However, despite widespread usage of karyotyping, azoospermia factor (AZF) deletion screening and cystic fibrosis transmembrane conductance regulator (CFTR) mutation analysis, a recent study in a large unselected patient cohort revealed a causal genetic diagnosis in only 4% of infertile men (Tüttelmann et al. 2018). This evidence concerns the gene CFTR and Infertility.