Familial partial distal 18q (18q22-18q23) trisomy.

Three siblings were found to have partial trisomy of the distal portion of the long arm of chromosome 18 (18q22-18q23). This partial 18qter trisomy is the unbalanced product of a maternal 6p/18q trisomy with insertion of the distal portion of 18q(18q22-18q23) into band 6p11. The available data on the different partial trisomies of chromosome 18 are briefly reviewed.