Glucose-6-phosphate dehydrogenase deficiency

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is caused by mutations in the G6PD __ gene. This gene gives the body instructions to make an enzyme called G6PD, which is involved in processing carbohydrates. This enzyme also protects red blood cells from potentially harmful molecules called reactive oxygen species. Chemical reactions involving G6PD produce compounds that prevent reactive oxygen species from building up to toxic levels within red blood cells.

Mutations in the G6PD gene lower the amount of G6PD or alter its structure, lessening its ability to play its protective role. As a result, reactive oxygen species can accumulate and damage red blood cells. Factors such as infections, certain drugs, or eating fava beans can increase the levels of reactive oxygen species, causing red blood cells to be destroyed faster than the body can replace them. This reduction of red blood cells causes the signs and symptoms of hemolytic anemia in people with G6PD deficiency.

G6PD deficiency is inherited in an X-linked recessive manner. X-linked recessive conditions are much more common in males, who have only one X chromosome (and one Y chromosome). Females have two X chromosomes, so if they have a mutation on one of them, they still have one X chromosome without the mutation. Females with one X chromosome mutation are known as carriers and are usually unaffected. However, females can be affected if they have a mutation in both copies of the G6PD gene, or in some cases, if they have only one mutation. Females with one mutation may have lower G6PD activity than would normally be expected due to a phenomenon called skewed lyonization.

If a mother is a carrier of an X-linked recessive condition and the father is not, the risk to each child depends on whether the child is male or female.

• Each son has a 50% chance to be unaffected, and a 50% chance to be affected
• Each daughter has a 50% chance to be unaffected, and a 50% chance to be a carrier

If a father has the condition and the mother is not a carrier, all sons will be unaffected, and all daughters will be carriers.

There is nothing either parent can do, before or during a pregnancy, to cause a child to have this condition.

Females can have symptoms of G6PD deficiency. Females can be affected if they have a mutation in both copies of the G6PD gene, or in some cases, if they have only one mutated G6PD gene.

Depending on how mutations affect G6PD enzyme activity, symptoms in any individual can range from mild to severe. Females with mutations in both of their G6PD gene copies can experience the full range of symptoms similar to affected males (who have one mutation). Females who have one G6PD mutation can also have mild to severe symptoms as a result of a phenomenon called skewed lyonization. This phenomenon is also referred to as skewed X-inactivation.

Because females have two X chromosomes and males have one X chromosome, one copy of the X chromosome in each of a female's cells is "inactivated." This is to prevent females from having twice as much genetic information coming from the X chromosome. Typically, the "choice" of which X chromosome to inactivate is random, which theoretically would lead to each X chromosome being inactivated around 50% of the time. However, in come cases, the activation is skewed, leading to one X chromosome being inactivated significantly more than the other. If a female has a G6PD mutation on the X chromosome that is significantly more active, she can have mild to severe symptoms of G6PD deficiency. The severity depends on how the mutation affects G6PD activity, and the extent to which X-chromosome inactivation is skewed.

No. A person cannot acquire G6PD deficiency from a blood transfusion from a donor with G6PD. G6PD is a genetic disorder and is inherited in an X-linked recessive manner.

Due to many unanswered questions, there is controversy about whether G6PD- deficient people should become blood donors and about the quality of their blood during processing and storage. Risk factors associated with the use of G6PD-deficient blood in transfusion have not been well established. There is little evidence that G6PD-deficient people should be excluded from donating red blood cells. But, most studies on newborns and children have recommended routine screening for G6PD deficiency because their immature hepatic (liver) function potentially lessens their ability to handle any excess bilirubin. Transfusions of G6PD-deficient blood also may potentially have negative effects on premature newborns, or people who need repeated transfusions. For these recipients, screening for G6PD deficiency may be appropriate. The potential effects may differ depending on the region, the specifics of the recipient, the quantity transfused, and the type of G6PD deficiency.

The World Health Organization (WHO) guidelines recommend that blood be accepted from “individuals with G6PD deficiency or other inherited red cell membrane defects, without a history of hemolysis; however, their blood is not suitable for intrauterine transfusion, neonatal exchange transfusion or for patients with G6PD deficiency." According to the G6PD Deficiency Association, the Red Cross does not accept G6PD deficient blood.

Blood sugar or "glucose" is made when carbohydrates are broken down. Glucose-6-phosphate dehydrogenase is one enzyme involved in the pentose phosphate pathway, a pathway which processes glucose. The main reasons for this pathway is actually not to metabolize dietary sugars but to make ribose-5-phosphate which is important for making DNA and RNA, and to make NADPH which is important for protecting cells from potentially harmful molecules called reactive oxygen species. There are other enzymatic pathways in the body that exist to metabolize dietary sugars, for example the Krebb cycle, so when there is a deficiency of glucose-6-phosphate dehydrogenase the primary concern is for the impact the defeciency may have on the body as a result of a lack of ribose-5-phosphate and NADPH, and not necessarily its affect on blood sugar.

To learn more about how your body metabolizes food visit the Nemours: Kids Health Web site resource page on this topic at the following link:
http://kidshealth.org/parent/general/body_basics/metabolism.html

There has been some evidence that males with G6PD deficiency may be protected against severe malaria. It has been noted that the distribution of individuals with G6PD deficiency corresponds to areas in which malaria is, or has been, common. This has led to speculation that the prevalence of malaria has influenced the gene pool of populations in these areas, favoring the presence of the G6PD deficiency trait. It is possible that the frequency of malaria is lower in individuals with G6PD deficiency; however, a protective effect against uncomplicated malaria has not been conclusively verified.

Another association between G6PD deficiency and malaria is that hemolytic anemia in G6PD- deficient individuals is known to be triggered by a number of things, including anti-malarial drugs. Individuals should be screened for the G6PD defect before being treated with anti-malarials and other medications.

You can find relevant journal articles on glucose 6 phosphate dehydrogenase deficiency specific to adults through a service called PubMed, a searchable database of medical literature. Information on finding an article and its title, authors, and publishing details is listed here. Some articles are available as a complete document, while information on other studies is available as a summary abstract. To obtain the full article, contact a medical/university library (or your local library for interlibrary loan), or order it online using the following link. Using "glucose 6 phosphate dehydrogenase deficiency[ti] AND adults" as your search term should locate articles. To narrow your search, click on the "Limits" tab under the search box and specify your criteria for locating more relevant articles. Click here to view a search.
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed

The National Library of Medicine (NLM) Web site has a page for locating libraries in your area that can provide direct access to these journals (print or online). The Web page also describes how you can get these articles through interlibrary loan and Loansome Doc (an NLM document-ordering service). You can access this page at the following link http://nnlm.gov/members/. You can also contact the NLM toll-free at 888-346-3656 to locate libraries in your area.

The most important aspect of management for G6PD deficiency is to avoid agents that might trigger an attack. In cases of acute hemolytic anemia, a blood transfusion or even an exchange transfusion may be required.

The G6PD Deficiency Association, which is an advocacy group that provides information and supportive resources to individuals and families affected by G6PD deficiency, provides a list of drugs and food ingredients that individuals with this condition should avoid. They also maintain a list of low risk drugs that are generally safe to take in low doses.

The Newborn Screening Coding and Terminology Guide has information on the standard codes used for newborn screening tests. Using these standards helps compare data across different laboratories. This resource was created by the National Library of Medicine.