A 3-Year-Old Boy Is Brought to the Office for Follow-Up

question 15

Multiple Choice

A 3-year-old boy is brought to the office for follow-up on intellectual disability and speech delay.  Review of his developmental screening questionnaire shows that the boy does not imitate his parents' activities, have a social smile, or show interest in other children.  The patient has 8-10 words in his vocabulary and does not combine them into 2-word phrases.  There is also concern that his verbal comprehension is poor, and a subsequent audiological evaluation was normal.  The boy is up to date on all vaccinations and has no other significant medical history.  Laboratory testing shows 226 CGG trinucleotide repeats in a gene located on the X chromosome.  Which of the following is the most likely cause of this patient's clinical condition?

• A)Exon deletion
• B)Gene methylation
• C)Impaired intron splicing
• D)Imprinting
• E)Mismatch repair defect

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