A 16-year-old girl is being evaluated in your office because she has not yet started menstruating. Her vision, hearing, and smell are normal. Her current medications include occasional ibuprofen for headaches. On examination, she is 5 feet 8 inches tall and weighs 154 lb. Her blood pressure is 110/70 mm Hg. She has Tanner stage 1 breast development and axillary and pubic hair pattern. The external genitalia appear as normal females. Mental examination is normal. She has an average IQ. Laboratory evaluation reveals a 46, XX karyotype, low follicle-stimulating hormone (FSH) and luteinizing hormone (LH), and absent GnRH. The urine pregnancy test is negative. What is the most likely cause of amenorrhea in this patient?
