A 13-Year-Old Boy Is Evaluated for Abnormal Growth

A 13-year-old boy is evaluated for abnormal growth.  His mother says that he has grown rapidly over the past 10 months and is much taller than his older brother and other children his age.  During this time, she has had a hard time finding clothes that fit him and has had to buy new shoes for him each month due to increasing foot size.  The patient says that he feels well except for excessive sweating.  He has no history of major medical illness and takes no medications.  Both parents are of average height and have normally proportioned limbs.  The patient is above the 99th percentile for height and at the 90th percentile for weight.  On physical examination, he has long extremities with large hands and feet; the lower jaw is protruding.  Heart sounds are normal.  Sexual development is Tanner stage 4.  Which of the following is the most likely underlying cause of this patient's condition?

A) Aneuploidy of the X chromosome
B) De novo mutation in the fibrillin-1 gene
C) Defective growth hormone receptor
D) Excessive liver production of IGF-1
E) Excessive thyroxine production
F) Increased hypothalamic release of IGF-1
G) Increased pituitary gonadotropin release

Correct Answer:

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