Developmental and learning disorders Quiz: Ace Your Exams

An 18-month-old girl is brought to the office by her parent for evaluation of “odd behaviors.” The patient has met all developmental and motor milestones over the past year, including walking and playing with toys. However, over the past four months, she has had difficulty walking and sitting up without support. In addition, while the patient used to babble and say single words, she has not spoken much for the past three months. Weight and height are at the 50th percentile. The patient’s head circumference has decreased from the 40th percentile to the 25th percentile in the past four months. Temperature is 37.0°C (98.6°F), blood pressure is 100/67 mmHg, and pulse is 103/min. On examination, the patient is hypotonic and needs to be held by her parent to sit upright. She wrings her hands together repeatedly. An underlying genetic disorder is suspected. Which of the following best describes the normal function of the protein produced by this gene?