For example, deletion of SPINK2, an azoospermia-associated gene, caused oligo-teratozoospermia in mice (30), and knockout of Wdr63, a gene mutated in both multiple morphological abnormalities of the sperm flagella and NOA patients, led to infertility with decreased sperm number and abnormal flagellar morphology in mice (31). Here, SPINK2 is linked to Azoospermia.