TRISOMY 13 SYNDROME
 
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TRISOMY 13 SYNDROME

 

DEFINITION:

A chromosomal disorder resulting in a syndrome characterized by specific (midline) dysmorphic features and organ malformations.

EPIDEMIOLOGY:

  • incidence: 1/4000-10,000 live births
  • age of onset:
    • newborn
  • risk factors:
    • advanced maternal age
    • M = F

HISTORY:

  • 1657
    • first described by Bartholin
  • 1960
    • first recognized as a clinical syndrome when the trisomy etiology is discovered by Patau

PATHOGENESIS:

1. Genetics

1. Trisomy 13

  • 75% of cases
  • due to meiotic nondisjunction
  • recurrence rate: 1/4000

2. Translocations

  • 20% of cases
  • ¾ of these are due to de novo; recurrence rate: 1/4000
  • ¼ of these are due to familial translocation with a recurrence rate of 5-15%

3. Mosaicism

  • 5% of cases
  • due to postzygotic (postfertilization) mitotic nondisjunction
  • recurrence rate: 1/4000
  • usually less severe than full trisomy 13 but quite variable from full trisomy 13 to near-normal phenotype
  • survival usually longer with variable MR

2. Pathogenesis

  • a single defect during the first 3 weeks of development of the prechordal mesoderm can lead to morphologic defects of the midface, eyes, and forebrain and induction defects on the prosencephalon (cerebral hemispheres, diencephalon, hypothalamus, thalamus) -> holoprosencephaly

CLINICAL FEATURES:

1. Dysmorphic Features

1. Facial

  • microcephaly* with sloping forehead
  • wide sagittal sutures and fontanelles
  • aplasia cutis congenita
  • eyes - microphthalmia or anophthalmia
    • colobomata of iris (congenital fissure or gap)
    • retinal dysplasia
  • mouth - cleft lip* (60-80%) +/- palate
  • ears - abnormal helices +/- low set ears
    • deafness (sensorineuronal, conductive),
    • recurrent otitis media

2. Skeletal

  • thin posterior ribs +/- missing rib
  • hypoplasia of pelvis with shallow acetabular angle
  • extremities:
    • simian crease
    • distal palmar axial triradii
    • hyperconvex narrow fingernails
    • flexion of fingers +/- overlap
    • camptodactyly (permanent irreducible flexion)
    • polydactyly* of hands +/- feet
    • posterior prominence of heel*

2. Organ Malformations

1. Central Nervous System

  • holoprosencephaly (lack of septation of the forebrain) with incomplete development of the forebrain and the olfactory and optic nerves
  • apneic spells (central)
  • seizures
  • severe mental retardation

2. Cardiovascular

  • coarctation, ASD, PDA, VSD, dextroposition

3. Gastrointestinal

  • inguinal or umbilical hernia
  • omphalocele

4. Genitourinary

  • males: cryptorchidism, abnormal scrotum, ambiguous genitalia
  • females: bicornuate uterus
  • polycystic kidneys

5. Skin

  • aplasia cutis congenita
  • capillary hemangiomata (forehead)
  • loose skin, posterior neck

     

    *major features

3. Partial Trisomy (proximal segment)

  • nonspecific clinical pattern:
    • large nose
    • short upper lip
    • receding mandible
    • severe mental retardation
    • 5th finger clinodectyly
  • little similarity to full trisomy 13
  • survival not significantly reduced

4. Partial Trisomy (distal segment)

  • specific clinical pattern:
    • bushy eyebrows with long incurved lashes
    • frontal capillary hemangiomata
    • short nose with upturned tip
    • prominent antihelix
    • elongated philtrum
    • severe mental retardation
    • synophrys
  • ¼ of patients die during early postnatal life

INVESTIGATIONS:

1. Imaging Studies

  • to rule out organ malformations:
    • cardiovascular anomalies - Echo
    • central nervous system anomalies - CT/MRI
    • genitourinary anomalies - Ultrasound

2. EEG

  • hypsarrhythmia

3. Karyotyping

MANAGEMENT:

1. Supportive

  • very poor prognosis with:
    • 45% dying by 1 month
    • 69% dying by 6 months
    • 72% dying by 12 months
  • genetic counselling
    • recurrence rate depends on genotype

INTERNET LINKS:

Support Organization for Trisomy 18, 13, and Related Disorders
 

 

Pediatric Database - TRISOMY 13 SYNDROME

 

Pediatric Organization - Pedbase [at] Gmail.com

 
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