2: Cystic Fibrosis + inheritance

Question 1

Explain the difference between a dominant and a recessive mode of inheritance in monogenic diseases

Answer 1

In a dominant mode of inheritance, only 1 defective allele is required to result in the disease phenotype
therefore affected person’s genotype may be homozygous or heterozygous for the affected gene

In a recessive mode of inheritance, the affected person needs to have both defective alleles to result in the disease phenotype, therefore the disease only appears in the homozygous state

Question 2

2. What protein does the CFTR gene code for? What is the function of this protein?

Answer 2

The CFTR gene codes for the cystic fibrosis transmembrane conductance regulator

It is a chloride ion channel regulator

Question 3

Explain how the R117H mutation leads to the symptoms of cystic fibrosis?

Answer 3

This mutation leads to a structural change in the channel that conducts chloride within epithelial membranes

• This leads to a reduced capacity to conduct chloride through the channel
• As less chloride flows into the lumen, there is less sodium follows and also less water
• The reduction in water means the mucus on the luminal side is thicker and flows less, leading to the different symptoms associated with cystic fibrosis

Question 4

Describe 3 roles undertaken by a genetic counsellor

Answer 4

• to help calculate the risk that parents having a family history of certain genetic traits might pass on disease traits to their children
• to provide advice on genetic testing and analyze and explain genetic results

to direct clients to other services within the NHS as required

Question 5

what are the symptoms of cystic fibrosis

Answer 5

Symptoms of cystic fibrosis include: recurring chest infections. wheezing, coughing, shortness of breath and damage to the airways (bronchiectasis) difficulty putting on weight and growing.