weight loss, changes in mood, or changes in her appetite. She mentions that her mother told her about mild birth defects, but she cannot

recall the specifics. Past medical history and family history are benign. On physical examination, the patient is short in stature, has

a short and webbed neck and wide chest. Staining of buccal smear reveals absence of Barr bodies in the nucleus of epithelial cells. A

urine pregnancy test is negative. Which of the following genetic disorders is the most likely cause of this patient᾽s condition?