As more and more people are struggling to get pregnant - according to the WHO, up to 25% of all couples trying to have a baby may have this type of disorder - scientists are constantly looking for possible causes. While factors responsible for infertility in women may be different, others lead to this problem in men. An interesting light is shed on the problem of male infertility by a study conducted by specialists from several centres, published in the journal Proceedings of the National Academy of Sciences.