IQUB and Azoospermia: Within the subset of cases with a genetic etiology, mutations in specific IQ motif genes have been established as monogenic causes for distinct phenotypes: IQUB (c.942T > G) with asthenozoospermia, IQCN (c.1061_1062delAT) with total fertilization failure, and IQCH variants with azoospermia (5, 7, 16).