Variant chromosome 3 (inv3) in normal newborns and their parents, and in children with mental retardation.

The chromosomes of 102 normal newborn babies (51 boys and 51 girls) born at term, their parents, and 45 nonrelated children with mental retardation at the level of imbecility were investigated by fluorescence microscopy using propyl quinacrine mustard. In each of the 11 families, one of the parents had a variant chromosome 3 that was interpreted as resulting from a pericentric inversion of the brilliant band (or C band) only (inv3). In four cases inv3 was transmitted to the child. The frequency of inv3 in newborn boys and girls was 2 and 6% respectively, and in adult men and women 5 and 6% respectively. In children with mental retardation of unknown etiology the inv3 was detected in five cases (11.1%). This difference from normal persons was not significant.