Trisomy 18

Incidence

 * 1/6,000 - 1/8,000 live births
 * 4F:1M (more prevalent in females)

Molecular Etiology

 * 90% Trisomy 18
 * Maternal Meiosis Error = 90%


 * 10% mosaic with variable phenotype
 * Rarely Partial Trisomy
 * due to unbalanced translocation
 * partial q arm = indistinguishable from full trisomy

Associated Birth Defects

 * Cardiac Defects
 * Renal
 * Short sternum

Facial Features

 * microcephaly
 * prominent occiput
 * microopthalmia
 * low-set ears
 * microstomia
 * micrognathia

Extremities

 * clenched hands
 * rocker-bottom feet
 * flexed great toe
 * hypoplastic dermal ridges
 * contractures

Endocrine/Growth

 * severe IUGR
 * post-natal growth retardation

Neurological

 * hypertonia
 * Developmental Delay
 * Intellectual Disability (severe)

Prognosis

 * High Mortality
 * <1 week = 50%
 * <1 year = 90%
 * 1 year+ = 5-10%


 * COD: Usually aspiration and/or respiratory insufficiency

Recurrence Risks

 * Trisomy 18 = <1%
 * Partial Trisomy = depends on etiology