Ring chromosome explained

A ring chromosome is an aberrant chromosome whose ends have fused together to form a ring. Ring chromosomes were first discovered by Lilian Vaughan Morgan in 1926.^[1] A ring chromosome is denoted by the symbol r in human genetics and R in Drosophila genetics. Ring chromosomes may form in cells following genetic damage by mutagens like radiation, but they may also arise spontaneously during development.

Formation

In order for a chromosome to form a ring, both ends of the chromosome are usually missing, enabling the broken ends to fuse together. In rare cases, the telomeres at the ends of a chromosome fuse without any loss of genetic material, which results in a normal phenotype.^[2]

Complex rearrangements, including segmental microdeletions and microduplications, have been seen in numerous ring chromosomes, providing important clues regarding the mechanisms of their formation.^[3]

Small supernumerary rings can also form, resulting in a partial trisomy.

Ring chromosomes are unstable during cell division and can form interlocking or fused rings.

Associated syndromes

Human genetic disorders can be caused by ring chromosome formation. Although ring chromosomes are very rare, they have been found in all human chromosomes. Symptoms seen in patients carrying ring chromosomes are more likely to be caused by the deletion of genes in the telomeric regions of affected chromosomes, rather than by the formation of a ring structure itself.^[4] Almost all ring chromosome syndromes feature marked growth delay.^[5]

Ring chromosomes can be inherited or sporadic. Mosaicism is common and affects the severity of the condition.^[4] Location of fusion also affects severity due to loss of differing amounts of genetic material from the ends of chromosomes.

Disorders arising from the formation of a ring chromosome include:

!Chromosome!Typical features!

Ring chromosome 1	microcephaly, facial abnormalities	^[6]
Ring chromosome 2	Small stature	^[7] ^[8]
Ring chromosome 3		^[9]
Ring chromosome 4	Craniofacial abnormalities	^[10]
Ring chromosome 5		^[11]
Ring chromosome 6	Microcephaly, facial abnormalities, hand abnormalities	^[12]
Ring chromosome 7	Craniofacial abnormalities, speech deficits	^[13]
Ring chromosome 8	Craniofacial abnormalities, hydronephrosis, hand abnormalities	^[14]
Ring chromosome 9	Delayed growth, abnormal facial features, low muscle tone	^[15]
Ring chromosome 10	delayed growth, facial dysmorphia, reproductive abnormalities	^[16]
Ring chromosome 11		^[17]
Ring chromosome 12	Delayed growth, abnormal facial features, microcephaly	^[18] ^[19]
Ring chromosome 13	Microcephaly, delayed growth, reproductive abnormalities	^[20]
Ring chromosome 14	Epilepsy,	^[21]
Ring chromosome 15	Growth delay, microcephaly, speech delay	^[22]
Ring chromosome 16	microcephaly, growth delay, facial abnormalities	^[23] ^[24]
Ring chromosome 17		^[25]
Ring chromosome 18	growth delay, facial abnormalities	^[26]
Ring chromosome 19		^[27]
Ring chromosome 20	Epilepsy, abnormal facial features, growth delay	^[28]
Ring chromosome 21	Short stature, microcephaly, reproductive abnormalities	^[29]
Ring chromosome 22	hypotonia, autistic-like behavior	^[30]
Ring chromosome X	Turner syndrome
Ring chromosome Y		^[31]

See also

• Chromosome abnormalities

External links

• Atlas of Genetics and Cytogenetics in Oncology and Haematology, explains HOW the ring formation causes abnormalities.

Notes and References

1. Morgan. LV. Correlation between Shape and Behavior of a Chromosome.. Proceedings of the National Academy of Sciences of the United States of America. Mar 1926. 12. 3. 180–1. 16576974. 1084483. 10.1073/pnas.12.3.180. free.
2. https://web.archive.org/web/20090629081619/http://humrep.oxfordjournals.org/cgi/reprint/20/2/462 Mitotic and meiotic behaviour of a naturally transmitted ring Y chromosome: reproductive risk evaluation
3. http://www.molecularcytogenetics.org/content/1/1/16 Shchelochkov O et al.
4. Nelson Textbook of Pediatrics, Chapter 81, 604-627 https://www.clinicalkey.com/#!/content/book/3-s2.0-B9781455775668000818?scrollTo=%23hl0003126
5. Yip. Moh-Ying. Autosomal ring chromosomes in human genetic disorders. 4729093. Translational Pediatrics. 164–174. 10.3978/j.issn.2224-4336.2015.03.04. 2015. 4. 2. 26835370.
6. Web site: Ring chromosome 1 - Genetic and Rare Diseases Information Center (GARD) – an NCATS Program. rarediseases.info.nih.gov. 2017-12-01. 2022-02-03. https://web.archive.org/web/20220203103610/https://rarediseases.info.nih.gov/diseases/1320/index. dead.
7. Web site: Orphanet: Ring chromosome 2 syndrome. www.orpha.net.
8. Web site: Ring 2. 2017-12-04. 2017-12-05. https://web.archive.org/web/20171205042222/http://www.rarechromo.org/information/Chromosome%20%202/Ring%202%20FTNW.pdf. dead.
9. Web site: Orphanet: Ring chromosome 3 syndrome. www.orpha.net.
10. Web site: Orphanet: Ring chromosome 4 syndrome. www.orpha.net.
11. Web site: Orphanet: Ring chromosome 5 syndrome. www.orpha.net.
12. Web site: Orphanet: Ring chromosome 6 syndrome. www.orpha.net.
13. Web site: Orphanet: Ring chromosome 7 syndrome. www.orpha.net.
14. Web site: Ring chromosome 8 - Genetic and Rare Diseases Information Center (GARD) – an NCATS Program. rarediseases.info.nih.gov.
15. Web site: Ring 9. 2017-12-04. 2016-04-18. https://web.archive.org/web/20160418051837/http://www.rarechromo.org/information/Chromosome%20%209/Ring%209%20FTNW.pdf. dead.
16. Web site: Orphanet: Ring chromosome 10 syndrome. www.orpha.net.
17. Web site: Ring chromosome 11 - Genetic and Rare Diseases Information Center (GARD) – an NCATS Program. rarediseases.info.nih.gov. 2017-12-01. 2022-02-03. https://web.archive.org/web/20220203103609/https://rarediseases.info.nih.gov/diseases/10846/index. dead.
18. Web site: Orphanet: Ring chromosome 12 syndrome. www.orpha.net.
19. Web site: Ring chromosome 12 Genetic and Rare Diseases Information Center (GARD) – an NCATS Program. rarediseases.info.nih.gov. en. 2017-12-04. 2022-02-03. https://web.archive.org/web/20220203103614/https://rarediseases.info.nih.gov/diseases/1325/index. dead.
20. Web site: Ring chromosome 13 Genetic and Rare Diseases Information Center (GARD) – an NCATS Program. rarediseases.info.nih.gov. en. 2017-12-04.
21. Web site: Orphanet: Ring chromosome 13 syndrome. www.orpha.net.
22. Web site: Ring 15. 2017-12-04. 2017-12-05. https://web.archive.org/web/20171205093014/http://www.rarechromo.org/information/Chromosome%2015/Ring%2015%20FTNW.pdf. dead.
23. Web site: Orphanet: Ring chromosome 16 syndrome. www.orpha.net.
24. Web site: Ring chromosome 16 Genetic and Rare Diseases Information Center (GARD) – an NCATS Program. rarediseases.info.nih.gov. en. 2017-12-04.
25. Web site: Orphanet: Ring chromosome 17 syndrome. www.orpha.net.
26. Web site: Orphanet: Ring chromosome 18 syndrome. www.orpha.net.
27. Web site: Orphanet: Ring chromosome 19 syndrome. www.orpha.net.
28. Web site: Ring chromosome 20 Genetic and Rare Diseases Information Center (GARD) – an NCATS Program. rarediseases.info.nih.gov. en. 2017-12-04.
29. Web site: Orphanet: Ring chromosome 21 syndrome. www.orpha.net.
30. Web site: Orphanet: Ring chromosome 22 syndrome. www.orpha.net.
31. Web site: Orphanet: Ring chromosome Y syndrome. www.orpha.net.