G6PD Deficiency: The X-Linked Enzyme Condition Common in Southeast Asia — Foods and Drugs to Avoid

The 1-Minute Summary

• G6PD (Glucose-6-Phosphate Dehydrogenase) deficiency is one of the most common genetic conditions in the world, and is especially frequent across Southeast Asia, including Thailand.
• It is inherited in an X-linked pattern, so it shows up more clearly in men, but female carriers can have symptoms too.
• The key triggers are fava beans, infections, and certain medications that induce red blood cell breakdown.
• Most people have no symptoms until they meet a trigger, so many only find out they have it after a sudden episode of hemolysis.
• It is diagnosed by an enzyme-activity test or genetic testing, and complications are largely preventable by avoiding triggers.

Hello, from the Geneus DNA medical team. I want to introduce a condition that may sound obscure but is actually very close to home for many Thai families: G6PD deficiency. Many families first hear about it when a newborn develops jaundice, or when an older relative takes a certain medicine and suddenly passes dark-colored urine for no obvious reason. A correct understanding of this condition genuinely prevents serious events, and it is a great example of how genetic information can be used to look after yourself in everyday life.

What Is G6PD, and Why Does It Matter for Red Blood Cells?

The G6PD enzyme is the first enzyme in the pentose phosphate pathway. Its job is to produce NADPH, which acts like an "anti-rust shield" for red blood cells. NADPH keeps antioxidants such as glutathione regenerated and ready to neutralize oxidative stress at all times.

Red blood cells are unusual in that they have no nucleus and no mitochondria, so they rely almost entirely on this pathway to protect themselves from oxidants. When G6PD activity is lower than normal, red blood cells become especially fragile when they encounter something with oxidizing properties, leading to hemolysis (red blood cell breakdown). Possible signs include fatigue, pallor or jaundice, dark cola-colored urine, and in severe cases a rapid drop in blood counts requiring hospital care.

Why Is It So Common in Southeast Asia, and How Is It Inherited?

The G6PD gene sits on the X chromosome, which is why the condition is X-linked. Men have only one X chromosome, so if they inherit a deficient copy they usually show clear symptoms. Women have two X chromosomes; a woman with a single deficient copy is a "carrier," but because of random X-inactivation, some women can still have low enzyme levels and develop symptoms. So this should not be thought of as a men-only condition.

Interestingly, the condition is common in regions that historically had heavy malaria transmission — Africa, the Mediterranean, the Middle East, and Southeast Asia. Scientists believe G6PD deficiency may offer some advantage against malaria, so it has been favored and preserved in these populations through evolution. This is one reason it is fairly common among Thai people and is part of newborn screening in many areas.

Foods and Drugs to Avoid

The core of managing G6PD deficiency is avoiding oxidative triggers, which fall into three main groups.

1. Foods

• Fava beans (broad beans) are the most notorious trigger — so much so that the reaction is called "favism." Eating fava beans fresh, frozen, or processed can trigger hemolysis in some people with the deficiency.
• Be cautious with supplements and substances that have strong oxidant activity, such as very high-dose intravenous vitamin C, and always consult a doctor first.

2. Drugs

Several drug classes can trigger red blood cell breakdown in people with G6PD deficiency. Commonly cited examples include:

• Certain antimalarials such as primaquine and tafenoquine
• Some sulfonamides such as sulfamethoxazole, and dapsone
• The antibiotic nitrofurantoin
• Methylene blue and rasburicase
• The urinary analgesic phenazopyridine

The key point is: do not self-medicate, and always tell your doctor and pharmacist that you have G6PD deficiency before starting any new medicine — some of these are common, over-the-counter drugs. This connects to pharmacogenomics, the study of how each person's genetics affect their response to drugs, and it is distinct from genetics-related drug allergy, which works through a different mechanism.

3. Chemicals and Infections

• Naphthalene (mothballs) used to repel insects is a recognized trigger — take special care around infants and young children.
• Infections, both viral and bacterial, are among the most common triggers, because the body produces oxidants while fighting the infection.

What the Science Does Not Say, and Important Cautions

I want to be clear that having G6PD deficiency does not mean you will always have severe symptoms. Severity depends on the specific variant (there are many variants with different residual enzyme levels), the amount and type of trigger, and individual factors. Many people live entirely normal lives as long as they avoid triggers well.

On the other hand, lists of drugs and foods to avoid do not fully agree across sources, and the strength of evidence for some drugs varies — some are safe at normal doses but risky at high doses. So you should not make decisions on your own from an internet list. Genetic testing or enzyme measurement is just one piece of information, not a complete diagnosis or treatment order in itself. Whenever you notice unusual symptoms such as jaundice, dark urine, or sudden fatigue, see a doctor promptly, and always plan your medications together with your doctor and pharmacist.

References

1. MedlinePlus (NIH). Glucose-6-phosphate dehydrogenase deficiency. medlineplus.gov
2. Cappellini MD, Fiorelli G. Glucose-6-phosphate dehydrogenase deficiency. Lancet. 2008. pubmed.ncbi.nlm.nih.gov
3. Luzzatto L, Ally M, Notaro R. Glucose-6-phosphate dehydrogenase deficiency. Blood. 2020. pubmed.ncbi.nlm.nih.gov
4. Cleveland Clinic. G6PD Deficiency. my.clevelandclinic.org