First report of mosaic trisomy 12 in a liveborn individual.

Trisomy 12 mosaicism was found in a 36-year-old woman with minor anomalies, neuromuscular abnormalities, and moderate mental retardation. Trisomy 12 was present in 13% of the lymphocytes but not in skin fibroblasts. Previous reports of dup (12p) and dup(12q) are reviewed. To our knowledge this is the first report of a "complete" trisomy 12 in a liveborn individual.