A 2-year-old boy is brought to the family doctor by his concerned mother. She is worried he is not growing normally despite always being hungry and eating much more than his older sister did. His mother also mentions that he becomes very upset with changes to routine and struggles to interact with others. He had trouble sitting upright earlier in infancy and only recently learned to walk. Despite being heavier now, his mother mentions he had trouble feeding and growing in the first year of life. On physical examination, the boy is clinically obese but short for his age and cries throughout the examination. A narrowed nasal bridge and a down-turned mouth are noted, as well as hypotonia. A genetic cause is suspected given the presentation.
Which of the following is the most likely underlying pathophysiology present in this child?
- A) Balanced translocation between chromosomes 8 and 14 (t8; 14)
- B) De novo mutation in paternal chromosome 15
- C) Hypermethylation of paternal UBE3A gene
- D) Terminal deletion on chromosome 5
- E) Trinucleotide CGG repeat expansion in FMR1 gene