Causes of G6PD Deficiency
Glucose-6-phosphate dehydrogenase deficiency is a genetic disorder - meaning it’s passed down from parents to their offspring - that is characterized by an enzyme defect due to a mutated G6PD gene. The G6PD gene provides instructions for making the glucose-6-phosphate dehydrogenase enzyme, which helps protect red blood cells from damage due to reactive oxygen species (a type of free radical) and destruction. The same enzyme also helps the body to process and use glucose from carbohydrates. It’s needed to help turn carbohydrates obtained from the person’s diet into usable energy, which is why the deficiency and anemia are linked with symptoms like fatigue.

Due to the inheritance pattern of G6PD, the condition is much more likely to affect males compared to females. G6PD is inherited in an "X-linked recessive pattern," meaning the gene associated with the condition is located on the X chromosome, of which males have only one copy. Because males have only one X chromosome, but females have two, a male has a higher chance of developing G6PD. This is because he only has to inherit one copy of the defective gene from either parent, instead of two. Sons who have mothers who were either G6PD deficient, or were "healthy carriers" of the mutation (the mom does not display symptoms), are most likely to inherit the condition themselves. 

Symptoms of hemolytic anemia are due to decreased levels of red blood cells. Risk factors for developing hemolytic anemia symptoms related to G6PD deficiency include:

Suffering from an illness, including a virus or infection

Taking certain drugs/medications that cause negative reactions (listed below), contributing to red blood cells being destroyed faster than the body can replace them.

Ingesting certain foods, especially fava beans (and others listed below).

Some foods are capable of causing a negative reaction in people with G6PD deficiency, but not every person with the deficiency will have these reactions.