The three major single chromosome mutations; deletion (1), duplication (2) and inversion (3).
The two major two chromosome mutations; insertion (1) and Translocation (2).
A chromosome anomaly, abnormality, aberration, or mutation is a missing, extra, or irregular portion of chromosomal DNA.[1] It can be from an atypical number of chromosomes or a structural abnormality in one or more chromosomes. Chromosome mutation was formerly used in a strict sense to mean a change in a chromosomal segment, involving more than one gene.[2] A karyotype refers to a full set of chromosomes from an individual that can be compared to a "normal" karyotype for the species via genetic testing. A chromosome anomaly may be detected or confirmed in this manner. Chromosome anomalies usually occur when there is an error in cell division following meiosis or mitosis. There are many types of chromosome anomalies. They can be organized into two basic groups, numerical and structural anomalies.
Contents
- 1 Numerical disorders
- 2 Structural abnormalities
- 3 Inheritance
- 4 Acquired chromosome abnormalities
- 5 See also
- 6 References
- 7 External links
Numerical disorders
This is called aneuploidy (an abnormal number of chromosomes), and occurs when an individual either is missing a chromosome from a pair (monosomy) or has more than two chromosomes of a pair (trisomy, tetrasomy, etc.).
In humans, an example of a condition caused by a numerical anomaly is Down Syndrome, also known as Trisomy 21 (an individual with Down Syndrome has three copies of chromosome 21, rather than two). Trisomy has been determined to be a function of maternal age.
An example of monosomy is Turner syndrome, where the individual is born with only one sex chromosome, an X.
Structural abnormalities
When the chromosome's structure is altered, this can take several forms:[3]
- Deletions: A portion of the chromosome is missing or deleted. Known disorders in humans include Wolf-Hirschhorn syndrome, which is caused by partial deletion of the short arm of chromosome 4; and Jacobsen syndrome, also called the terminal 11q deletion disorder.
- Duplications: A portion of the chromosome is duplicated, resulting in extra genetic material. Known human disorders include Charcot-Marie-Tooth disease type 1A, which may be caused by duplication of the gene encoding peripheral myelin protein 22 (PMP22) on chromosome 17.
- Translocations: A portion of one chromosome is transferred to another chromosome. There are two main types of translocations:
- Reciprocal translocation: Segments from two different chromosomes have been exchanged.
- Robertsonian translocation: An entire chromosome has attached to another at the centromere - in humans these only occur with chromosomes 13, 14, 15, 21, and 22.
- Inversions: A portion of the chromosome has broken off, turned upside down, and reattached, therefore the genetic material is inverted.
- Insertions: A portion of one chromosome has been deleted from its normal place and inserted into another chromosome.
- Rings: A portion of a chromosome has broken off and formed a circle or ring. This can happen with or without loss of genetic material.
- Isochromosome: Formed by the mirror image copy of a chromosome segment including the centromere.
Chromosome instability syndromes are a group of disorders characterized by chromosomal instability and breakage. They often lead to an increased tendency to develop certain types of malignancies.
Inheritance
Most chromosome abnormalities occur as an accident in the egg cell or sperm, and therefore the anomaly is present in every cell of the body. Some anomalies, however, can happen after conception, resulting in Mosaicism (where some cells have the anomaly and some do not). Chromosome anomalies can be inherited from a parent or be "de novo". This is why chromosome studies are often performed on parents when a child is found to have an anomaly. If the parents do not possess the abnormality it was not initially inherited; however it may be transmitted to subsequent generations.
Acquired chromosome abnormalities
Most cancers, if not all, carry chromosome abnormalities,[4] with either the formation of hybrid genes and fusion proteins, deregulation of genes and overexpresson of proteins, or loss of tumor supressor genes (see the "Mitelman Database" [5] and the Atlas of Genetics and Cytogenetics in Oncology and Haematology,[6]).
See also
Main article: List of genetic disorders
References
- ^ NHGRI. 2006. Chromosome Abnormalities
- ^ Rieger, R.; Michaelis, A.; Green, M.M. (1968). "Mutation". A glossary of genetics and cytogenetics: Classical and molecular. New York: Springer-Verlag. ISBN 9780387076683.
- ^ http://atlasgeneticsoncology.org/Educ/PolyMecaEng.html
- ^ http://atlasgeneticsoncology.org/Educ/Hempat_e.html
- ^ "Mitelman Database of Chromosome Aberrations and Gene Fusions in Cancer".
- ^ "Atlas of Genetics and Cytogenetics in Oncology and Haematology". atlasgeneticsoncology.org.
External links
- Chromosome disorders at the US National Library of Medicine Medical Subject Headings (MeSH)
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Chromosome abnormalities (Q90–Q99, 758)
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| Autosomal |
| Trisomies |
- Down syndrome
- Edwards syndrome
- Patau syndrome
- Trisomy 9
- Warkany syndrome 2
- Cat eye syndrome/Trisomy 22
- Trisomy 16
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| Monosomies/deletions |
- 1q21.1 deletion syndrome/1q21.1 duplication syndrome/TAR syndrome
- Wolf–Hirschhorn syndrome
- Cri du chat/Chromosome 5q deletion syndrome
- Williams syndrome
- Jacobsen syndrome
- Miller–Dieker syndrome/Smith–Magenis syndrome
- DiGeorge syndrome
- 22q11.2 distal deletion syndrome
- 22q13 deletion syndrome
- genomic imprinting
- Angelman syndrome/Prader–Willi syndrome (15)
- Distal 18q-/Proximal 18q-
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| X/Y linked |
| Monosomy |
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Trisomy/tetrasomy,
other karyotypes/mosaics |
- Klinefelter syndrome (47,XXY)
- 48,XXYY
- 48,XXXY
- 49,XXXYY
- 49,XXXXY
- Triple X syndrome (47,XXX)
- 48,XXXX
- 49,XXXXX
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| Translocations |
| Leukemia/lymphoma |
| Lymphoid |
- Burkitt's lymphoma t(8 MYC;14 IGH)
- Follicular lymphoma t(14 IGH;18 BCL2)
- Mantle cell lymphoma/Multiple myeloma t(11 CCND1:14 IGH)
- Anaplastic large cell lymphoma t(2 ALK;5 NPM1)
- Acute lymphoblastic leukemia
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| Myeloid |
- Philadelphia chromosome t(9 ABL; 22 BCR)
- Acute myeloblastic leukemia with maturation t(8 RUNX1T1;21 RUNX1)
- Acute promyelocytic leukemia t(15 PML,17 RARA)
- Acute megakaryoblastic leukemia t(1 RBM15;22 MKL1)
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| Other |
- Ewing's sarcoma t(11 FLI1; 22 EWS)
- Synovial sarcoma t(x SYT;18 SSX)
- Dermatofibrosarcoma protuberans t(17 COL1A1;22 PDGFB)
- Myxoid liposarcoma t(12 DDIT3; 16 FUS)
- Desmoplastic small round cell tumor t(11 WT1; 22 EWS)
- Alveolar rhabdomyosarcoma t(2 PAX3; 13 FOXO1) t (1 PAX7; 13 FOXO1)
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| Other |
- Fragile X syndrome
- Uniparental disomy
- XX male syndrome
- Ring chromosome (13; 14; 15; 20)
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Index of developmental medicine
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| Description |
- Embryology
- Cell lines
- endoderm
- mesoderm
- ectoderm
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| Disease |
- Due to toxins
- Syndromes
- Chromosomal
- Neonate
- Twins
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Mutation
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| Mechanisms of mutation |
- Insertion
- Deletion
- Substitution
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| Mutation with respect to structure |
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Point mutation
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- Nonsense mutation
- Missense mutation
- Silent mutation
- Frameshift mutation
- Dynamic mutation
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Large-scale mutation
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- Chromosomal translocations
- Chromosomal inversions
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| Mutation with respect to overall fitness |
- Deleterious mutation
- Advantageous mutation
- Neutral mutation
- Nearly neutral mutation
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