Supernumerary small chromosomal anomaly: report of three cases including one with a familial inversion of chromosome 5.

Three cases of a small supernumerary chromosomal anomaly of essentially unknown origin associated with wide variability of clinical expression are reported. Case II has, in addition, a pericentric inversion of chromosome 5, which enables us to propose a mechanism, involving an unsuccessful crossing over, for the origin of the supernumerary chromosome.