Tetrasomy 12p (Pallister-Killian syndrome) is a rare disorder that can be a challenge to diagnose.


Synonyms: Pallister mosaic syndrome, Pallister-Killian-Teschler-Nicola Syndrome


Genetic defect: mosaic tetrasomy (non-mosaic tetrasomy fatal in utero). Demonstration of the extra chromosomes depends on the cells cultured with the highest rate in amniocytes and bone marrow cells and the lowest rate in lymphocytes.


Common clinical features:

(1) coarse facisl features with frontal bossing, low set and dysplastic ears, hypertelorism, wide nasal bridge, exophthalmos, shallow upper orbital ridges, upward slanting palpebral fissues, inner epicanthic folds, small and upturned nares, long philtrum with prominent upper lip)

(2) pigmentary skin anomalies (hyperpigmentation, hypopigmentation)

(3) abnormalities in hair distribution (high frontal hairline, temporofrontal alopecia, abnormal eyebrows and eyelashes)

(4) profound mental retardation

(5) seizures

(6) diaphragmatic defect

(7) accessory nipples


Variable findings:

(1) disproportionate shortness of extremities

(2) small and broad hands and feet

(3) postaxial polydactyly

(4) microphthalmia

(5) other ocular abnormalities (cataract, keratoconus, pinpoint pupils. etc)

(6) congenital heart disease

(7) anal atresia or stenosis

(8) renal malformations

(9) genital abnormalities (cryptorchidism, ambiguous external genitalia, other)

(10) rhizomelic brachymelia

(11) other skeletal malformations (atlanto-occipital fusion, absence of twelfth pair of ribs)

(12) hypotonia

(13) absence of one umbilical artery

(14) large and protruding tongue occurs over time

(15) large and protruding mandible occurs over time


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