Amniotic trisomy 11 mosaicism--is it a benign finding?

A case of prenatally diagnosed trisomy 11 mosaicism with a normal outcome is reported and the medical literature on prenatal detection of this finding is reviewed.

Proportion of cells with trisomy 11 was evaluated in amniocytes, fetal blood lymphocytes, newborn fibroblasts and urinary epithelial cells. Karyotype studies and fluorescence in situ hybridization analysis using the 11q13LS1 CCND1 probe were performed.

Trisomy 11 level III mosaicism of 26% was detected in amniotic fluid cells. Periumbilical blood sampling showed a normal fetal karyotype. No fetal structural abnormalities were noted on ultrasound scan. The infant was spontaneously delivered and had normal physical findings at birth. No evidence of trisomic cells was found on extensive postnatal evaluation, implying an extraembryonic origin. Molecular analysis excluded uniparental disomy of chromosome 11. At 1 year of age, the baby is developing normally.

Only three reports on trisomy 11 mosaicism identified at amniocentesis have been published previously, all with a normal outcome. Additional cases of prenatally diagnosed mosaicism for trisomy 11 are necessary to assess more accurately the clinical significance of this finding.