Case Study 1: Some introductory information
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). To work out the risks of a couple having an affected pregnancy you make the following calculation:
First, you take the Mother’s Risk multiplied by the Father’s Risk. This gives you the probability that both parents are carriers.
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.
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