In recent years dna diagnosis has become a rapidly developing field: more and more syndromes are being shown to be genetically deter­mined and in a number of diseases it has become clear that a small part of the chromosome, the gene, is not functioning properly. An example of this is cystic fibrosis, a genetic disorder affecting a gene of chromo­some number seven. This poorly functioning gene causes thick sticky mucus in, for example, the airways and the pituitary gland. Blockages of these organs lead to chronic airway infections and growth problems. In many cases the epididymides, the seminal duct and the seminal glands are affected by this ailment. Because sperms are actually being produced in the testicles it is sometimes possible for a sufferer of cystic fibrosis and his partner to achieve a pregnancy through icsi, though a child fathered in this way risks developing a form of cystic fibrosis. For this reason examination of the man and if necessary of the woman is necessary prior to such treatment.

Recently the gene important in sperm production, the azf gene, was found in the male chromosome. Minor writing errors in the order of the dna molecules lead to disruptions in sperm cell production. Mutations in the azf gene are found in between 5 and 15 per cent of all men with poor sperm quality. In the event of successful assisted reproduction these will be passed on to male descendants. This is yet another reason in cases of very poor sperm quality to consult a clinical geneticist.