pancreas stops functioning Observed in infancy Untreated leads to very early death Treated increases survival but likely to reduce

growth Some people seem very healthy Others seriously compromised

Complications Many respiratory infections Poor growth due to malnutrition Diabetes due to damage to pancreas Intestinal blockage in newborns Sterility due to blockage of sperm duct

(sperms fine) Cirrhosis of the liver

Inheritance This is a recessive disease This means you must have both alleles

to have the disease; If you have one allele you are a carrier

and do not show the disease; Both parents must be carriers for a child

to have a disease Chance of having disease is 1 in 4

Pathology CF is caused by a mutation in the gene

for the protein cystic fibrosis transmembrane conductance regulator (CFTR);

This protein regulates the components of digestive juices, sweat and mucus;

Only one healthy gene is needed for this to function

Genetics There are over 1500 possible mutations

to the CFTR gene that can lead to CF Over 60% of cases worldwide are due to

one specific mutation; Screening usually tests for up to 32

different mutations, but this does mean that some cases can be missed by screening.

Prevalence Commonest in western European

Caucasians (1 in 25 are carriers) Highest prevalence in Ireland Non European populations much rarer and

usually a different mutation (1 in 46 Hispanics in US, 1 in 65 African Americans)

In 1959 median age of survival was 6 months

The median survival age in Canada has increased from 24 in 1982 to 47.7 in 2007

Treatment and cure Possible cure through introduction of gene to

airways – early stages Treatment of lung diseases through antibiotics Preventative use of antibiotics Physiotherapy to help clear lungs of fluid Replacement of digestive enzymes (pills) Insulin Healthy diet and exercise May need lung, liver and pancreas transplants Assisted reproduction

Prevention At risk adults may get genetic testing. Expensive so usually only one parent done at first

(many mutations screened for) Pre-implantation genetic diagnosis Testing of foetus in utero by amniocentesis or

chorionic villus sampling of placenta Screening of new born: test sweat Parents may notice baby tastes salty Worst option wait till respiratory complications and

poor growth show; Best prognosis with earliest diagnosis

Amnioscentesis Carries a risk of about 1 in 200 of initiating an abortion

Ethics What ethical issues surround the

following decisions 1. To start a family 2. To test foetuses 3. To decide against having a child 4. Gene testing and medical records

Investigation

1.• Produce an investigation into another

genetic disease

2.• Follow the structure I have used for cystic

fibrosis

3.• Investigate in depth research into treatment

including such approaches as gene therapy.

Themes

• Huntington´s DiseaseTeam 1• Sickle Cell AnaemiaTeam 2• HaemophiliaTeam 3• Severe Combined

ImmunodeficiencyTeam 4

Rubric 1 mark = a relevant piece of info 2 marks = several relevant pieces of

info 3 marks = most relevant info there 4 marks = Comprehensive information

clearly expalined. Ten content areas: 4 marks per area,

total out of 40.

Content areas

1.

• General information and facts

2.• Medical Complications

3.• How it is inherited

4.• Inheritance diagram

5.• Pathology

6.• Genetics

7.• Prevalence

8.• Treatment and Cure

9.• Prevention

10.

• Modern research