葡萄糖-6-磷酸脱氢酶缺乏症(G6PD) 简介(英文)

What is G6PD deficiency?

Glucose-6-phosphate dehydrogenase deficiency, or G6PD deficiency for short, is the

most common “inborn metabolic disorder” in the world. This means that from the time a

baby is born, thre is already something wrong with how his body makes and breaks

important substances. According to statistics, about 400 million people have G6PD

deficiency, and it is most common in Africa, Southeast Asia and the Middle

with G6PD deficiency have very little or no enzyme called Glucose-6-Phosphate

Dehydrogenase (G6PD). An enzyme is a kind of protein that speeds up chemical

reactions in the body. The enzyme G6PD is especially important to red blood cells. If this

enzyme is lacking or missing, red blood cells are easily destroyed.

Another name for G6PD deficiency is favism because some people who have it, usually

those living in the Meditteranean region, react very badly to fava beans.

What causes G6PD deficiency?

In order to understand what causes G6PD deficiency, one must first learn a bit about

genes and chromosomes.

Genes are like the body’s blueprints. They contain instructions on how specific parts of the

body are made. For example, if the isntructions in your hair genes say your hair is black,

your hair will be black. Genes are packaged into threadlike structures called

chromosomes. A chromosome is very much like a beaded bracelet. The beads are the

different genes that give instructions for different part of the body; the entire bracelet is the

chromosome. Genes usually come and act in pairs. One member of a specific pair comes

from the father, and the other member comes from the mother. The members of a pair are

located on paired chromosomes.

All normal human beings have 23 pairs of chromosomes. Each of the first 22 pairs contain

the same number and kind of genes. The last and 23rd pair is the sex chromosomes.

They are different from the first 22 pairs in that they do not have the same number and

kind of genes. The sex chromosomes contain the genes that determine whether a baby

will be a girl or a boy.

There are 2 kinds of sex chromosomes, X and Y. All baby girls have two X chromosomes.

All baby boys have one X and one Y. The gene that gives instructions on how G6PD is

made is found in the X chromosome only, thus G6PD deficiency is described as X-linked.

If a baby girl gets one defective G6PD gene from either of her parents, she will not have

G6PD deficiency because she has another G6PD gene that can do the work (remember:

a baby girl has two X chromosomes, thus two G6PD genes). But if she gets two defective

G6PD genes from both her parents, she will have G6PD deficiency. On the other hand, a

baby boy whose G6PD gene is defective will surely get G6PD deficiency because the Y

chromosome has no G6PD gene.

A defective G6PD gene will give wrong instructions on how to make the enzyme G6PD.

As a result, too little or none of it is made.

What are the harmful effects of G6PD deficiency?

G6PD has a very small but strategic role in protecting the body from substances that can

cause damage to cells or oxidative substances. Because of this important role, G6PD is

normally found in all parts of the body. To be sure, most parts of the body also keep a

“spare” enzyme, one that can do the work of G6PD in case it is lacking or missing entirely.

Unfortunately, this is not the case with red blood cells. They do not have spare enzymes

that can do the work of G6PD. If a baby does not have enough G6PD, his red blood cells

lack protection from the harmful effects of oxidative substances.

A baby with G6PD deficiency appears and remains healthy until he is exposed to a large

amount of oxidative substances. When this happens, his red blood cells are destroyed, a

process known as hemolysis.

Red blood cells carry oxygen to all parts of the body. When they undergo hemolysis, the

baby will have hemolytic anemia. The signs and symptoms of hemolytic anemia are

paleness, dizziness, headache, tea-colored urine, and abdominal or back pain or both.

Hemolytic anemia, when very severe, can end in death. Destroyed red blood cells are

brought to the liver to be broken down to smaller pieces for disposal. One of the end

products of this process is bilirubin, a yellowish substance that accumulates in different

parts of the body when too much of it is produced. Quite often, bilirubin accumulates in the

skin and causes it to appear yellowish. In the worst cases, biliribin accumulates in the

brain and causes mental retardation or death.

Where do oxidative substances come from?

Hemolysis of red blood cells will only occur IF and WHEN a G6PD deficient child is

exposed to oxidative substances. Oxidative substances are found in certain drugs, foods,

and beverages. The body also produces oxidative substances during severe infections or

illnesses such as typhoid fever, pneumonia, or kidney failure.

Most drugs with strong oxidative effects are of kinds:

1. antibiotics of the sulfa group

2. medicines for malaria

3. some medicines for fever

How is G6PD deficiency treated?

When a child has taken oxidative substances and suddenly shows the signs and

symptoms of hemolytic anemia, he is said to have a hemolytic crisis. During such crisis,

the goal of doctors and nurses is to prevent the harmful effects from getting worse. Blood

transfusion, oxygen, and folic acid may be given.

The ultimate treatment for G6PD deficiency is gene theraphy (replacing a defective gene

with a good one), but this is not yet available at the present time.

G6PD Deficiency Diet

G6PD deficiency occurs when your body does not produce adequate amounts of

glucose-6-phosphate dehydrogenase, an enzyme that assists proper red blood cell function. This

inherited condition affects about 400 million people worldwide, according to the Deployment

Health and Family Readiness Library. Although chronic stress, infections and prescription

medications can initiate hemolytic episodes -- periods when a lack of the G6PD enzyme can cause

fatigue, jaundice, dark urine or an elevated heart rate -- you can also experience these potentially

life-threatening symptoms after ingesting certain foods. Therefore, it is wise to follow the

recommended G6PD diet to remain asymptomatic.

Approved Foods

Photo Caption Consume coconut oil. Photo Credit joanna wnuk/iStock/Getty Images

Consume fats from natural fat sources such as coconut oil, olive oil, palm oil or animal fat. Obtain

your vitamins and minerals from natural sources such as bone stock soups. Round out your diet

with proteins and carbohydrates not found on the G6PD Deficiency forbidden foods list.

Forbidden Foods

Photo Caption Avoid mints and menthol. Photo Credit arinahabich/iStock/Getty Images

The G6PD Deficiency website lists several foods that you should not eat at any time. Do not

consume foods or supplements that contain large amounts of VItamin C, also called ascorbic acid,

or artificial blue dyes. Do not eat menthol, or menthol-containing foods such as breath mints or

candy. Do not eat legumes, such as lima beans, fava beans, kidney beans or soybeans. Avoid any

soy-containing products, such as tofu, bean curds, miso or textured soy protein. Look out for less

easily recognizable legumes such as alfalfa sprouts, peanuts, licorice or carob. Some legumes --

such as fava beans -- cause severe hemolysis -- but several other legumes, beans and pulses

cause less severe hemolysis that, while mild enough to evade initial detection, can still damage

your health.

Additional foods forbidden by include peas such as green peas, field peas

and black-eyed peas, beans such as black beans or refried beans and edible pods such as Chinese

pea pods and snow peas. Do not drink tonic water or eat bitter melon, a vegetable common in

African and Asian cuisine. Finally, do not eat refined sugar, high-fructose corn syrup or white

flour.