A cascade of chromosomal aberrations in three generations: a fragile 16q, an extra fragment and a rearranged 20.

The propositus' grandmother has a fragile 16q and belongs to a large family where several abortions and congenital anomalies were recorded. The portion distal to the fragile site was inherited as an extra fragment by the proposius' father who has it in 11% of his lymphocyte metaphases. This phenotypically harmless fragment has a high affinity for satellited chromosomes and was probably a main factor in the causation of the rearrangement that produced the partial trisomy 20p found in the propositus.