Cystic Fibrosis?
Wednesday, August 25th, 2010 at
7:42 pm
gixxeracer87 asked:
Assume that you have a brother or sister with CF and that you and a Caucasian partner who has no family history of CF have a child. What is the likelihood of your child being affected?
Tagged with: Brother • Cf • Likelihood
Filed under: Cystic Fibrosis
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Well, that’s hard to say. I’m not positive about CF’s inheritance but as long as it’s like most other basic genetics, this should be correct.
Because there’s no mention of the parents having it, I have to assume they were not affected by it and only carried the recessive gene. So they each carry one dominant normal gene (let’s call that ‘N’) and one CF gene, which is recessive(let’s call this one ‘a’). You would need both recessives to show signs of the trait, but can carry it either way. Because one of the two genes will come from each person, if either one happens to have two dominant genes, there is no probability that there will be a problem.
Alrighty, now it’s all probability. Since I am not affected, I have to assume that I have at least one N. Best case, I have 2 Ns and there is no possibility of the child having it. Now, worst case, I have one N and one a.
The next big problem is that it is (to my knowledge) impossible to tell whether or not my partner has the recessive gene because as long as the N is there. So, best case, my partner has 2 N and there’s no problem. Worst case, he has a recessive so he, also, has N and an a.
If both have N & a then we go into all the possible combinations NN, Na, aN, and aa. Only aa has no Normal one to override the faulty programming of the ‘a’. Therefore, there is a 25% chance, in that instance.
That is, to the best of my knowledge, the answer to your very very complicated question. However, I’d have to say that a doctor or a CF specialist would know far more then my Biology classes have taught me because they know how CF is passed down. My answer is only educated conjecture.
If you are the person with the family history of CF but don’t have the disease yourself you may or may not be a gene carrier. You and your partner should be tested for the CF gene. Even though your parner’s family doesn’t have a family history of it the gene may still be there but the right combination just hasn’t ever occurred for there to be a case of CF. Since CF is a recessive gene it will skip generations and will even affect children from the same parents differently.
If you draw out the gene mapping for two CF carrier parents, one child will not have CF, one will have the disease and two will be carriers. Of course real life never occurs quite as neatly as the mapping process.
I’m a 40 year old CF’er and was the first family member on my dad’s side of the family to ever be diagnosed with CF. One of my 2nd cousins also had the disease, although he was born after me. We now know of several family members on that side that are carriers, due to the testing, but there are currently no other CF cases. I had a great uncle that died while a toddler after a history of pneumonia, generally being ‘sickly’ etc. and it’s strongly suspected that he had CF but he was born prior to CF being ‘discovered’.
On my mom’s side I am the only CF’er and there is no family history of it, either proven or assumed. Several of my cousins have been tested and they are carriers.
If you and your partner are tested and are fortunate to find that neither of you, or only one of you, are carriers then you can have children without having to worry about them having CF. Should you find that one of you is a carrier your child still will not have CF but you will need to be sure the child is tested for the gene at an early enough age that he/she knows the potential for their own children to have CF.
Having CF is not the worst thing in the world. Granted any of us that have it would love to not have it, but there are many other diseases that I personally think would be far worse to have. I’ve been very fortunate, however, to have top quality care since birth and have mostly been able to live my life on my own terms. I was blessed with a double lung transplant 3 years ago when the CF had progressed to the point that was the only option for treatment. Now the disease is cured in my lungs – amazing what freely breathing is! – but there are a number of other aspects of the disease that I will always have, in addition to side effects from the transplant.
You need to talk to your family doctor about the CF history in your family and get tested as quickly as possible. Usually testing is done on the mother first and then the father is only tested if the mother is a carrier. However, if you are the father in this case with the known family history they will likely test both of you at the same time.