Gene editing techniques may eventually allow trisomy to be treated at the cellular level, according to an in vitro proof-of-concept study. Down syndrome is caused by the presence of a third copy ...

"You either have XX or XY chromosomes," Rep. Nancy Mace, R-S.C., wrote Feb. 20 on X. "Those are the options." Most commonly, a person is born with two X chromosomes (female) or an X and a Y (male).