Double autosomal trisomy and mosaicism for chromosomes no. 8 and no. 21.

This patient was found to have a previously unreported double trisomy for chromosomes No. 8 and No. 21. She was recognized to have Down's syndrome at birth, and her subsequent development was consistent with that diagnosis. Her general health was good and there were no features suggesting an additional chromosomal abnormality. At this time there is no clearly recognized phenotype associated with trisomy 8. Two non-disjunctional events, occurring in meiosis and/or post-zygotic mitosis, are possible explanations of the chromosomal abnormalities found in this patient.