HES1 and Azoospermia: Male gonad tissue samples collected from patients with NOA harbouring a mutation in the TKTL1 gene showed a significant downregulation in HERC5, CSF3, HES1 and HSPA1B genes, compared with patients with azoospermia without mutation in the TKTL1 gene (negative control) as well as control samples with normal spermatogenesis.