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HD Anticipation – Juvenile Variant — SCE Neurology MCQ

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HardNeurogeneticsHD Anticipation – Juvenile VariantSCE Neurology

A 10-year-old boy (discussed at transition MDT) with Huntington disease symptoms at age 8 has the juvenile (Westphal) variant. His father was diagnosed with HD at age 40. The boy's CAG repeat length is 72 (his father's is 44). What genetic phenomenon explains the earlier onset and longer repeat in the child?

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Correct answer: E — Anticipation — the CAG repeat length tends to expand during intergenerational transmission, particularly through the paternal line, causing earlier onset and more severe disease in successive generations

Anticipation is the tendency for trinucleotide repeat disorders to increase in repeat length with each generation, causing earlier onset and more severe disease. In HD, this is particularly marked with paternal transmission (spermatogenesis involves more cell divisions, allowing more repeat expansion). The juvenile (Westphal) variant of HD (onset <20 years) typically has very long repeats (>55) and presents with rigidity, dystonia, seizures, and rapid cognitive decline rather than the chorea seen in adult-onset HD. A: The expansion is systematic, not random. C: Incomplete penetrance involves reduced expression. D: Imprinting involves parent-of-origin gene silencing. E: HD is autosomal dominant.

Reference: EAN HD Guidelines; Walker FO HD Review