A case of r(21) with stigmata of atypical Down syndrome

A case of r(21) with stigmata of atypical Down syndrome is presented. Karyotype of the proposita was determined as 45,XX,-21/46,XX,-21,+r(21)/47,XX,-21,+r(21),+(21). Most ring chromosomes showed double-sized ring chromosomes, which were trisomic for 21p11-21q22.3 and monosomic for 21q22.3-qter. SOD-1 activity revealed only slight elevation. The mechanism of ring formation is discussed.