كروموسوم 22 (بشري)

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الكروموسوم 22، هو واحد من 23 زوج من الكروموسومات البشرية. عادة ما يمتلك البشر زوجان من هذا الكروموسوم. الكروموسوم 22 هو ثاني أصغر كروموسوم بشري (الكروموسوم 21 هو الأصغر)، يحتوي على حوالي 49 مليون زوج قاعدي (مادة بناء الدنا). ويمثل حوالي 1.5%-2% من إجمالي الدنا في الخلايا.

في 1991، أعلن الباحثون العاملون على مشروع الجينوم البشري عن تحديدهم لتسلسل الأزواج القاعدية الموجودة في هذا الكروموسوم. كان الكروموسوم 22 أول كرمومسوم بشري يتم تحديد تسلسله بالكامل.[1]

نظراً لاختلاف المناهج التي يستخدمها الباحثون في التنبؤ بعدد الجينات في كل كروموسوم، هناك تباين في أعداد الجينات المقدرة. من الأرجح أن الكروموسوم 22 يحتوي على 693 جين.

يعرف الكرمومسوم 22 في الأصل على أنه أصغر كروموسوم بشري، لكن وبعد أبحاث موسعة، توصل الباحثون إلى أن الكرومسوم 21 هو الأصغر. لم يعاد ترقيم هذه الكروموسومات لأن الكروموسوم 21 اشتهر بتعيينه ككروموسوم يمكن أن يسبب متلازمة داون.

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الجينات

الجدول التالي للجينات الموجودة على الكروموسوم 22:

الموضع الجين الوصف الحالة الطبية
22q11.1-q11.2 IGL@ immunoglobulin lambda locus - contains genes for the light chains of antibodies
22q11.21 TBX1 T-box 1
22q11 RTN4R Reticulon 4 receptor انفصام الشخصية
22q11.21-q11.23 COMT catechol-O-methyltransferase gene
22q12.1-q13.1 NEFH neurofilament, heavy polypeptide 200kDa
22q12.1 CHEK2 CHK2 checkpoint homolog (S. pombe)
22q12.2 NF2 neurofibromin 2 bilateral acoustic neuroma
22q13 SOX10 SRY (sex determining region Y)-box 10
22q13.2 EP300 E1A binding protein p300
22q13.3 WNT7B Wingless-type MMTV integration site family, member 7B
22q13.3 SHANK3 SH3 and multiple ankyrin repeat domains 3 22q13 deletion syndrome


الأمراض والاضطرابات

القائمة التالية لبعض الأمراض المرتبطة بالجينات الموجودة على الكروموسوم 22:

الحالات الكروموسومية

القائمة التالية للحالات الطبية التي تسببها تغيرات في بنية أو عدد نسخ الكروموسوم 22:

  • 22q11.2 deletion syndrome: Most people with 22q11.2 deletion syndrome are missing about 3 million base pairs on one copy of chromosome 22 in each cell. The deletion occurs near the middle of the chromosome at a location designated as q11.2. This region contains about 30 genes, but many of these genes have not been well characterized. A small percentage of affected individuals have shorter deletions in the same region.
    The loss of one particular gene, TBX1, is thought to be responsible for many of the characteristic features of 22q11.2 deletion syndrome, such as heart defects, an opening in the roof of the mouth (a cleft palate), distinctive facial features, and low calcium levels. A loss of this gene does not appear to cause learning disabilities, however. Other genes in the deleted region are also likely to contribute to the signs and symptoms of 22q11.2 deletion syndrome.
  • 22q11.2 distal deletion syndrome
  • 22q13 deletion syndrome (Phelan-McDermid syndrome): The deletion of the distal tip of the chromosome 22 is related to moderate to severe developmental delay and mental retardation. This region includes the Shank3 gene, thought to be responsible for the neurological deficits of the syndrome (Wilson et al., 2003).
    Almost all children affected by the 22q13 deletion have absent or severely delayed speech; minor facial dysmorphism; thin, flaky toenails; large, fleshy hands; large feet; prominent, poorly formed ears and other characteristics which are not visually apparent: hypotonia (97%); normal to accelerated growth (95%); increased tolerance to pain (86%); seizures (unknown percentage) [1].
  • Other chromosomal conditions: Other changes in the number or structure of chromosome 22 can have a variety of effects, including mental retardation, delayed development, physical abnormalities, and other medical problems. These changes include an extra piece of chromosome 22 in each cell (partial trisomy), a missing segment of the chromosome in each cell (partial monosomy), and a circular structure called ring chromosome 22 that is caused by the breakage and reattachment of both ends of the chromosome.
  • متلازمة عين القط is a rare disorder most often caused by a chromosomal change called an inverted duplicated 22. A small extra chromosome is made up of genetic material from chromosome 22 that has been abnormally duplicated (copied). The extra genetic material causes the characteristic signs and symptoms of cat-eye syndrome, including an eye abnormality called ocular iris coloboma (a gap or split in the colored part of the eye), small skin tags or pits in front of the ear, heart defects, kidney problems, and, in some cases, delayed development.
  • A rearrangement (translocation) of genetic material between chromosomes 9 and 22 is associated with several types of blood cancer (leukemia). This chromosomal abnormality, which is commonly called the Philadelphia chromosome, is found only in cancer cells. The Philadelphia chromosome has been identified in most cases of a slowly progressing form of blood cancer called chronic myeloid leukemia, or CML. It also has been found in some cases of more rapidly progressing blood cancers (acute leukemias). The presence of the Philadelphia chromosome can help predict how the cancer will progress and provides a target for molecular therapies.
  • Emanuel Syndrome is a translocation of chromosomes 11 and 22. Originally known as Supernumerary der(22) Syndrome, it occurs when an individual has an extra chromosome composed of pieces of the 11th and 22nd chromosomes.

المصادر

  1. ^ Mayor, Susan (1999). "First human chromosome is sequenced". BMJ. BMJ Group. 319 (7223): 1453. PMC 1117192. Retrieved 18 May 2013.

قراءات إضافية

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