Preclinical Basal Ganglia Neurodegeneration in Female X Linked Dystonia Parkinsonism Carriers

Background and Objectives: X-linked dystonia-parkinsonism (XDP) is a severe neurodegenerative movement disorder caused by a retrotransposon insertion with a polymorphic hexanucleotide repeat expansion in the TAF1 gene. While the disease predominantly affects males, female carriers may exhibit a variable phenotypic expression. Neurobiological alterations in asymptomatic female mutation carriers (fMC) remain largely unexplored. We aimed to investigate whether fMC exhibit neurodegenerative changes despite the absence of overt clinical manifestations and to assess their clinical, genetic, and longitudinal correlates using multimodal MRI. Methods: In this cross-sectional and longitudinal multimodal study, 103 female relatives of XDP patients underwent clinical, genetic, and MRI assessments. Forty-two were identified as fMC and 61 as healthy controls (HC). Structural T1-weighted MRI was analyzed using voxel-based morphometry and subcortical volumetry, while susceptibility-weighted imaging assessed iron deposition. Clinical evaluation included standardized motor and cognitive testing. Longitudinal follow-up MRI was available for a subset of participants (20 fMC, 13 HC). Results: fMC exhibited significant striatal atrophy compared to HC, with volume reductions in the caudate (-19.4%), putamen (-18.6%), and pallidum (-28.6%) (all p<0.001), despite the absence of overt movement disorders or cognitive deficits, accompanied by relative cerebellar hypertrophy. In fMC striatal volumes decreased with increasing age (putamen: rho=-0.382, p=0.012; caudate: rho=-0.631, p<0.001) and virtual time from genetically determined estimated age at onset (putamen: rho=-0.406, p=0.008; caudate: rho=-0.660, p<0.001). Susceptibility-weighted imaging revealed increased iron deposition in the caudate in fMC, which increased with greater local atrophy (rho=0.718, p<0.001). No significant longitudinal progression was detected over follow-up intervals of up to 25.5 months. Discussion: Asymptomatic female carriers of the XDP-associated TAF1 variant exhibit significant striatal neurodegeneration and iron accumulation, indicating a dominant-negative effect despite X-linked inheritance. Future longitudinal studies should focus on non-motor features and integrate genetic, imaging, and clinical markers to improve risk stratification and identify the subset of female carriers most likely to benefit from future disease-modifying therapies.