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 East.Babies 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 G6PDDeficiency.org 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.