PTPRN and female infertility: However, because PTPRN is expressed in several other neuroendocrine tissues, other studies have shown that double knock-out of PTPRN and homologue PTPRN2 (IA2-β) causes female infertility due to a reduction in pituitary DCVs and subsequent lowering of serum luteinizing hormone levels, as well as anxiogenic behavior and learning deficits associated with a decrease of norepinephrine, dopamine and serotonin in the brain [65].