Trisomy 18
Embryology - 26 Apr 2024 Expand to Translate |
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Introduction
(Edwards Syndrome, 18T) An aneuploidy, first recognized as a specific clinical entity by the discovery of an extra chromosome 18 in babies with a particular pattern of malformation by independent groups.[1] [2] [3]
In many cases associated abnormalities include: fetal growth restriction, polyhydramnios and congenital heart defects.
Both trisomy 13 and trisomy 18 are generally considered fatal anomalies, with a majority of infants dying in the first year after birth[4], see also the recent Japanese study.[5]
International Classification of Diseases: Q91 Edwards' syndrome and Patau's syndrome
Some Recent Findings
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More recent papers |
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This table allows an automated computer search of the external PubMed database using the listed "Search term" text link.
More? References | Discussion Page | Journal Searches | 2019 References | 2020 References Search term: Trisomy 18 <pubmed limit=5>Trisomy 18</pubmed> |
Survival Rate
Stillbirths occurs prenatally in 40% cases with fetal demise also before onset and during labor.
From a Japanese study of 73 live-born infants[5]
Time | Percentage |
---|---|
24 h | 63% |
1 week | 43% |
1 month | 33% |
1 year | 3% |
Prevalence
Abnormalities from USA Nationwide Inpatient Sample database (1998 to 2008)[8]
Features
Frequency | Organ/System | Prevalent type of malformation |
---|---|---|
Common (>75%) | heart | septal defects, patent ductus arteriosus, and polyvalvular disease |
Frequent (25-75%) | genitourinary | horseshoe kidney |
Less frequent (5-25%) | gastrointestinal
central nervous system craniofacial eye limb |
omphalocele, esophageal atresia with tracheo-esophageal fistula, pyloric stenosis, Meckel diverticulum
cerebellar hypoplasia, agenesis of corpus callosum, polymicrogyria, spina bifida orofacial clefts microphthalmia, coloboma, cataract, corneal opacities radial aplasia/hypoplasia |
Table modified from[6]
Pedbase Entry
Definition
A chromosomal disorder resulting in a syndrome characterized by specific (small) dysmorphic features and organ malformations.
Epidemiology
incidence: 1/8000 live births most die in embryonic or fetal life 2nd most common autosomal aberration 2nd most common multiple malformation syndrome age of onset: newborn risk factors: advanced maternal age F > M (4:1)
History
1960 first recognized as a specific clinical entity by the discovery of an extra chromosome 18 in babies with a particular pattern of malformation by three independent groups (Edwards et al., Patau et al., Smith et al.)
Pathogenesis - Genetics
Trisomy 18
90% of cases due to meiotic nondisjunction less than 1% recurrence rate
Mosaicism
10% of cases due to postzygotic (postfertilization) mitotic nondisjunction leads to the partial clinical expression of Trisomy 18 with a longer survival
Translocations
very rare give rise to partial trisomy 18 syndromes short arm: causes non-specific clinical features with mild or no mental deficiency long arm: entire: clinically indistinguishable from trisomy 18 distal 1/3 -> : partial clinical picture of trisomy 18 with a longer survival and less profound mental retardation
Clinical Features
Dysmorphic Features
1. Facial
- microcephaly with prominent occiput
- narrow bifrontal diameter
- short palpabral fissures
- low-set malformed ears
- cleft lip +/- palate
- narrow palatal arch
- micrognathia
2. Skeletal
- neck - webbed
- chest - short sternum, widely spaced nipples
- hips - small pelvis, congenital dislocation of the hips, limited hip abduction
- extremities - phocomelia, rockerbottom feet or equinovarus, short dorsiflexed big toes, fixed flexion deformity of the fingers (overlapping of the 2nd and 5th fingers over the 3rd and 4th fingers), simple arch pattern of the fingers and toes, hypoplasia of fingernails, single crease of 5th finger or all fingers (absence of interphalangeal flexion creases), simian crease
Organ Malformations
1. Central Nervous System
- severe mental retardation
- hypotonia -> hypertonia
- neural tube defects
- poor suck and weak cry
- failure to thrive
- ocular anomalies
2. Respiratory
- apnea
3. Cardiovascular( >95%)
- major: VSD, ASD, PDA
- minor: transposition, ToF, coarctation, anomalous coronary artery, dextrocardia, aberrant subclavian artery, arteriosclerosis, PS, bicuspid aortic and/or pulmonic valves
4. Gastrointestinal
- inguinal, umbilical, and/or diaphragmatic hernia
- congenital defects: diastasis recti, heterotopic pancreas, malrotation, Meckel's, tracheoesophageal fistula
5. Genitourinary
- cryptorchidism
- congenital defects: double ureter, ectopic kidney, horseshoe kidney, hydronephrosis, polycystic kidney
Investigations
Imaging Studies
- to rule out organ malformations:
- cardiovascular anomalies - Echo
- gastrointestinal anomalies - Barium Swallow, Endoscope
- genitourinary anomalies - Ultrasound
Karyotyping
Management
Supportive, very poor prognosis.
- 30% dying by 1 month of age
- 50% dying by 2 months of age
- 90% dying by 12 months of age
Genetic counselling, recurrence rate depends on genotype.
(modified from original 1999 Pedbase entry)
References
Reviews
<pubmed></pubmed> <pubmed></pubmed> <pubmed></pubmed> <pubmed>23088440</pubmed>
Articles
Search Pubmed
Search Pubmed: trisomy 13 | Edwards Syndrome
External Links
External Links Notice - The dynamic nature of the internet may mean that some of these listed links may no longer function. If the link no longer works search the web with the link text or name. Links to any external commercial sites are provided for information purposes only and should never be considered an endorsement. UNSW Embryology is provided as an educational resource with no clinical information or commercial affiliation.
- Medlineplus - Trisomy 18
- Trisomy 18 Organization
- Better Health Victoria - trisomy disorders
- SOFT USA Support Organization For Trisomy 18, 13, and Related Disorders
- SOFT UK Support Organisation for trisomy 13/18 and related disorders
- Trisomy 18 Support Program
- The Chromosome 18 Registry & Research Society
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Cite this page: Hill, M.A. (2024, April 26) Embryology Trisomy 18. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Trisomy_18
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G