Increased methotrexate-induced chromosome breakage in patients with free trisomy 21 and their parents.

Increased susceptibility of chromosomes from peripheral blood lymphocytes to the antimetabolite methotrexate (2 X 10(-6) M) has been found in patients with free trisomy 21 and their parents (N = 14). The level of induced chromatid and chromosome breaks is lowest in normal controls intermediate in patients' mothers and fathers, and highest in trisomy 21 patients. The findings are viewed as a special type of cytogenetic polymorphism or as a defective chromosomal infrastructure, also in the parents of trisomic children.