Trisomy 20 mosaicism in two unrelated girls with skin hypopigmentation andnormal intellectual development

The prenatal diagnosis of trisomy 20 mosaicism presents a challenge for pra ctitioners and parents. The diagnosis implies an uncertain risk for an inco nsistent set of physical and developmental findings, as well as a substanti al chance for a child that is normal physically and developmentally, We rep ort two girls (ages nine years one month and eight years one month) with no rmal intelligence and hypopigmented skin areas. Both girls were born after a prenatal diagnosis of trisomy 20 mosaicism in amniocytes, Case 1 had 83% and 57% trisomy 20 cells from two separate amniocenteses and Case 2 had 90% trisomy 20 cells from an amniocentesis. Trisomy 20 was confirmed after bir th in urinary sediment (25%) and chorionic villus cells (15%) in Case 1, wh ile cord blood lymphocytes (30 cells) and skin fibroblasts (50 cells) had o nly 46,XX cells. Trisomy 20 was confirmed after birth in urinary sediment ( 100%), placenta (100%), cord (10%), amniotic membrane (50%), and skin fibro blasts (30%) in Case 2, while cord blood lymphocytes (100 cells) had only 4 6,XX cells. This is the first report of a hypopigmented pigmentary dysplasi a associated with isolated trisomy 20 mosaicism, Our patients are the oldes t reported children with trisomy 20 mosaicism confirmed after birth. (C) 20 01 Wiley-Liss,Inc.