Which of the following is a true statement regarding G6PD?

a. The gene is located on chromosome 22.
b. The gene has the greatest degree of variability in the human genome.
c. The deficiency is primarily expressed as a clinical disease in heterozygous female subjects.
d. The normal enzyme is called G6PD A.

ANS: B
The G6PD gene has the greatest degree of variability in the human genome; this results in multiple clinical variants. The gene is found on the X chromosome, so it is only rarely clinically expressed in heterozygous female subjects who have one normal X chromosome. However, they can be shown to have varying numbers of G6PD-deficient red cells. The normal enzyme is called G6PD B. G6PD A contains one mutation so that its electrophoretic pattern is different, but it is a benign change.