When a female inherits a single gene for G6PD deficiency she is often referred to as a carrier. To understand G6PD carriers, we need to understand X chromosome disorders.
G6PD deficiency lives on the X chromosome. Men have one X chromosome, and women have two X chromosomes. Because of this, X linked disorders are usually thought to affect only males. Whereas a woman will usually have a second normal copy of the gene that can often compensate for the altered gene - this is called being "Heterozygous."
The old medical advice was that female carriers may or may not experience symptoms of G6PD deficiency. But in practice, we see that is not the case - there are many symptomatic females. Females can have unequal X-chromosome activation, and the altered gene might express itself more than the normal gene, causing anemia and other symptoms.
Furthermore, because of the high prevalence of G6PD deficiency worldwide, females that have 2 altered genes (homozygous) make up 10% of the people with this disorder. G6PD is the most common enzyme deficiency in the world, affecting over 400 million people.
If you are G6PD deficient, or your child is G6PD deficient, you also need to be tested to verify whether you have it or not, and to determine how severe your deficiency is. This can be done through a 23andme DNA saliva test and a blood test.
But, what if I don’t feel any symptoms?
Hemolytic anemia can occur suddenly in many people, despite lack of prior symptoms. Furthermore, research shows that hemolysis affects the body even at low levels and can cause danger over time. In some people with G6PD deficiency, a small amount of red blood cell destruction occurs all the time - known as “chronic hemolysis”. It is therefore prudent to follow the "avoid lists" for G6PD Deficiency, even if you do not presently have symptoms, in order to protect your body from possible future chronic and/or acute hemolytic anemia.
Rebecca Rhew, J.D.