Reuters News Service, July 24, 2007 BOSTON - A woman seeking a tax write-off for her sex-change operation told the opening session of a potentially precedent-setting trial on Tuesday that the procedure was not just cosmetic but had made her whole. Rhiannon O'Donnabhain is challenging a decision by U.S. tax authorities not to allow the $25,000 cost of her 2001 sex-change and breast augmentation surgeries as a tax deduction. The Internal Revenue Service calls the procedures elective and cosmetic, and ineligible for a tax break. If the U.S. Tax Court in Boston overturns the IRS's decision, it could have big implications for transsexuals and other transgender people by setting a precedent for those who want to write off. Walter Meyer, a professor of psychiatry at the University of Texas Medical Branch and an expert in the field of gender identity disorder, told Reuters that in 2006 such disorders affected about one in 10,000 people.