X連鎖隱性遺傳

X連鎖隱性遺傳X-linked recessive inheritance)是孟德爾遺傳一種模式,其中X染色體基因突變導致表型總是在男性中表達(對於基因突變來說必然是純合,因為有一條X和一條Y染色體),在基因突變純合的女性中,參見合子。攜帶一份突變基因的女性是攜帶者。

X連鎖隱性遺傳
Patterns of X-linked recessive inheritance in a royal family

X連鎖遺傳是指導致性狀或疾病的基因位於X染色體上。女性有兩X染色體,而男性有一X染色體和一Y染色體。只有一個突變拷貝的攜帶者女性通常不會表現出表型,儘管X染色體失活英语X-chromosome inactivation傾斜X失活英语skewed X-inactivation)的差異會導致攜帶者不同程度的臨床表現女性,因為有些細胞會表達一個 X等位基因,而有些細胞會表達另一個。目前對已測序的X連鎖基因的估計是499個,包括模糊定義的性狀在內的總數是983個。[1]

繼承模式

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In humans, inheritance of X-linked recessive traits follows a unique pattern made up of three points.

  • The first is that affected fathers cannot pass X-linked recessive traits to their sons because fathers give Y chromosomes to their sons. This means that males affected by an X-linked recessive disorder inherited the responsible X chromosome from their mothers.
  • Second, X-linked recessive traits are more commonly expressed in males than females.[2] This is due to the fact that males possess only a single X chromosome, and therefore require only one mutated X in order to be affected. Women possess two X chromosomes, and thus must receive two of the mutated recessive X chromosomes (one from each parent). A popular example showing this pattern of inheritance is that of the descendants of Queen Victoria and the blood disease hemophilia.[3]
  • The last pattern seen is that X-linked recessive traits tend to skip generations, meaning that an affected grandfather will not have an affected son, but could have an affected grandson through his daughter.[4] Explained further, all daughters of an affected man will obtain his mutated X, and will then be either carriers or affected themselves depending on the mother. The resulting sons will either have a 50% chance of being affected (mother is carrier), or 100% chance (mother is affected). It is because of these percentages that we see males more commonly affected than females.

Pushback on recessive/dominant terminology

A few scholars have suggested discontinuing the use of the terms dominant and recessive when referring to X-linked inheritance.[5] The possession of two X chromosomes in females leads to dosage issues which are alleviated by X-inactivation.[6] Stating that the highly variable penetrance of X-linked traits in females as a result of mechanisms such as skewed X-inactivation or somatic mosaicism is difficult to reconcile with standard definitions of dominance and recessiveness, scholars have suggested referring to traits on the X chromosome simply as X-linked.[5]

Examples

Most common

The most common X-linked recessive disorders are:[7]

  • Red–green color blindness, a very common trait in humans and frequently used to explain X-linked disorders.[8] Between seven and ten percent of men and 0.49% to 1% of women are affected. Its commonness may be explained by its relatively benign nature. It is also known as daltonism.
  • Hemophilia A, a blood clotting disorder caused by a mutation of the Factor VIII gene and leading to a deficiency of Factor VIII. It was once thought to be the "royal disease" found in the descendants of Queen Victoria. This is now known to have been Hemophilia B (see below).[9][10]
  • Hemophilia B, also known as Christmas disease,[11] a blood clotting disorder caused by a mutation of the Factor IX gene and leading to a deficiency of Factor IX. It is rarer than hemophilia A. As noted above, it was common among the descendants of Queen Victoria.
  • Duchenne muscular dystrophy, which is associated with mutations in the dystrophin gene. It is characterized by rapid progression of muscle degeneration, eventually leading to loss of skeletal muscle control, respiratory failure, and death.
  • Becker's muscular dystrophy, a milder form of Duchenne, which causes slowly progressive muscle weakness of the legs and pelvis.
  • X-linked ichthyosis, a form of ichthyosis caused by a hereditary deficiency of the steroid sulfatase (STS) enzyme. It is fairly rare, affecting one in 2,000 to one in 6,000 males.[12]
  • X-linked agammaglobulinemia (XLA), which affects the body's ability to fight infection. XLA patients do not generate mature B cells.[13] B cells are part of the immune system and normally manufacture antibodies (also called immunoglobulins) which defends the body from infections (the humoral response). Patients with untreated XLA are prone to develop serious and even fatal infections.[14]
  • Glucose-6-phosphate dehydrogenase deficiency, which causes nonimmune hemolytic anemia in response to a number of causes, most commonly infection or exposure to certain medications, chemicals, or foods. Commonly known as "favism", as it can be triggered by chemicals existing naturally in broad (or fava) beans.[15]

Less common disorders

Theoretically, a mutation in any of the genes on chromosome X may cause disease, but below are some notable ones, with short description of symptoms:

另見

參考

  1. ^ OMIM X-linked Genes. nih.gov. [3 May 2018]. (原始内容存档于7 March 2016). 
  2. ^ Understanding Genetics: A New York, Mid-Atlantic Guide for Patients and Health Professionals. National Center for Biotechnology Information. 8 July 2009 [9 June 2020]. (原始内容存档于2022-11-27). 
  3. ^ History of Bleeding Disorders. National Hemophilia Foundation. 2014-03-04 [2020-06-09]. (原始内容存档于2020-11-12) (英语). 
  4. ^ Pierce, Benjamin A. Genetics: A Conceptual Approach. Macmillan Learning. 2020: 154–155. ISBN 978-1-319-29714-5. 
  5. ^ 5.0 5.1 Dobyns, William B.; Filauro, Allison; Tomson, Brett N.; Chan, April S.; Ho, Allen W.; Ting, Nicholas T.; Oosterwijk, Jan C.; Ober, Carole. Inheritance of most X-linked traits is not dominant or recessive, just X-linked. American Journal of Medical Genetics. 2004, 129A (2): 136–43. PMID 15316978. S2CID 42108591. doi:10.1002/ajmg.a.30123. 
  6. ^ Shvetsova, Ekaterina; Sofronova, Alina; Monajemi, Ramin; Gagalova, Kristina; Draisma, Harmen H. M.; White, Stefan J.; Santen, Gijs W. E.; Chuva de Sousa Lopes, Susana M.; Heijmans, Bastiaan T.; van Meurs, Joyce; Jansen, Rick. Skewed X-inactivation is common in the general female population. European Journal of Human Genetics. March 2019, 27 (3): 455–465. ISSN 1476-5438. PMC 6460563 . PMID 30552425. doi:10.1038/s41431-018-0291-3  (英语). 
  7. ^ GP Notebook - X-linked recessive disorders 互联网档案馆存檔,存档日期2011-06-13. Retrieved on 5 Mars, 2009
  8. ^ OMIM Color Blindness, Deutan Series; CBD. nih.gov. [3 May 2018]. (原始内容存档于29 September 2009). 
  9. ^ Michael Price. Case Closed: Famous Royals Suffered From Hemophilia. ScienceNOW Daily News. AAAS. 8 October 2009 [9 October 2009]. (原始内容存档于20 October 2013). 
  10. ^ Rogaev, Evgeny I.; Grigorenko, Anastasia P.; Faskhutdinova, Gulnaz; Kittler, Ellen L. W.; Moliaka, Yuri K. Genotype Analysis Identifies the Cause of the 'Royal Disease'. Science. 2009, 326 (5954): 817. Bibcode:2009Sci...326..817R. PMID 19815722. S2CID 206522975. doi:10.1126/science.1180660. 
  11. ^ "Hemophilia B". 互联网档案馆存檔,存档日期2007-12-01. National Hemophilia Foundation.
  12. ^ Carlo Gelmetti; Caputo, Ruggero. Pediatric Dermatology and Dermatopathology: A Concise Atlas. T&F STM. 2002: 160. ISBN 1-84184-120-X. 
  13. ^ X-linked Agammaglobulinemia: Immunodeficiency Disorders: Merck Manual Professional. [2008-03-01]. (原始内容存档于2008-02-18). 
  14. ^ Diseases Treated at St. Jude. stjude.org. [3 May 2018]. (原始内容存档于15 August 2007). 
  15. ^ Favism - Doctor. patient.info. [3 May 2018]. (原始内容存档于21 November 2017). 

外部鏈接

[Female X-linked disorders]