Karyotyping urine sediment cells confirms trisomy 12 mosaicism detected at amniocentesis

A newborn is described in whom trisomy 12 mosaicism was detected prenatally at third trimester amniocentesis during the fourth pregnancy of a 34-year-old woman. After birth, trisomy 12 cells were found in placental tissue and in cultured urine sediment cells. A sample of cord blood and a skin biopsy revealed only normal (46,XX) cells. Both parents had a normal karyotype. After a difficult start with unexplained hypoglycaemias and convulsion equivalents, the girl is doing well at the age of 9 months: there are no signs of central motor disturbance. The importance of the use of cultured urine sediment cells in confirming chromosomal mosaicism is stressed.