Skip main navigation

Case Study 1: Some introductory information

What is Cystic Fibrosis and how is it inherited?
colourful modern pixelated-like image of the lungs representing Cystic fibrosis
© Wellcome Genome Campus Advanced Courses and Scientific Conferences

This first story is about an inherited condition called Cystic Fibrosis.

CF is caused by altered CFTR genes. The CFTR protein controls the movement of salt and water in and out of cells. People with CF experience a build-up of thick, sticky mucus in the lungs, digestive system and other organs, causing a wide range of challenging symptoms affecting the entire body.

This condition is inherited in an autosomal recessive pattern (see Glossary). Genetic counsellors do risk calculations to figure out the chances of a couple having an affected child. We will walk you through the risk calculation we would do in this case.

To work out the risks of a couple having an affected pregnancy you first need to work out the chance that each parent is a carrier of CF.

Ths chance Genevieve is a carrier is 1 in 2 (also written as 1/2). We know this because of her family history. The chance Sam is a carrier is 1 in 25 (1/25). This is the population risk for people with white northern European heritage.

You then multiply these figures together. This gives you the probability that both parents are carriers. This chance is 1 in 50 (1/50).

This figure is then multiplied by 1 in 4. This is the chance that, if parents are carriers, they will both pass on a copy of the gene with a disease-causing alteration.

If one parent is affected with CF (has two copies of CFTR with an alteration) then the risk calculation is different. This can be complicated as there are mild forms of CF. In some rare cases people will not be affected until they are adults. For this calculation, and our purposes here, we are thinking about ‘classic’ CF. This presents in childhood.

For a further exploration of recessive inheritance you might like to watch the following video.

https://vimeo.com/album/5216273/video/273660858

© Wellcome Genome Campus Advanced Courses and Scientific Conferences
This article is from the free online

What is Genetic Counselling?

Created by
FutureLearn - Learning For Life

Our purpose is to transform access to education.

We offer a diverse selection of courses from leading universities and cultural institutions from around the world. These are delivered one step at a time, and are accessible on mobile, tablet and desktop, so you can fit learning around your life.

We believe learning should be an enjoyable, social experience, so our courses offer the opportunity to discuss what you’re learning with others as you go, helping you make fresh discoveries and form new ideas.
You can unlock new opportunities with unlimited access to hundreds of online short courses for a year by subscribing to our Unlimited package. Build your knowledge with top universities and organisations.

Learn more about how FutureLearn is transforming access to education