5.14 遗传疾病
Section outline
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Polly Who?
::波莉谁?Each hand in this photo has an extra pinky finger. This is a condition called polydactyly, which literally means "many digits." People with polydactyly may have extra fingers and/or toes, and the condition may affect just one hand or foot, or both hands and feet. Polydactyly is often genetic in origin and may be part of a genetic disorder associated with other abnormalities.
::照片中的每只手都有一个额外的小指头。 这是一个叫做“多细胞细胞”的状态, 意思是“许多数字 ” 。 多细胞的人可能有额外的手指和/或脚趾, 并且这种状态可能只影响到一只手或脚, 或双手和脚。 多细胞往往是遗传的起源, 并且可能是与其他异常有关的基因紊乱的一部分。What Are Genetic Disorders?
::什么是遗传病?Genetic disorders are diseases, syndromes, or other abnormal conditions caused by in one or more genes , or by chromosomal alterations . Genetic disorders are typically present at birth, but they should not be confused with congenital disorders , a category that includes any disorder present at birth, regardless of cause. Some congenital disorders are not caused by genetic mutations or chromosomal alterations. Instead, they are caused by problems that arise during embryonic or fetal , or during the process of birth. An example of a nongenetic congenital disorder is fetal alcohol syndrome. This is a collection of birth defects, including facial anomalies and intellectual disability, caused by maternal alcohol consumption during .
::遗传性疾病是指一种或多种基因或染色体变异引起的疾病、综合症或其他异常情况,遗传性疾病通常在出生时就存在,但不应与先天性疾病相混淆,先天性疾病包括任何先天性疾病,不论原因为何,某些先天性疾病不是遗传变异或染色体变异引起的,而是胚胎或胎儿或出生过程中出现的问题造成的,非遗传性先天性疾病的例子之一是胎儿酒精综合症,这是一系列先天性缺陷,包括面部畸形和智力残疾,是由母亲饮酒引起的。Genetic Disorders Caused by Mutations
::变异引起的遗传疾病The table lists several genetic disorders caused by mutations in just one gene. Some of the disorders are caused by mutations in autosomal genes, others by mutations in X-linked genes . Which disorders would you expect to be more common in males than females?
::表格列出了只由一个基因突变引起的几种遗传性疾病,有些是由自主基因突变引起的,有些则是由X相关基因突变引起的。 你期望男性的哪一种疾病比女性更常见?Genetic Disorder Direct Effect of Mutation Signs and Symptoms of the Disorder Mode of Inheritance Marfan syndrome defective in connective tissue heart and defects and unusually long, slender limbs and fingers autosomal dominant Sickle anemia abnormal hemoglobin protein in red blood cells sickle-shaped red blood cells that clog tiny , causing pain and damaging organs and autosomal recessive Vitamin D-resistant rickets lack of a substance needed for bones to absorb minerals soft bones that easily become deformed, leading to bowed legs and other skeletal deformities X-linked dominant Hemophilia A reduced activity of a protein needed for clotting internal and external bleeding that occurs easily and is difficult to control X-linked recessive Very few genetic disorders are controlled by dominant mutant . A dominant allele is expressed in every individual who inherits even one copy of it. If it causes a serious disorder, affected people may die young and fail to reproduce. Therefore, the mutant dominant allele is likely to die out of a .
::很少有遗传病是由占支配地位的变种人控制的。 每一个继承者都表现出占支配地位的异种。 如果它造成严重的紊乱,受影响的人可能会年轻死亡,不会繁殖。 因此, 占支配地位的变种人很可能死于某一个变种。A recessive mutant allele — such as the allele that causes sickle cell anemia or cystic fibrosis — is not expressed in people who inherit just one copy of it. These people are called carriers . They do not have the disorder themselves, but they carry the mutant allele and their offspring can inherit it. Thus, the allele is likely to pass on to the next generation, rather than die out.
::造成镰状细胞贫血或细胞纤维化的止息变异体异变异体,如导致镰状细胞贫血或细胞纤维化的异变异体,并不表现在只继承一份变异体的人身上,这些人被称为携带者,他们自己没有病症,但他们携带变异异异异体异变异体,他们的后代可以继承。因此,异变异体可能传给下一代,而不是死亡。Genetic Disorders Caused by Chromosomal Alterations
::染色体改变导致的遗传疾病Mistakes may occur during that result in nondisjunction . This is the failure of replicated to separate properly during meiosis. Some of the resulting gametes will be missing all or part of a chromosome, while others will have an extra copy of all or part of the chromosome. If such gametes are fertilized and form zygotes , they usually do not survive. If they do survive, the individuals are likely to have serious genetic disorders.
::在这种结果中,错误可能会发生,造成不相容的结果。这就是,在美化期间,无法复制正确分离。 由此产生的一些调子将全部或部分丢失染色体, 而另一些则会额外复制全部或部分染色体。 如果这些调子被施肥并形成zygotes, 它们通常不会存活下来。 如果它们能存活下来, 个人可能患有严重的遗传障碍 。The table lists several genetic disorders that are caused by abnormal numbers of chromosomes. Most chromosomal disorders involve the X chromosome . The X and Y chromosomes are the only chromosome pair in which the two chromosomes are very different in size. This explains why nondisjunction tends to occur more frequently in sex chromosomes than in autosomes .
::表格列出了一些由异性染色体引起的遗传障碍,大多数染色体紊乱都涉及X染色体。X和Y染色体是唯一一种染色体,其中两种染色体的大小差异很大。这解释了为什么在性染色体中非交叉性往往比在异性体中更为频繁。Genetic Disorder Genotype Phenotypic Effects Down syndrome extra copy (complete or partial) of chromosome 21 (see figure below) developmental delays, distinctive facial appearance, and other abnormalities (see figure below) Turner’s syndrome one X chromosome but no other sex chromosome (XO) female with short height and infertility (inability to reproduce) Triple X syndrome three X chromosomes (XXX) female with mild developmental delays and menstrual irregularities Klinefelter’s syndrome one Y chromosome and two or more X chromosomes (XXY, XXXY) male with problems in sexual development and reduced levels of the male testosterone Trisomy 21 (Down Syndrome) Karyotype. A karyotype is a picture of a cell's chromosomes. In this case, note the extra chromosome 21. On the left, a child with Down syndrome, exhibiting characteristic facial appearance.
::Trisomy 21 (Down Insession) Karyotype。 Karyotype是细胞染色体的图片。 在这个例子中, 注意额外的染色体 21 。 在左边, 一个患有唐氏综合症的儿童, 表现出面部特征的面部外观 。Diagnosing and Treating Genetic Disorders
::诊断和治疗遗传病A genetic disorder that is caused by a mutation can be inherited. Therefore, people with a genetic disorder in their family may be concerned about having children with the disorder. A genetic counselor can help them understand the risks of their children being affected. If they decide to have children, they may be advised to have prenatal (“before birth”) testing to see if the fetus has any genetic abnormalities. One method of prenatal testing is amniocentesis . In this procedure, a few fetal cells are extracted from the fluid surrounding the fetus in utero , and the fetal chromosomes are examined. Down syndrome and other chromosomal alterations can be detected in this way.
::突变导致的遗传障碍可以遗传。因此,家庭遗传障碍患者可能担心有孩子患此病。遗传顾问可以帮助他们了解孩子受到影响的风险。如果他们决定生孩子,可以建议他们进行产前(“出生前”)测试,看胎儿是否有任何遗传异常。产前检测的一种方法是肾脏检查。在这个过程中,从子宫胎儿周围的液体中抽取了少数胚胎细胞,对胎儿染色体进行了检查。通过这种方式可以检测到唐氏综合症和其他染色体的改变。The symptoms of genetic disorders can sometimes be treated or prevented. In the genetic disorder called phenylketonuria (PKU), for example, the amino acid phenylalanine builds up in the body to harmful levels. PKU is caused by a mutation in a gene that normally codes for an needed to break down phenylalanine. When a person with PKU consumes foods high in phenylalanine ( including many high-protein foods), the buildup of PKU can lead to serious health problems. In infants and young children, the build-up of phenylalanine can cause intellectual disability and delayed development, along with other serious problems. Babies in the United States and many other countries are screened for PKU soon after birth. If PKU is diagnosed, the infant can be fed a low-phenylalanine diet, which prevents the buildup of phenylalanine and the health problems associated with it, including intellectual disability. As long as a low-phenylalanine diet is followed throughout life, most symptoms of the disorder can be prevented.
::例如,在被称为苯丙酮尿(PKU)的遗传疾病中,氨酸苯丙烯在身体中累积到有害水平。PKU是由一种基因突变造成的,这种基因通常对打破苯丙烯素的需要有编码。当PKU的人消费苯丙烯(包括许多高蛋白质食品)的高浓度食物时,PKU的积累会导致严重的健康问题。在婴儿和幼儿中,苯丙烯的积累可造成智力残疾和发育迟缓,并造成其他严重问题。美国和许多其他国家的婴儿出生后不久即接受PKU的检查。如果PKU被诊断,婴儿可以喂低苯丙烯饮食,从而防止苯丙烯的积累和与其相关的健康问题,包括智力残疾。只要在整个生命中都遵循低苯丙烯饮食,大多数症状都可以预防。Curing Genetic Disorders
::治疗遗传病Cures for genetic disorders are still in the early stages of development. One potential cure is . Gene therapy is an experimental technique that uses genes to treat or prevent disease. In gene therapy, normal genes are introduced into cells to compensate for abnormal genes. If a mutated gene causes a necessary protein to be nonfunctional or missing, gene therapy may be able to introduce a normal copy of the gene to produce the needed functional protein.
::基因障碍的症候仍处于早期发育阶段,一种潜在的治疗方法是:基因疗法是一种利用基因治疗或预防疾病的实验技术;在基因疗法中,正常基因被引入细胞以弥补异常基因;如果变异基因导致必要的蛋白质不能起作用或消失,基因疗法也许能够引入正常基因复制物来产生所需的功能蛋白质。A gene inserted directly into a cell usually does not function, so a carrier called a vector is genetically engineered to deliver the gene (see illustration ). Certain , such as adenoviruses, are often used as vectors. They can deliver the new gene by infecting cells. The viruses are modified so they do not cause disease when used in people. If the treatment is successful, the new gene delivered by the vector will allow the synthesis of a functioning protein. Researchers still must overcome many technical challenges before gene therapy will be a practical approach to curing genetic disorders.
::直接插入细胞的基因通常不起作用,因此一个称为矢量的载体经过基因工程改造来传递基因(见插图 ) 。 某些病毒,例如肾脏病毒,常常被用作病媒。 它们可以通过感染细胞来传递新的基因。 病毒被修改,因此在人体使用时不会引起疾病。 如果治疗成功,由矢量提供的新的基因将允许合成功能性蛋白。 研究人员仍然必须克服许多技术挑战,才能使基因疗法成为治疗基因紊乱的实用方法。Gene therapy is an experimental technique for curing a genetic disorder by changing the patient's genetic makeup. Typically, gene therapy involves introducing a normal copy of a mutant gene into the patient's cells.
::基因治疗是一种通过改变患者的基因构成来治愈基因紊乱的实验技术。 基因疗法通常涉及将基因基因基因正常复制引入患者细胞。Feature: Human Biology in the News
::特著:《新闻》中的人类生物学Down syndrome is the most common genetic cause of intellectual disability. It occurs in about one in every 700 live births, and it currently affects nearly half a million Americans. Until recently, scientists thought that the changes leading to intellectual disability in people with Down syndrome all happen before birth.
::唐氏综合症是智力残疾最常见的遗传原因。 每700个活产中就有1个发生,目前它影响到近50万美国人。 直到最近,科学家认为导致唐氏综合症患者智力残疾的变化都发生在出生前。Even more recently, researchers discovered a genetic abnormality that affects brain development in people with Down syndrome throughout childhood and into . The newly discovered genetic abnormality changes between nerve cells in the brain, resulting in slower transmission of . This finding may eventually allow the development of strategies to promote brain functioning in Down syndrome patients, and it may also be applicable to other development disabilities, such as autism. The results of this promising study were published in the March 16, 2016 issue of the scientific journal .
::最近,研究人员发现了影响患有唐氏综合症者的大脑发育的遗传异常,这种异常影响他们整个童年和进入。新发现的脑神经细胞之间的遗传异常变化导致脑神经细胞的传播速度减缓。这一发现最终可能有利于制定战略,促进唐氏综合症患者的大脑功能,还可能适用于其他发育障碍,如自闭症。这一大有希望的研究结果发表在2016年3月16日的《科学期刊》上。Summary
::摘要-
Genetic disorders are diseases, syndromes, or other abnormal conditions that are caused by mutations in one or more genes, or by chromosomal alterations.
::遗传疾病是指一种或多种基因突变或染色体改变引起的疾病、综合症或其他异常情况。 -
Examples of genetic disorders caused by single-gene mutations include Marfan syndrome (autosomal dominant), sickle cell anemia (autosomal recessive), vitamin D-resistant rickets (X-linked dominant), and hemophilia A (X-linked recessive). Very few genetic disorders are caused by dominant mutations because these alleles are less likely to be passed on to successive generations.
::单基因突变引起的遗传障碍的例子包括:马凡综合症(黄素占多数)、镰状细胞贫血(黄素消退)、抗维他命D抗性(X-连带主导)和血友病A(X-连带休眠),很少有遗传障碍是主要突变造成的,因为这些异象不太可能传给后代。 -
Nondisjunction is the failure of replicated chromosomes to separate properly during meiosis. This may result in genetic disorders caused by abnormal numbers of chromosomes. An example is Down syndrome, in which the individual inherits an extra copy of chromosome 21. Most chromosomal disorders involve the X chromosome. An example is Klinefelter's syndrome (XXY, XXXY).
::非相容性是指复制的染色体在梅氏病期间未能适当分离,这可能导致染色体数量异常造成的遗传障碍,例如唐氏综合症,其中个人继承了另外一份染色体21。大多数染色体紊乱都涉及X染色体。Klinefelter综合症(XXY,XXXY)就是一个例子。 -
Prenatal genetic testing (by amniocentesis, for example) can detect chromosomal alterations
in utero.
The symptoms of some genetic disorders can be treated or prevented. For example, symptoms of phenylketonuria (PKU) can be prevented by following a low-phenylalanine diet throughout life.
::产前遗传检测(例如,通过氨基血清检测)可以检测出子宫的染色体变化,某些遗传障碍的症状可以治疗或预防,例如,苯丙酮尿(PKU)的症状可以通过在整个生命中采用低苯丙烯饮食来预防。 -
Cures for genetic disorders are still in the early stages of development. One potential cure is gene therapy, in which normal genes are introduced into cells by a vector such as a virus to compensate for mutated genes.
::基因紊乱的症候仍处于早期发育阶段,一种潜在的解药是基因疗法,在这种疗法中,正常基因由病毒等媒介引入细胞,以弥补变异基因。
Review
::回顾1. Define genetic disorder.
::1. 界定遗传疾病的定义。2. Identify three genetic disorders caused by mutations in a single gene.
::2. 查明单一基因突变引起的三种遗传障碍。3. Why are single-gene genetic disorders more commonly controlled by recessive than dominant mutant alleles?
::3. 为什么单基因遗传疾病比主要变种异种异种更经常由休眠控制?4. What is nondisjunction? Why can it cause genetic disorders?
::4. 什么是非分离?为什么它会造成遗传疾病?5. Explain why genetic disorders caused by abnormal numbers of chromosomes most often involve the X chromosome.
::5. 解释为什么由异性染色体的异常数字引起的遗传疾病往往涉及X染色体。6. How is Down syndrome detected in utero ?
::6. 在子宫中如何检测到唐氏综合症?7. Use the example of PKU to illustrate how the symptoms of a genetic disorder can sometimes be prevented.
::7. 以PKU为例,说明有时如何预防遗传病症状。8. Explain how gene therapy works.
::8. 解释基因疗法如何运作。9. Compare and contrast genetic disorders and congenital disorders.
::9. 比较和对比遗传疾病和先天性疾病。10. Explain why parents that do not have Down syndrome can have a child with Down syndrome.
::10. 解释为什么没有唐氏综合症的父母可以有一个唐氏综合症的孩子。11. Hemophilia A and Turner’s syndrome both involve problems with the X chromosome. I n terms of how the X chromosome is affected, w hat is the major difference between these two types of disorders?
::11. 血友病A和特纳综合症都涉及X染色体的问题,就X染色体如何受到影响而言,这两类疾病的主要区别是什么?12. Can you be a carrier of Marfan syndrome and not have the disorder? Explain your answer.
::12. 你能否成为Marfan综合症的携带者,而不患有这种疾病?13. True or False: It is impossible for people to have more than three copies of one chromosome.
::13. 真实或假:人们不可能拥有一份染色体的3份以上。14. True or False: The gene for sickle cell anemia is on a sex chromosome.
::14. 真实或假:镰状细胞贫血的基因在性染色体上。Explore More
::探索更多Scientists have promised that gene therapy will be the next big leap for medicine, but what is it exactly? Learn more here:
::科学家已经承诺基因疗法将是医学的下一个重大飞跃,但究竟是什么?Imagine if we could fix a patient's own cells and cure their genetic disease once and for all, instead of treating their chronic illness slowly over time. Learn more about gene therapy here:
::想象一下,如果我们能修复病人自己的细胞,一劳永逸地治愈他们的基因疾病,而不是慢慢地治疗他们的慢性病。 -
Genetic disorders are diseases, syndromes, or other abnormal conditions that are caused by mutations in one or more genes, or by chromosomal alterations.
