Expression of the G6PD locus on the human X chromosome is associated with demethylation of three CpG islands within 100 kb of DNA.

We have previously reported that expression of the G6PD locus is correlated with the methylation status of two islands of CpG dinucleotides which are 3′ to the locus and in the 5′ region of two adjacent genes of unknown function, P3 and GdX. We have now examined the methylation of a third CpG island in the promoter region of the G6PD gene itself in DNA from males, females and reactivants that express G6PD on the inactive X chromosome. Our results show that expression of the G6PD gene is associated with concordant demethylation of all three CpG islands in this 100‐kb region of DNA.