Trisomy 18

Source: Wikipedia, the free encyclopedia.
Trisomy 18
Other namesTrisomy 18 (T18
Supportive care[2]
Prognosis5–10% survive past a year old[3]
Frequency1 per 5,000 births[3]

Trisomy 18, also known as Edwards syndrome, is a

small jaw, clenched fists with overlapping fingers, and severe intellectual disability
.

Most cases of trisomy 18 occur due to problems during the formation of the

ultrasound during pregnancy can increase suspicion for the condition, which can be confirmed by amniocentesis.[2]

Treatment is

condition due to a third chromosome at birth, after Down syndrome for a third chromosome 21.[4]

Trisomy 18 occurs in around 1 in 5,000 live births.

John Hilton Edwards, who first described the syndrome in 1960.[5]

Signs and symptoms

Clenched hand and overlapping fingers: index finger overlaps third finger and fifth finger overlaps fourth finger, characteristically seen in trisomy 18. This is caused by congenital joint contracture.[6]

Children born with Edwards' syndrome may have some or all of these characteristics: kidney malformations, structural heart defects at birth (i.e.,

contractures at birth).[7][8]

Some physical malformations associated with Edwards' syndrome include small head (

undescended testicles.[7][8]

In utero, the most common characteristic is cardiac anomalies, followed by central nervous system anomalies such as head shape abnormalities. The most common intracranial anomaly is the presence of choroid plexus cysts, which are pockets of fluid on the brain. These are not problematic in themselves, but their presence may be a marker for trisomy 18.[9][10] Sometimes, excess amniotic fluid or polyhydramnios is exhibited.[7] Although uncommon in the syndrome, trisomy 18 causes a large portion of prenatally diagnosed cases of Dandy–Walker malformation.[11][12]

Genetics

Karyotype of a person with trisomy 18. Three copies of the Chromosome 18 are detected.

Trisomy 18 is a chromosomal abnormality characterized by the presence of an extra copy of genetic material on the 18th chromosome, either in whole (trisomy 18) or in part (such as due to translocations). The additional chromosome usually occurs before conception. The effects of the extra copy vary greatly, depending on the extent of the extra copy, genetic history, and chance. Trisomy 18 occurs in all human populations, but is more prevalent in female offspring.[13]

A typical egg or sperm cell contains individual chromosomes, each of which contributes to the 23 pairs of chromosomes needed to form a normal cell with a typical human

haploid number 24 rather than 23. Fertilization of eggs or insemination by sperm that contain an extra chromosome results in trisomy, or three copies of a chromosome rather than two.[14]

Trisomy 18 (47,XX,+18) is caused by a meiotic nondisjunction event. In nondisjunction, a pair of chromosomes fails to separate during cell division; thus, a gamete (i.e., a sperm or egg cell) is produced with an extra copy of chromosome (for a total of 24 chromosomes). When combined with a normal gamete from the other parent, the resulting embryo has 47 chromosomes, with three copies of the problematic chromosome (in this case, chromosome 18). (Although an embryo could inherit a trisomy from both parents, it is, as a rule, extremely rare, and worse in terms of clinical perspective and prognosis.)

A small percentage of cases occur when only some of the body's cells have an extra copy of chromosome 18, resulting in a mixed population of cells with a differing number of chromosomes. Such cases are sometimes called mosaic trisomy 18. Very rarely, a piece of chromosome 18 becomes attached to another chromosome (translocated) before or after conception. Affected individuals have two copies of chromosome 18 plus extra material from chromosome 18 attached to another chromosome. With a translocation, a person has a partial trisomy for chromosome 18, and the abnormalities are often less severe than for the typical trisomy 18.[15]

Diagnosis

Ultrasound can increase suspicion for the condition, which can be confirmed by CVS or amniocentesis.[2]

Levels of PAPP-A, AFP, and uE3 are generally decreased during pregnancy and free beta HCG which is elevated. [16]

Prognosis

About 95% of pregnancies that are affected do not result in a live birth.

better source needed] One percent of children live to age 10.[13] However, a retrospective Canadian study of 254 children with trisomy 18 demonstrated ten-year survival of 9.8%, and another found that 68.6% of children with surgical intervention survived infancy.[21] Though rare, some persons with Trisomy 18 do survive into their twenties and thirties.[22]

Epidemiology

Trisomy 18 occurs in about 1 in 5,000 live births, but more pregnancies are affected by the syndrome as the majority of those diagnosed with the condition prenatally will not survive to birth.[3] Although women in their 20s and early 30s may conceive babies with trisomy 18, the risk increases with age. The average maternal age for conceiving a child with this disorder is 32.5.[23]

History

Trisomy 18 was first identified by John Hilton Edwards in 1960, although he originally believed it to be caused by a trisomy of chromosome 17.[24] Klaus Patau and Eeva Therman reported another two cases shortly thereafter.[25] They identified the extra chromosome as being part of what Patau's lab called "group E", containing chromosomes 16, 17, and 18, but were unable to determine which chromosome was responsible at the time. Analyzing 5 more cases, they were able to determine that the extra chromosome was in fact chromosome 18.[26]

See also

  • 18q deletion syndrome

References

  1. ^ "Edwards' syndrome (T18): Information for parents". December 2020.
  2. ^ a b c d e f g h "Trisomy 18". Orphanet. May 2008. Archived from the original on 3 October 2016. Retrieved 1 October 2016.
  3. ^ a b c d e f g h i j k l m n o p q r s "trisomy 18". GHR. March 2012. Archived from the original on 2 October 2016. Retrieved 1 October 2016.
  4. ISBN 978-0323075763. Archived
    from the original on 2016-10-02.
  5. ^ "Edwards syndrome (John Hilton Edwards)". WhoNamedIt.com. Archived from the original on 2008-07-09. Retrieved 2008-07-24.
  6. PMID 23088440
    .
  7. ^ a b c "What is Trisomy 18?". Trisomy 18 Foundation. Archived from the original on 2009-03-23. Retrieved 2008-07-24.
  8. ^ a b "Trisomy 18". Medline. Archived from the original on 2008-10-01. Retrieved 2008-07-24.
  9. PMID 17357350
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  10. S2CID 23836946
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  11. S2CID 32024323
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  12. S2CID 20046766
    .
  13. ^ a b c d Chen, MD, Harold. "Introduction to Trisomy 18". EMedicine. Archived from the original on 2008-08-04. Retrieved 2008-07-24.
  14. ^ For a description of human karyotype see Mittleman, A., ed. (1995). "An International System for Human Cytogenetic Nomenclature". Archived from the original on 2006-07-07. Retrieved 2006-06-04.
  15. ^ "Edwards' syndrome (trisomy 18)". nhs.uk. 2017-10-18. Retrieved 2021-07-05.
  16. ^ "Prenatal Diagnose". Archived from the original on 2018-08-17. Retrieved 2018-08-17.
  17. ^ "Trisomy 18: MedlinePlus Medical Encyclopedia". Nlm.nih.gov. 2011-12-14. Archived from the original on 2012-01-21. Retrieved 2012-01-04.
  18. ISBN 0-443-05357-X.[permanent dead link
    ]
  19. ^ Zoler, Mitchel L. (March 1, 2003). "Trisomy 13 survival can exceed 1 year". OB/GYN News. Archived from the original on 2012-07-18. Retrieved 2008-07-24.
  20. ^ "Trisomy 13 survival can exceed 1 year | OB/GYN News". Find Articles. 2003-03-01. Archived from the original on 2012-02-21. Retrieved 2012-01-04.
  21. ^
    PMID 27458947. Archived
    from the original on 17 November 2016. Retrieved 3 December 2016.
  22. PMID 33297534
    .
  23. ^ "Prevalence and Incidence of Edwards Syndrome". Diseases Center-Edwards Syndrome. Adviware Pty Ltd. 2008-02-04. Archived from the original on 2004-06-25. Retrieved 2008-02-17. mean maternal age for this disorder is 32½
  24. PMID 13819419
    .
  25. PMID 13831938
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  26. S2CID 2105207
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External links
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