A case of complete tetrasomy 12p versus mosaic tetrasomy 12p (Pallister-Killian syndrome). M.C. Lowery^1,2, R.L. Young², A. Li¹, M. Fowler¹, L.A. Prouty², M. Lucas³, H. Chen². 1) Dept. Pathology; 2) Dept. Pediatrics; 3) Dept. Obstetrics & Gynecology, Louisiana State Univ Health Sciences Center, Shreveport, LA.
   Pallister-Killian syndrome, or mosaic tetrasomy 12p, is a relatively rare syndrome that is clinically manifested by profound mental deficiency and multiple congenital anomalies. The syndrome exhibits tissue-specific mosaicism where a supernumerary isochromosome 12p is marked in fibroblasts but virtually absent in peripheral blood. Very few cases, if any, show total tetrasomy 12p. We report an isolated clinical case of a 18 year-old prima gravida who presented to the hospital in labor. Prenatal ultrasound revealed polyhydramnios, diaphragmatic hernia, short limbs, and short neck. Although the possibility of Pallister-Killian was suspected, amniocentesis was not performed because of late gestation and the patient being in labor. At birth, the infant was found to have hypertelorism, short neck, short limbs, and diaphragmatic hernia. In spite of resuscitation, the infant expired and an autopsy was performed. Death was attributed to pulmonary hypoplasia secondary to diaphragmatic hernia. Cytogenetic analysis on tissue from the infant revealed all cells with i(12p). Fluorescence in situ hybridization (FISH) was performed using a pericentromeric probe (CEP12/SpectrumOrange, Vysis) and a whole chromosome paint probe (WCP/SpectrumOrange, Vysis) for chromosome 12. FISH confirmed 4 copies of the chromosome 12 centromeric region in all interphase and metaphase cells analyzed. WCP analysis confirmed that structurally the der(12) was comprised of all 12 material. This case documents complete tetrasomy of 12p and that survival to term is possible.