The currently established genetic causes of male infertility comprise abnormalities on all genomic levels from chromosomal abnormalities, in particular Klinefelter syndrome, to Y-chromosomal (azoospermia factor, AZF) deletions, to mutations of the cystic fibrosis transmembrane conductance regulator (CFTR, all gene information - name, location, IDs - available as Table S1) gene. This evidence concerns the gene CFTR and Klinefelter syndrome.