Phenotypic spectrum of progressive supranuclear palsy: clinical study and APOE effect

Objectives:Progressive supranuclear palsy (PSP)is a rare neurodegenerative disorder encompassing several phenotypes with various motor and cognitive deficits.We aimed to study motor and cognitive characteristics across PSP phenotypes,and assess the influence of the Apolipoprotein E (APOE)gene variants on PSP phenotypic expression. Materials and Methods:In 20-year-cross-sectional study, we retrospectively reviewed the charts of all patients classified as PSP and re-categorized them into phenotypes using the MDS-2017 criteria. Phenotypes were divided into three subgroups based on the clinical presentation during the first 3 years after symptoms' onset, which defines the early disease stage:Richardson's syndrome (PSP-RS), PSP-cortical (PSP-F+PSP-SL+PSP-CBS) and PSP-subcortical(PSP-P+PSP-PGF+PSP-PI+PSP-OM+PSP-C+PSP-PLS).Data on clinical and neuropsychological assessments were collected.Genotyping of APOE was performed using the RFLP-PCR and verified by Sanger sequencing. Results:We included 112 PSP patients comprising 10 phenotypes classified into 48PSP-RS, 34PSP-cortical(17.6%PSP-CBS,9.4%PSP-F,8.2%PSP-SL)and 30 PSP-subcortical(11.6%PSP-P,8%PSP-PI, 2.6%PSP-OM,1.8%PSP-PGF,1.8%PSP-C,0.9%PSP-PLS) subgroups. PSP-RS cases had older age of onset(p=0.009)and more akinetic-rigid and levodopa resistant parkinsonism(p=0.006),while PSP-cortical cases had more tremor and asymmetric and/or levodopa responsive parkinsonism(p=0.025).Cognitive domains were significantly less altered among PSP-subcortical subgroup.Overall,PSP-APOEε4 carriers developed parkinsonism earlier (p=0.019),had earlier oculomotor dysfunction(p=0.052) and more altered cognitive profile.It was also associated with younger age of parkinsonism onset in PSP-RS phenotype(p=0.026). Conclusion:This study demonstrated the wide phenotypic spectrum of PSP among Tunisians.Later disease onset and akinetic-rigid and levodopa resistant parkinsonism were the hallmarks of PSP-RS phenotype,while milder cognitive impairment was characteristic of PSP-subcortical subgroup.APOEε4 allele was associated to earlier parkinsonism and oculomotor dysfunction and seemed to play a role in defining a more altered cognitive profile in PSP patients.