Progressive Supranuclear Palsy in India: Insights from a Large Multicenter Clinical Cohort (Project PAIR-PSP)

The Project PAIR-PSP study presents the largest systematically profiled Indian cohort of 1,035 Progressive Supranuclear Palsy patients, revealing a diverse phenotypic distribution with a high frequency of non-Richardson's variants, distinct clinical trajectories across subtypes, and limited pharmacological response to levodopa.

The Gist

Imagine the human brain as a vast, bustling city. In most people, the traffic flows smoothly, and the roads (neural pathways) are well-maintained. But in a rare condition called Progressive Supranuclear Palsy (PSP), it's as if a specific type of "road construction debris" (a protein called tau) starts piling up in the city center. This debris clogs the main intersections, causing traffic jams that lead to falls, confusion, and trouble moving or speaking.

For decades, doctors have been studying this "traffic jam" mostly in cities in Europe and North America. They knew a lot about how it looked there, but they were missing the map for the rest of the world.

The Big Map-Making Project (Project PAIR-PSP)
This paper is like a massive, nationwide survey conducted across India. The researchers, led by Dr. Prashanth Lingappa Kukkle, gathered data from 1,035 patients across 18 different medical centers, from the snowy north to the tropical south. Think of this as sending out 18 teams of surveyors to map every corner of the country to understand how this "traffic jam" behaves in a population of 1.4 billion people.

Here is what their map revealed, broken down simply:

1. The "Traffic Patterns" Vary by Neighborhood

Just as traffic in Mumbai might look different from traffic in rural Kerala, the symptoms of PSP looked different depending on the patient's background and age.

• The Classic "Richardson's" Pattern: About 41% of patients had the "classic" version, where the first major sign is falling over (like a car losing its brakes). This was the most common type.
• The "Parkinsonism" Pattern: About 18% had a version that looked more like Parkinson's disease (stiffness and slowness) but didn't respond well to standard Parkinson's medicine.
• The "Frontal" Pattern: About 7% started with personality changes or thinking problems, like a driver who suddenly forgets the rules of the road or gets angry at traffic lights.
• The "Speech" Pattern: A very small group (1.4%) started with severe speech and language issues, almost like the city's radio station suddenly going silent.

Key Finding: India has a much higher number of these "non-classic" patterns compared to what was seen in Western studies. It's as if the "debris" in India clogs the city in more creative and varied ways.

2. The "Speed of the Jam"

The researchers tracked how fast the "traffic" got worse.

• The Fast Lane: Patients with the "Richardson's" type and the "Speech" type hit the worst milestones (like needing a wheelchair or losing the ability to swallow) very quickly. It's a steep, fast slide.
• The Slow Lane: Patients with the "Parkinsonism" type moved much slower. They could stay on their feet and independent for years longer.
• The "Early Fallers": Some specific groups, like those with "Gait Freezing" (feeling like their feet are glued to the floor), fell down very early in the disease, sometimes within a year of starting.

3. The "Medicine Test"

The team asked: "Does the usual medicine work?"

• They gave a common Parkinson's drug (Levodopa) to nearly 900 patients.
• The Result: It was like trying to clear a massive pile of concrete with a broom. Only about 21% of patients felt a "big" improvement (more than 25%). About 40% felt very little help. This confirms that for most people with PSP, the standard "traffic fix" for Parkinson's doesn't really clear the jam.

4. The "Indian Context"

The study highlighted unique features of this Indian cohort:

• Age: Patients in India tended to get sick slightly younger (average age 62) compared to Western studies (often mid-60s).
• Family Ties: About 10% of patients had a family history of similar movement problems, suggesting that in some families, the "road construction debris" might be passed down like an heirloom.
• Geography: The "Speech" type was almost exclusively found in men, while the "Eye Movement" type had an equal mix of men and women.

The Bottom Line

This paper is a giant "first draft" of a map for understanding PSP in India. It tells us that while the core problem (the tau debris) is the same everywhere, the way it plays out in India is distinct. It shows that the disease is more diverse, starts a bit earlier, and has different "speed limits" for different subtypes than previously thought.

The researchers conclude that this massive dataset is the foundation they need. Just as you can't fix a city's traffic without a good map, you can't find a cure for PSP without understanding how it behaves in diverse populations like India. They are now using this map to look for genetic clues and to plan future studies that might one day lead to better treatments.

Technical Summary

Technical Summary: Progressive Supranuclear Palsy in India: Insights from a Large Multicenter Clinical Cohort (Project PAIR-PSP)

Problem Statement
Progressive Supranuclear Palsy (PSP) is a rare, devastating primary tauopathy with limited global data. Existing large-scale epidemiological and clinico-pathological studies are predominantly derived from Europe and North America, leaving populations from the Global South, particularly India, grossly underrepresented. Given India's vast population, high genetic diversity, and the high frequency of the MAPT H1 haplotype, the lack of systematic data from this region hinders the refinement of diagnostic frameworks, the understanding of phenotype-genotype interactions, and the enrichment of the global narrative regarding PSP and tauopathies. Previous Indian studies have been largely single-center, limiting the ability to capture the full spectrum of clinical heterogeneity and geographic variation within the country.

Methodology
This study, titled Project PAIR-PSP, represents a pan-India multicenter collaborative initiative conducted under the Parkinson's Research Alliance of India (PRAI).

• Study Design: A prospective observational cohort study conducted between April 2021 and July 2025.
• Participants: 1,035 subjects fulfilling the Movement Disorder Society (MDS) clinical diagnostic criteria for PSP were recruited from 18 movement disorder centers across India.
• Data Collection: Standardized demographic, clinical, and treatment-related data were collected via a secure digital platform. Diagnostic certainty (Probable, Possible, Suggestive) and phenotypic sub-classification were recorded based on the predominant presenting clinical syndrome.
• Phenotyping: While adhering to MDS-PSP criteria, the study pragmatically retained rare atypical phenotypes not explicitly encompassed in the current framework (e.g., PSP-Cerebellar) based on expert investigator assessment. Speech and language impairment was identified via routine clinical history and examination.
• Genetic Integration: Peripheral blood samples were collected for genomic analysis in collaboration with MedGenome Labs and the Global Parkinson's Genetic Program (GP2).
• Analysis: The study analyzed demographic profiles, age-at-onset stratification, disease duration, diagnostic certainty, and clinical milestones (falls, cognitive decline, urinary dependence, dysphagia, mobility loss) across various PSP subtypes.

Key Contributions

• Scale: This is the largest systematically profiled PSP cohort from India to date and one of the largest global series on the clinical profile of PSP, significantly adding to the underrepresented population data.
• Pan-Indian Representation: The cohort reflects a diverse geographic distribution (South 35%, North 26%, West 21%, East 18%) and sociocultural strata, offering a more comprehensive view of the disease in a high-diversity population.
• Subtype Characterization: The study provides detailed clinical profiles for nine distinct PSP phenotypes, including rare variants like PSP-Speech/Language (PSP-SL) and PSP-Cerebellar (PSP-C), which are often underreported in Western cohorts.
• Longitudinal Milestones: The paper establishes distinct trajectories for clinical milestones (e.g., time to falls, loss of mobility) across different subtypes, highlighting variations in disease progression and survival.

Results

• Demographics: The cohort consisted of 1,035 patients (Male:Female = 709:326; 68.5% male). The median age was 65 years, with a mean age at symptom onset of 62.2 ± 7.9 years. The mean disease duration at recruitment was 39.3 ± 26.8 months.
• Phenotypic Distribution: PSP-Richardson's Syndrome (PSP-RS) was the most common phenotype (41%), followed by PSP-Parkinsonism (18%) and PSP-Corticobasal Syndrome (11%). Rarer phenotypes included PSP-Postural Instability (7%), PSP-Frontal (7%), PSP-Progressive Gait Freezing (5%), PSP-Ocular Motor (2%), PSP-Speech/Language (1.4%), and PSP-Cerebellar (1.2%).
• Age and Onset: Younger-onset patients (40–49 years) showed longer disease durations at recruitment and higher rates of parental consanguinity. Diagnostic certainty ("Probable PSP") decreased with later age at onset, while "Possible PSP" increased.
• Progression Patterns:
  • PSP-RS: Exhibited the most aggressive course, with falls occurring early (mean 21 months) and rapid progression to mobility dependence.
  • PSP-Parkinsonism: Showed a slower progression, with delayed falls (31 months) and a relative survival advantage, comprising over half of the >10-year survivors.
  • PSP-SL: Despite being rare, this variant showed an extremely aggressive non-motor course with rapid speech decline and early cognitive disability.
  • PSP-PGF: Characterized by the earliest onset of falls (13.7 months) and early axial disability.
• Treatment Response: Levodopa was prescribed to 893 patients (86%), but sustained benefit was limited; only 21% reported >25% subjective improvement. Amantadine was used in 34% of patients, with improvement noted in roughly half of those users.
• Comparative Data: Compared to other South Asian and global cohorts, the Indian cohort showed a higher frequency of non-RS variants (59% vs. ~33% in UK South Asian cohorts) and a younger mean age at onset.

Significance and Claims
The authors claim that this study establishes a critical foundation for longitudinal and genetic studies in diverse populations. By providing the most extensive systematic clinical profiling of PSP from India, the study:

1. Bridges a Data Gap: It addresses the historical underrepresentation of South Asian populations in global PSP research, offering insights into how genetic diversity and environmental contexts influence the disease.
2. Refines Phenotypic Understanding: The data highlights shared features with global cohorts (e.g., male predominance, core oculomotor signs) while revealing distinctive regional patterns, such as a higher proportion of non-RS variants and specific regional clustering of certain subtypes (e.g., PSP-PI and PSP-PGF in South India).
3. Informs Future Research: The cohort serves as a benchmark for future work, including genotype-phenotype correlation studies (currently ongoing with GP2) and the development of disease-modifying therapies. The authors emphasize that insights from such large, diverse populations are indispensable for informing equitable global clinical trials.

The paper modestly acknowledges limitations, including the potential for phenotype evolution over time, referral center bias toward more severe cases, and the lack of a uniform formal language battery across centers. However, it positions the PAIR-PSP cohort as a robust resource for advancing the understanding of PSP heterogeneity and progression in a genetically diverse setting.