The trisomy 12p syndrome is rare and may be caused by a number of chromosomal abnormalities.


The trisomy affects the short (p) arm of chromosome 12. This may entail:

(1) pure trisomy (incomplete or complete)

(2) mosaic trisomy

(3) other chromosomal abnormality


Rauch et al determined that smallest of duplications of (a) p13.2 to pter and (b) 12p13.1 to p13.33 produce the syndrome.


Dysmorphic facial features:

(1) macrocephaly

(2) flat face

(3) high forehead

(4) prominent cheeks

(5) large philtrum

(6) short nose with anteverted nostrils

(7) broad everted lower lip

(8) variable abnormalities of hair growth


Additional features:

(1) macrosomia at birth (heavy birth weight)

(2) muscular hypotonia

(3) developmental delay or mental retardation

(4) seizure disorder

(5) variable behavioral problems

(6) variable sleep disturbances

(7) variable polydactyly

(8) accessory nipples


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