HIRA and alpha thalassemia-X-linked intellectual disability syndrome: The replacement of H3.1 with H3.3 takes place after DNA replication and relies on the histone chaperones HIRA (histone cell cycle regulator), which functions broadly during interphase of cell division, and the Arabidopsis thaliana ATRX (Alpha-Thalassemia X-Linked Intellectual Disability Syndrome) protein ortholog, which functions only for a short period before mitosis [38,39].