Trisomy 13 (Patau)

• 45 % die in first month
• 95% die by one year of age
• Few survive beyond 5 years

Genetics

• 75-80% are simple trisomies
• 20% have translocations
• a few cases are mosaic
• Risk of recurrence after one affected child with a standard trisomy is 1% to get another baby with some form of trisomy (trisomy 21 would be the most common)

Characteristics

• General: mental retardation, FTT
• Head: Forehead hemangiomas, Microcephaly, Severe CNS malformations (i.e. holoprosencephaly), Skin defects of posterior scalp (aplasia cutis), low hairline
• Face: Micro-ophthalmia w/ closely spaced eyes; Cleft lip and palate
• Congenital heart disease; Renal anomalies
• Polydactyly, rocker bottom feet

Some differences between Trisomy 13 and 18

• Both can have rocker bottom feet.
• 18 is hypertonic
• Head: 18 has micrognathia, prominent occiput. 13 has aplasia cutis and low hairline (low hairline also in Turner syndrome)
• Hands: 18 has nail hypoplasia, index and pinky fingers overlap the middle two (mnemonic: 18 year old showing funky gang sign); 13 has polydactyly (mnemonic: gang sign holding up 13 fingers)

Trisomy 18 (Edwards)
Trisomy 21 (Down)

CHLA board review course 2005
Baraitser and Winter, 1996. Color Atlas of Congenital Malformation Syndromes