Which among the following is the commonest enzyme deficiency?

Glucose-6-phosphatase deficiency is the commonest genetically determined enzyme deficiency in the world. G6PD catalyzes the first step of pentose phosphate pathway and is the enzyme controlling the flux through the pathway. It s activity is controlled by the availability of NADP+. In the red cell G6PD determines the reduction of NADP+ to NADPH. NADP+ availability is is determined by the activity of glutathione cycle which is linked to pentose phosphate pathway through the activity of the enzyme glutathione reductase. Availability of NADP+ is the major rate limiting step for pentose phosphate pathway. Ref: Postgraduate Haematology By Anthony R. Green page 149