Approximately 1% of all men do not produce sufficient amount of sperm, and the genetic basis of the majority of cases is unknown. In two unrelated consanguineous families we first found the chromosomal locations of the defective genes responsible for azoospermia and later identified gene defects in TAF4B and ZMYND15. We screened 60 unrelated azoospermic men but did not find any mutations in those genes. These first genes for recessive idiopathic azoospermia are likely not responsible for an important fraction of male sterility, and possibly hundreds of genes work together in sperm production in men, as in mice.  (By Professor Aslıhan Tolun, http://jmg.bmj.com/content/early/2014/01/15/jmedgenet-2013-102102 )