Pre-registration: does the striatal medium-spiny-neuron marker score in human Huntington's disease caudate depend on expanded CAG repeat length after age and sex? (GEO GSE3790)

Frozen pre-registration (3 Nov 2026) of an analysis of public microarray data (GEO GSE3790, platform GPL96; Hodges et al. 2006): in 35 adult HD caudate donors (HD grade 1-4 with genotype), is the mean z-scored expression of nine MSN marker genes (DRD1, DRD2, ADORA2A, PENK, TAC1, GPR88, PDE10A, RGS9, GPR6) lower with longer expanded CAG repeats, adjusting for age and sex (standardised coefficient at most -0.3 with a one-sided 95 percent donor-bootstrap upper bound below zero)? Written before any expression value was read. Design-only power is stated (47 percent at a standardised slope of -0.3, 66 percent at -0.4, 83 percent at -0.5). Controls: positive (HD versus control caudate), frontal-cortex negative control, 1,000 matched random gene sets, CAG shuffle null, planted effect, probe-rule and seed stability. Contains the analysis code and synthetic tests. Computational analysis of public data, not an experimental validation. Outcome wording: Supported (not falsified) / Not demonstrated / Inconclusive.