(Corrects share price movement in paragraph 6)

March 10 (Reuters) - The U.S. Food and Drug Administration approved Acadia Pharmaceuticals Inc's drug for the treatment of Rett syndrome, a genetic brain disorder, the company said on Friday, making it the first-approved drug for the condition.

The U.S. health regulator's decision allows use of the drug, to be sold under the brand name Daybue, in adult and pediatric patients two years of age and older and comes with a warning of diarrhea and weight loss.

Acadia said it plans to make the drug available to patients by the end of April. It, however, did not disclose the details of the drug price. The approval comes months after the regulator declined to approve expanded use of its drug Nuplazid to treat psychosis related to Alzheimer's disease. Analysts have said approval of Daybue would help drive growth for the company in the near term.

Rett's syndrome is a rare neurodevelopmental condition that occurs primarily in girls. According to government estimates, it affects fewer than 50,000 people in the U.S.

Shares of the California-based company closed 0.68% lower on Friday. (Reporting by Bhanvi Satija, Nandhini Srinivasan and Anirudh Saligrama in Bengaluru; Editing by Shailesh Kuber and William Mallard)