Whereas H3.3 is specifically deposited into active regions of the genome by the chaperone histone regulator A (HIRA), the complex containing the chromatin remodeler alpha thalassemia/mental retardation syndrome X-linked (ATRX) and the chaperone death domain-associated protein (DAXX) is responsible for H3.3 deposition into heterochromatin [19, 25, 51]. The gene discussed is DAXX; the disease is alpha thalassemia spectrum.