Trisomy 13

 

Epidemiology and Etiology:

    • Maternal nondisjunction (M1 usually)
    • ~20% due to unbalanced translocation
    • 1:15,000-20,000 births
    • risk factors:
      • advanced maternal age

 

Common sites:

    •  

 

Gross features:

    • growth retardation
    • microcephaly
    • wide open sutures
    • severe CNS malformations
      • arhinencephaly
      • holoprosencephaly
      • neural tube defects
    • facial appearance (most distinctive)
      • arhinencephaly
      • holoprosencephaly
      • sloping forehead
      • microphthalmia
      • iris coloboma
      • absence of eyes
      • malformed ears
      • cleft lip and cleft palate often
    • hands and feet
      • post-axial polydactyly
      • hands clench with 2nd and 5th digits overlapping the 3rd and 4th (same as trisomy 18)
      • rocker-bottom or club feet (same as trisomy 18)
      • simian creases often
    • heart malformations (usually)
      • VSD
      • PDA
    • Urogenital defects
      • Cryptorchidism
      • Bicornuate uterus
      • Hypoplastic ovaries
      • Polycystic kidneys

 

Histologic features:

    •  

 

Immunophenotype:

Marker:

Sensitivity:

Specificity:

 

 

 

 

Molecular features:

    •  

 

Other features:

    • clinical features:
      • severe mental retardation
    • ultrasound:
      • 90-100% detection rate
        • due to plethora of structural abnormalities
      • Holoprosencephaly
      • Microcephaly
      • Neural tube defects
      • Facial clefts
      • Ocular anomalies
      • Cardiac defects
      • Echogenic intracardiac focus
      • Cystic hygroma
      • Polydactyly
      • Polycystic kidneys
      • IUGR
      • club feet
    • prognosis:
      • half die within first month
    • recurrence risk:
      • < 2%, even if one parent is a carrier of the translocation

 

References:

    • Thompson & Thompson Genetics in Medicine (2007)
    • Evans MI, ed.  Prenatal Diagnosis (2006)