Previously we have shown that the severity of α-thalassaemia in ATR-X syndrome is determined, to a large extent, (accounting for ~60% of the variance) by the length of a G-rich variable number tandem repeat (ψζ) lying upstream of the α-globin cluster to which ATRX binds. Here, ATRX is linked to Alpha-thalassemia - X-linked intellectual disability syndrome.