G6PD Deficiency: Genetics, Symptoms, and DNA Testing

More than 400 million people carry an enzyme deficiency they may never know about - until the wrong medication, infection, or even the wrong food triggers a crisis that destroys their red blood cells (Nkhoma et al., 2009). It's called glucose-6-phosphate dehydrogenase (G6PD) deficiency, and it's the most common enzyme disorder in humans.

If you have raw DNA data from 23andMe or AncestryDNA, a handful of genetic variants - including rs1050828, rs1050829, and rs5030868 - can reveal whether you carry G6PD deficiency. Here's what the science says, why this deficiency exists in the first place, and what to do if you have it.

What Is G6PD and Why Does It Matter?

Glucose-6-phosphate dehydrogenase (G6PD) is an enzyme found in every cell of your body, but it plays its most critical role inside red blood cells. G6PD catalyzes the first step of the pentose phosphate pathway, producing NADPH - a molecule your cells need to neutralize reactive oxygen species (Cappellini & Fiorelli, 2008).

Think of NADPH as your red blood cells' fire extinguisher. Without it, oxidative stress - from infections, certain drugs, or even fava beans - damages hemoglobin and the cell membrane. The red blood cells literally burst open in a process called hemolysis (Luzzatto et al., 2020).

Most cells in your body can generate NADPH through other pathways. Red blood cells can't - they lack mitochondria and a nucleus, so the pentose phosphate pathway is their only source of NADPH. That makes G6PD absolutely essential for red blood cell survival (Cappellini & Fiorelli, 2008).

How Common Is G6PD Deficiency?

G6PD deficiency affects an estimated 400–500 million people worldwide, making it the most prevalent enzyme deficiency known (Nkhoma et al., 2009). Prevalence varies dramatically by ancestry and geographic region:

• Sub-Saharan Africa: 10–25% of males affected, with the G6PD A- variant being most common (Howes et al., 2012)
• Mediterranean region (Italy, Greece, Turkey, Middle East): 5–30% in some populations, with the G6PD Mediterranean variant predominant (Cappellini & Fiorelli, 2008)
• Southeast Asia: 5–15%, with multiple variants including Mahidol, Viangchan, and Canton (Howes et al., 2012)
• African Americans: approximately 10% of males carry the G6PD A- variant (Chinevere et al., 2006)
• Northern European descent: less than 0.5% (Nkhoma et al., 2009)

Because the G6PD gene sits on the X chromosome, this is an X-linked recessive condition. Males (XY) with one deficient copy are fully affected. Females (XX) with one deficient copy are carriers - but due to X-inactivation, some carrier females can still experience symptoms, especially during oxidative stress (Luzzatto et al., 2020).

Why Does G6PD Deficiency Exist? The Malaria Connection

A genetic variant that destroys red blood cells sounds like it should have been eliminated by natural selection. Instead, G6PD deficiency has been positively selected for over thousands of years - because it provides protection against malaria (Tishkoff et al., 2001).

The parasite Plasmodium falciparum infects red blood cells and relies on their internal machinery to replicate. G6PD-deficient red blood cells, with their reduced antioxidant defenses, create a hostile environment for the parasite. Infected deficient cells are also cleared more rapidly by the spleen (Clark et al., 2009).

This is the same evolutionary tradeoff seen with sickle cell trait - a potentially harmful mutation persists because carriers gain an advantage against malaria. A landmark study published in The Lancet Haematology confirmed that females heterozygous for G6PD deficiency had both less severe malaria and decreased mortality (Uyoga et al., 2015).

The geographic overlap between G6PD deficiency prevalence and historical malaria endemic zones is striking - sub-Saharan Africa, the Mediterranean, the Middle East, and Southeast Asia are all regions where malaria shaped human genetics for millennia (Howes et al., 2012).

The Genetics: Key Variants and WHO Classification

Over 200 genetic variants of the G6PD gene have been identified (Minucci et al., 2012). However, a few common variants account for the vast majority of cases:

• G6PD A- (rs1050828 G>A + rs1050829 A>G): The most common variant worldwide, found primarily in people of African descent. Causes moderate deficiency (10–60% enzyme activity). Hemolytic episodes are usually self-limiting (Cappellini & Fiorelli, 2008).

• G6PD Mediterranean (rs5030868 C>T): Common in Southern European, Middle Eastern, and North African populations. Causes severe deficiency (less than 10% enzyme activity). Associated with more serious hemolytic crises, including favism - hemolysis triggered by eating fava beans (Luzzatto et al., 2020).

• G6PD Mahidol (487G>A): The most common variant in Southeast Asia, particularly Myanmar and Thailand. Moderate deficiency (Howes et al., 2012).

• G6PD Canton (1376G>T): Found primarily in Chinese and Southeast Asian populations. Severe deficiency (Minucci et al., 2012).

In 2022, the World Health Organization revised its classification of G6PD variants, merging the former Class II (severe) and Class III (moderate) into a single Class B category, recognizing that enzyme activity levels overlap significantly between these groups (WHO, 2022). The updated classification is:

• Class A: Severe deficiency with chronic hemolytic anemia (rare)
• Class B: Deficiency with acute hemolytic anemia (most common deficient variants)
• Class C: Mild deficiency (10–60% activity, usually asymptomatic)
• Class U: Unclassified variants with insufficient data

What Triggers a Hemolytic Episode?

Most people with G6PD deficiency are completely asymptomatic - until they encounter a trigger that overwhelms their red blood cells' limited antioxidant defenses. Common triggers include (Youngster et al., 2010; Luzzatto et al., 2020):

Medications to avoid:

• Primaquine and tafenoquine (antimalarials - ironically, the very disease G6PD deficiency protects against)
• Dapsone (used for leprosy and dermatitis herpetiformis)
• Rasburicase (used for tumor lysis syndrome)
• Methylene blue (used as a dye and antidote)
• Nitrofurantoin (antibiotic for urinary tract infections)
• Sulfamethoxazole (the sulfa component in Bactrim/Septra)
• Phenazopyridine (bladder analgesic)

Food triggers:

• Fava beans (broad beans) - particularly dangerous for people with the Mediterranean variant. The compounds vicine and convicine in fava beans generate massive oxidative stress in G6PD-deficient red blood cells (Luzzatto et al., 2020).

Other triggers:

• Severe bacterial or viral infections
• Diabetic ketoacidosis
• Naphthalene (found in mothballs)

Symptoms of a hemolytic episode typically appear 24–72 hours after exposure and include dark-colored urine, jaundice (yellowing of skin and eyes), fatigue, rapid heart rate, and shortness of breath. Severe episodes can require blood transfusions (Cappellini & Fiorelli, 2008).

Checking Your DNA for G6PD Variants

If you have raw genetic data from 23andMe, AncestryDNA, or another direct-to-consumer testing service, you can check for the most common G6PD variants. The key SNPs to look for:

• rs1050828 (G6PD A- variant, 202G>A): The G allele is normal; the A allele indicates the deficient variant. Found on 23andMe v5 chip.
• rs1050829 (G6PD A variant, 376A>G): The A allele is the ancestral form; the G allele is associated with the A+ polymorphism and, combined with rs1050828, defines G6PD A-.
• rs5030868 (G6PD Mediterranean, 563C>T): The C allele is normal; the T allele indicates the Mediterranean variant.

Remember that because G6PD is on the X chromosome, males have only one copy. A single deficient allele in a male means full deficiency. Females need to consider that X-inactivation patterns can vary - a heterozygous female may have anywhere from near-normal to significantly reduced enzyme activity depending on which X chromosome is active in her red blood cell precursors (Luzzatto et al., 2020).

For a comprehensive analysis of your G6PD status alongside hundreds of other health-relevant variants, you can upload your raw DNA data to GenomeInsight for a detailed genetic health report.

What You Can Do About It

If you discover you carry a G6PD-deficient variant, here's what to do:

• Tell your doctor and pharmacist. G6PD deficiency should be listed as an allergy/condition in your medical record. This is a pharmacogenomic condition - knowing your status can prevent dangerous drug reactions. Learn more about how your DNA affects medication response in our pharmacogenomics guide.
• Carry a medical alert. Consider a medical ID bracelet or card listing G6PD deficiency, especially if you have a severe variant.
• Avoid known triggers. Keep a list of medications and foods to avoid. The G6PD Deficiency Association maintains a comprehensive and regularly updated drug safety list.
• Know the signs. Dark urine, sudden fatigue, and jaundice after starting a new medication or eating fava beans are red flags - seek medical attention immediately.
• Screen newborns. G6PD deficiency is a common cause of neonatal jaundice. If you or your partner carry the variant, mention it to your pediatrician. Some countries include G6PD in newborn screening panels, but many do not (Kaplan et al., 2011).
• Get tested formally. Raw DNA data can identify common variants, but a clinical G6PD enzyme activity test measures your actual enzyme levels. This is important because over 200 variants exist, and consumer DNA chips only test for a few (Minucci et al., 2012).

Explore your complete genetic health profile, including carrier status and pharmacogenomics, by uploading your DNA to GenomeInsight. Stay up to date with the latest in genetic health by joining our newsletter.

Key Takeaways

• G6PD deficiency is the world's most common enzyme deficiency, affecting 400–500 million people, predominantly in populations with African, Mediterranean, and Asian ancestry.
• It's X-linked - males are more commonly and more severely affected, but carrier females can also experience symptoms.
• The deficiency persists because it protects against malaria, similar to sickle cell trait - a classic example of balanced natural selection.
• Most people are asymptomatic until they encounter a trigger: certain medications (primaquine, dapsone, sulfa drugs), infections, or fava beans.
• Common DNA variants like rs1050828 (G6PD A-) and rs5030868 (G6PD Mediterranean) can be identified in raw genetic data from consumer DNA tests.
• Tell your healthcare providers if you carry a G6PD variant - it directly impacts which medications are safe for you.
• Formal enzyme testing complements genetic testing and is recommended for a definitive diagnosis.

References

Cappellini, M. D., & Fiorelli, G. (2008). Glucose-6-phosphate dehydrogenase deficiency. The Lancet, 371(9606), 64–74. https://doi.org/10.1016/S0140-6736(08)60073-2

Chinevere, T. D., Murray, C. K., Grant, E., Johnson, G. A., Duelm, F., & Hospenthal, D. R. (2006). Prevalence of glucose-6-phosphate dehydrogenase deficiency in U.S. Army personnel. Military Medicine, 171(9), 905–907. https://doi.org/10.7205/MILMED.171.9.905

Clark, T. G., Fry, A. E., Auburn, S., Campino, S., Diakite, M., Green, A., ... & Rockett, K. A. (2009). Allelic heterogeneity of G6PD deficiency in West Africa and severe malaria susceptibility. European Journal of Human Genetics, 17(8), 1080–1085. https://doi.org/10.1038/ejhg.2009.8

Howes, R. E., Piel, F. B., Patil, A. P., Nyangiri, O. A., Gething, P. W., Dewi, M., ... & Hay, S. I. (2012). G6PD deficiency prevalence and estimates of affected populations in malaria endemic countries: A geostatistical model-based map. PLoS Medicine, 9(11), e1001339. https://doi.org/10.1371/journal.pmed.1001339

Kaplan, M., Hammerman, C., & Bhutani, V. K. (2011). Parental education and the WHO neonatal G-6-PD screening program: A quarter century later. Journal of Perinatology, 31(3), 147–149. https://doi.org/10.1038/jp.2010.136

Luzzatto, L., Ally, M., & Notaro, R. (2020). Glucose-6-phosphate dehydrogenase deficiency. Blood, 136(11), 1225–1240. https://doi.org/10.1182/blood.2019000944

Minucci, A., Moradkhani, K., Hwang, M. J., Zuppi, C., Giardina, B., & Capoluongo, E. (2012). Glucose-6-phosphate dehydrogenase (G6PD) mutations database: Review of the "old" and update of the new mutations. Blood Cells, Molecules, and Diseases, 48(3), 154–165. https://doi.org/10.1016/j.bcmd.2012.01.001

Nkhoma, E. T., Poole, C., Vannappagari, V., Hall, S. A., & Beutler, E. (2009). The global prevalence of glucose-6-phosphate dehydrogenase deficiency: A systematic review and meta-analysis. Blood Cells, Molecules, and Diseases, 42(3), 267–278. https://doi.org/10.1016/j.bcmd.2008.12.005

Tishkoff, S. A., Varkonyi, R., Cahinhinan, N., Abbes, S., Argyropoulos, G., Destro-Bisol, G., ... & Clark, A. G. (2001). Haplotype diversity and linkage disequilibrium at human G6PD: Recent origin of alleles that confer malarial resistance. Science, 293(5529), 455–462. https://doi.org/10.1126/science.1061573

Uyoga, S., Ndila, C. M., Macharia, A. W., Nyuber, G., Shah, S., Peshu, N., ... & Williams, T. N. (2015). Glucose-6-phosphate dehydrogenase deficiency and the risk of malaria and other diseases in children on the coast of Kenya. The Lancet Haematology, 2(10), e437–e444. https://doi.org/10.1016/S2352-3026(15)00152-0

World Health Organization. (2022). Technical consultation to review the classification of glucose-6-phosphate dehydrogenase (G6PD). WHO Malaria Policy Advisory Group. https://www.who.int/publications/i/item/9789240045323

Youngster, I., Arcavi, L., Schechmaster, R., Akayzen, Y., Popliski, H., Shimonov, J., ... & Berkovitch, M. (2010). Medications and glucose-6-phosphate dehydrogenase deficiency: An evidence-based review. Drug Safety, 33(9), 713–726. https://doi.org/10.2165/11536520-000000000-00000

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