A genetic disorder characterized by a CGG trinucleotide repeat expansion in the 5' untranslated region of the FMR1 gene, leading to anticipation and intellectual disability, is most consistent with which diagnosis?

The correct answer to the question "A genetic disorder characterized by a CGG trinucleotide repeat expansion in the 5' untranslated region of the FMR1 gene, leading to anticipation and intellectual disability, is most consistent with which diagnosis?" is Option B: Fragile X Syndrome.

The other options — A) Huntington's Disease, C) Myotonic Dystrophy, D) Spinocerebellar Ataxia Type 1 — are incorrect for this USMLE Exam Prep question. As explained above: Fragile X Syndrome is caused by a CGG trinucleotide repeat expansion in the FMR1 gene's 5' UTR, leading to gene silencing and intellectual disability. It is a classic example of anticipation.