Mosaic Trisomy la Due to a de novo Translocation in a Foetus with Early Developmental Abnormalities (Karyotype 46,XY,der(14),t(1;14)(p11;p11.2)/46,XY) Delineation of Parent and Cell Stage of Origin

Pure trisomies of the whole long arm of chromosome I are extremely rare and have been reported only once in association with mosaicism. We report on a malformed foetus with mosaic trisomy 1 p 11 to 1 qter whose clinical features were partially in accordance with those of previously described trisomy 1q patients. An additional long arm of chromosome I was translocated onto 14p 11.2 (karyotype: mos46,XYder(14)t(1:14)(p11:p11.2)/46,XY). Mosaic formation of the partial trisomy I was investigated in seven different somatic tissues of first and second trimester pregnancy. The distribution of the pathologic cells was unequal, ranging from 4 to 93%. The duplicated region was paternal in origin. We were able to delineate two possible complex formation mechanisms involving paternal meiosis and postzygotic mitoses.