A case of mosaic tetrasomy 12p (Pallister-Killian Syndrome) diagnosed prenatally: comparison of chromosome analyses of various cells obtained from the patient.

A pregnant woman was referred to our hospital at the 29th week of gestation with the symptom of polyhydramnios; diaphragmatic herniation of the fetus was suspected. Fetal chromosome anlaysis was performed using fibroblasts obtained by aminocentesis, and mosaicism of 46,XX and isochromosome of 12p were diagnosed. Out of 50 karyotyped cells, 19 (38.0%) showed the tetrasomy of the isochromosome of 12p. The mother vaginally delivered a baby girl who died just after delivery. The analysis of cord blood lymphocytes revealed only 0.5% incidence of tetrasomy of 12p. The incidence of tetrasomy was 8.0% for the placental chorionic villi, 48.0% for the fibroblasts obtained from the umbilical cord, and 70.0% for the skin fibroblasts. Thus, the diagnosis of Pallister-Killian Syndrome (PKS) is confirmed by mosaicism of i(12p), that is, the affected patients exhibit tissue-specific mosaicism, with the abnormal karyotype expression in limited lymphocytes, but marked in fibroblasts.