This X-linked disorder is the most common type of haemolytic anaemia due to an intrinsic red cell enzyme defect.
Males who inherit an abnormal gene are invariably affected. Heterozygote females usually have approximately 50% G6PD enzyme activity; the random Lyonisation of X chromosomes means that rarely carrier females may be severely affected.
It is most common in the Mediterranean, the Middle East, South East Asia and West Africa. It is rare among Caucasians.