Trisomy 21

Incidence

 * 1/600 live births

Molecular Etiology

 * 95% Trisomy 21
 * 4% Translocation (75% de novo)
 * 1% Mosaic

Associated Birth Defects
Cardiac Defects Gastrointestinal Anomalies
 * A-V Canal / "Endocardial Cushion Defect" = 40%
 * Duodenal Atresia = 10-18%

Facial Features

 * flat face
 * macroglossia
 * upslanted eyes
 * epicanthal folds
 * small ears
 * low-set ears
 * brushfield spots

Extremities

 * brachydactyly
 * 5th finger clinodactyly(shortened middle phalanx)
 * single palmar crease (Simian crease)
 * sandal foot

Neurological

 * hypotonia
 * atlantoaxial instability = 10-20%
 * Intellectual Disability (average IQ ~50)
 * Early Onset Alzheimer's Disease

Endocrine

 * hypothyroidism

Sensorial

 * frequent otitis media
 * hearing loss
 * myopia
 * early cataracts

Malignancies

 * leukemia = 1% (acute myelogenous leukemia; AML)

Prognosis

 * Variable Phenotype
 * Many do well in supervised living situations; sheltered workshops
 * Living independently extremely uncommon
 * Parents should begin planning ahead

Recurrence Risks

 * Trisomy 21
 * <35 years = 1%
 * >(35)years = age related risk


 * Mosaic
 * <1%


 * Translocation
 * de novo = <1%
 * Familial (except 21;21)
 * 10-15% if maternal
 * 1% if paternal