The vas deferens are the tubes that carry the sperm from the testicle and epididymis up to the prostatic urethra. Some men have no sperm in their semen because the sperm transport is blocked because the vas deferens did not develop at all or in part. The vas deferens may not form on one side if there is a missing kidney on that same side but this wont cause male infertility as long as there is a normal vas deferens on the other side. If the vas deferens is missing or abnormal on both sides then no sperm will be in the semen. This condition, known commonly as congenital bilateral absence of the vas deferens CBAVD is due to the same gene abnormality that causes cystic fibrosis, a severe disease of the lungs and pancreas that used to mean a death sentence to anyone with it by their young adult hood. Advances in medicine has enabled people with cystic fibrosis are able to live much longer with the aid of newer therapies. The gene that causes cystic fibrosis, known as the cystic fibrosis Tran membrane conductance regulator is on chromosome number 7. It can exist in a large variety of mutations. Some of these mutations are mild in that they only result in an effect on the vas deferens, while other mutations cause the full-blown disease. This gene is recessive, which means the man with the condition must have an abnormal version from both his mother and his father to have the physical effect of the genes. The test for this gene is ordered when the specialist is unable to feel vas deferens on a patient with normal feeling testicles but no sperm in the semen. The treatment for this condition is sperm retrieval surgery and in-vitro fertility ICSI. Many women will carry this gene even though they don’t have cystic fibrosis. Remember, it is a recessive gene which means if a person has only one copy of it-from either his mother or his father, it will not cause any physical effects. If a man has the condition then both of his copies are affected and if he is enabled to father a child but the woman has one copy from one of her parents then there is a one out of 2 chance that the child that will be born will have both of its genes affected (the affected one from the father and possibly the affected one from the mother) and possibly that child would have absent vas deferens, or even full blown cystic fibrosis disease. It is important, therefore, that the woman have genetic testing for cystic fibrosis gene mutations so the couple can understand the likelihood of in-vitro fertility ICSI producing an embryo with cystic fibrosis potential. The test for cystic fibrosis has gotten better over the years, able to detect more and more of the many possible alterations of the gene, but it is still imperfect. The test is more reliable at picking up all the know mutations in caucasians than it is in Asians. For any couple dealing with a cystic fibrosis gene mutation diagnosis the best course of action prior to proceeding with in-vitro fertility ICSI is that both the man and the woman undergo genetic testing (a blood test) and then have their results, even if they are negative, reviewed with a qualified genetic counselor who will take the wife’s heritage into consideration when evaluating what the odds are that her “negative “ test is really negative. If a gene is identified in the woman, then preimplantation genetic screening can be performed on the embryos that are produced with in-vitro fertility ICSI and those embryos with the abnormality would not be transferred back to the woman.