An estimated one-quarter to one-half percent of the American population is transsexual, however, Keisling said.

CNN: Sonny and Cher's child transitioning from female to male

Someone's decision to transition does not necessarily mean they are undergoing gender reassignment surgery, and in many cases they do not, said Mara Keisling, executive director of the Washington-based National Center for Transgender Equality.

CNN: Sonny and Cher's child transitioning from female to male