Trisomy 18: Difference between revisions
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'''Search Pubmed:''' [http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=search&term=trisomy%2013 trisomy 13] | [http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=search&term=Edwards%20Syndrome Edwards Syndrome] | |||
==External Links== | ==External Links== |
Revision as of 01:35, 19 November 2010
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]
- Links: Human Abnormal Development | Original Page
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
Articles
Search Pubmed
Search Pubmed: trisomy 13 | Edwards Syndrome
External Links
- 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