Infertile

Question

I have two sons. We recently found out that they both have a mild form of CF. They have never been ill. My eldest son wanted children and now it seems as if he doesn’t have semen in his body. Also operatively it was impossible to obtain sperm cells. He will thus never have a child of his own.
In the other son there is also no living sperm cells in his ejaculate. At present he doesn’t have a steady relationship and there has been no further testing because that would be very invasive. He had surgery several times because he had an accident. Is the chance that he is totally infertile equal for him or can’t you state it like that?

Answer

The disease CF develops when 2 changes (mutations) in the CFTR gene are present. The CFTR gene is a big piece of hereditary material (DNA) responsible for the development of the disease. In the normal situation a normal CFTR protein is made that functions as a chloride channel at the surface of the cells. In persons with a mutation on each of the CFTR genes less CFTR protein is formed. This protein is necessary for development of amongst others the male reproductive organs. The male reproductive organ is very sensitive to changes in CFTR protein and is therefore usually damaged in milder forms of CF. Secondary to this there is infertility.

The decreased amount of CFTR protein causes in men with CF an obstruction or absence of the vas deferens also called congenital bilateral absence of the vas deference (CBAVD). 97% of men with CF have absence of the vas deferens and also the seminal vesicles can be absent. Apart from abnormalities in the formation of these organs, abnormalities in development and maturation of the sperm cells have been found in CF men. The sperm cells can be malformed or can be immotile.
Different types of mutations are known in CF and can lead to different functional amounts of CFTR protein. Depending on the amount of CFTR that remains present you have milder or more severe forms of CF.

Of course we don’t have data on your sons. Therefore we can only speak in general terms.
If brothers are found to have a mild form of CF it is indeed expected that they both carry the same mutations. Both then have the same risk of CF since 97% of the men with CF have CBAVD. Whether a brother with CF who has not been tested has no sperm at all it is difficult to predict. Between brothers there can be some variability in the amount of protein that is still being formed. Mainly because the function of the CFTR protein can be influenced by other genetic factures apart from the CFTR gene. In rare cases it has been reported that although brothers carry the same mutations genetically the one brother is fertile and the other is not (Mercier et al 1995). We thus can’t predict if a brother with the same genes will also have no functional sperm cells.
Dr. I. Bronsveld

15.11.2010