Phenotypic Spectrum of Progressive Supranuclear Palsy: Clinical Study and Apolipoprotein E Effect

Abstract

Objective: 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 to assess the influence of apolipoprotein E (APOE) gene variants on PSP phenotypic expression.

Methods: In this 20-year cross-sectional study, we retrospectively reviewed the charts of all patients classified as PSP patients and recategorized them according to phenotype using the Movement Disorder Society criteria (2017). Phenotypes were divided into three subgroups, Richardson's syndrome (PSP-RS), PSP-cortical (PSP with predominant frontal presentation [PSP-F] + PSP with predominant speech/language disorder [PSP-SL] + PSP with predominant corticobasal syndrome [PSP-CBS]) and PSP-subcortical (PSP with predominant parkinsonism [PSP-P] + PSP with progressive gait freezing [PSP-PGF] + PSP with predominant postural instability [PSP-PI] + PSP with predominant ocular motor dysfunction [PSP-OM] + PSP with cerebellar ataxia [PSP-C] + PSP with primary lateral sclerosis [PSP-PLS]), based on clinical presentation during the first 3 years after symptom onset, which defines the early disease stage. Clinical and neuropsychological assessment data were collected. Genotyping of APOE was performed using restriction fragment length polymorphism polymerase chain reaction and verified by Sanger sequencing.

Results: We included 112 PSP patients comprising 10 phenotypes classified into 48 PSP-RS, 34 PSP-cortical (PSP-CBS, 17.6%; PSP-F, 9.4%; PSP-SL, 8.2%) and 30 PSP-subcortical (PSP-P, 11.6%; PSP-PI, 8%; PSP-OM, 2.7%; PSP-PGF, 1.8%; PSP-C, 1.8%; PSP-PLS, 0.9%) subgroups. PSP-RS patients were older at disease onset (p = 0.009) and had more akinetic-rigid and levodopa-resistant parkinsonism (p = 0.006), while PSP-cortical patients had more tremors and asymmetric and/or levodopa-responsive parkinsonism (p = 0.025). Cognitive domains were significantly less altered in the PSP-subcortical subgroup. Overall, PSP-APOEε4 carriers developed parkinsonism earlier (p = 0.038), had earlier oculomotor dysfunction (p = 0.052) and had more altered cognitive profiles. The APOEε4 allele was also associated with a younger age of parkinsonism onset in the PSP-RS phenotype group (p = 0.026).

Conclusion: This study demonstrated the wide phenotypic spectrum of PSP among Tunisians. Disease onset and akinetic-rigid and levodopa-resistant parkinsonism were the hallmarks of the PSP-RS phenotype, while milder cognitive impairment was characteristic of the PSP-subcortical subgroup. The APOEε4 allele was associated with earlier parkinsonism and oculomotor dysfunction and seemed to play a role in defining a more altered cognitive profile in PSP patients.

Keywords: Cognition; Cortical; Parkinsonism; Phenotypes; Progressive supranuclear palsy; Subcortical; Tauopathy.

Figure 1.

Neuropsychological and clinical profiles of PSP according to subtype (A, B) and APOE carrier status (C). Radar charts comparing the percentages of PSP-RS, PSP-cortical, and PSP-subcortical patients with neuropsychological findings (A) and Movement Disorder Society PSP diagnostic criteria clinical features (B) and APOEε4 carrier vs. noncarrier Movement Disorder Society PSP diagnostic criteria clinical features (C). PSP-RS, PSP-Richardson’s syndrome; PSP, progressive supranuclear palsy.

Figure 2.

Clinical profile of PSP patients with typical and atypical phenotypes. Radar charts comparing the percentages of PSP-RS (typical phenotype) and PSP atypical phenotype patients according to the clinical features of the Movement Disorder Society PSP diagnostic criteria. PSP-RS, PSP-Richardson’s syndrome; PSP, progressive supranuclear palsy.

Figure 3.

Correlation between clinical variables among PSP subgroups. A: Total cohort. B: PSP-RS. C: PSP-cortical. D: PSP-subcortical. PSP, progressive supranuclear palsy; PSP-RS, progressive supranuclear palsy-Richardson’s syndrome; PSP-cortical, progressive supranuclear palsy-cortical; PSP-subcortical, progressive supranuclear palsy-subcortical.