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Detailed information of TRISOMY 18 SYNDROME
- 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:
- 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:
- 90% of cases
- due to meiotic nondisjunction
- less than 1% recurrence rate
2. Mosaicism
- 10% of cases
- due to postzygotic (postfertilization) mitotic
nondisjunction
- leads to the partial clinical expression of Trisomy 18
with a longer survival
3. 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 -> ½:
- partial clinical picture of trisomy 18 with a longer
survival and less profound mental retardation
CLINICAL FEATURES:
- 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
2. Organ Malformations
- severe mental retardation
- hypotonia -> hypertonia
- neural tube defects
- poor suck and weak cry
- failure to thrive
- ocular anomalies
2. Respiratory
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:
- to rule out organ malformations:
- cardiovascular anomalies - Echo
- gastrointestinal anomalies - Barium Swallow, Endoscope
- genitourinary anomalies - Ultrasound
2. Karyotyping
MANAGEMENT:
- very poor prognosis with:
- 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
INTERNET LINKS:
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Pediatric Database - TRISOMY 18 SYNDROME
Pediatric Organization - Pedbase [at] Gmail.com