Review Question - QID 212631

A 2-year-old boy is brought to his pediatrician by his parents for a routine visit. Since his 18-month visit, the parents have become concerned that his speech does not seem to be developing appropriately. The parents report that the patient’s vocabulary is still limited to fewer than 10 words, and he is still only using single words to describe things. The parents say that his motor milestones do not seem to be affected, as the patient is very physically active and can run and kick a ball. At times the patient seems hyperactive and can be difficult to redirect. On exam, his temperature is 98.4°F (36.9°C), blood pressure is 110/70 mmHg, pulse is 80/min, and respirations are 14/min. The rest of the exam is unremarkable, except that the patient’s face appears to be abnormally long and narrow. The patient is further referred to a geneticist, as he is believed to have a trinucleotide repeat disorder. Which of the following is the most likely inheritance pattern of this disorder?