CLPP and Infertility: Non-obstructive azoospermia (NOS, the complete absence of sperm from the ejaculate, due to a failure in spermatogenesis, leading to complete infertility) was observed so far in one of the few male individuals with a biallelic missense mutation in the gene encoding the mitochondrial matrix peptidase CLPP, and in all mice with a genetic depletion of this protein [1,2,3].