Seizures and Cardiomyopathy in a Patient with Pallister-Killian Syndrome due to Hexasomy 12p Mosaicism

Pallister-Killian syndrome (PKS) is a rare disorder presenting with developmental delay, numerous dysmorphic features, and skin pigmentation anomalies. It is caused by mosaic tetrasomy of the short arm of chromosome 12. In most instances, tetrasomy is due to a supernumerary isochromosome i(12)(p10). Although mitotic instability is a generally accepted behavior for supernumerary chromosomes, hexasomy 12p due to a gain of an isochromosome 12p, has been hardly ever reported. We report a 10 year follow-up on a girl with 2 copies of isochromosome consisting of the short arm of chromosome 12, who has craniofacial features seen in PKS, such as sparse hair with an unusual pattern, sparse eyebrows, lacrimal duct stenosis, submucous cleft palate, Pallister lip (a relatively long philtrum continuing into the vermillion border of the upper lip), narrow palate, and wide alveolar ridges. She also has other abnormalities, including unilateral renal dysgenesis, rectovaginal fistula, pre-axial polydactyly of the right hand, severe global developmental delay, and hypotonia as well as some features suggestive of mosaicism such as bilateral asymmetry, patchy areas of rough skin, and retinal mottling. Initial cytogenetic studies from peripheral blood showed a normal female karyotype. Further cytogenetic studies on a skin biopsy showed mosaicism with 2 copies of the supernumerary isochromosome 12p.