α-Synuclein Aggregates in Parkinson’s Disease

Group 30: SAA Analysis from PPMI Projects 155 & 237

Malaika Khiljee
Karolina Nordkamp
Isabella Christoffersen
Andreas Nielsen

2025-12-02

Introduction

  • Presynaptic neuronal protein α-Synuclein

  • Aggregation between nerve cells -> inhibition of transmission

  • 2 Projects using SAA (α-synuclein seed amplification assays)

  • 24h versus 150h


General focus:

Does one of the methods perform better than the other, and which is one more efficient?

Materials and Methods

Materials:

  • PPMI (Parkinson’s Progression Markers Initiative) database

  • 3 replicates of SAA (cerebrospinal fluid)

  • Monitors the aggregation by measuring fluorescence intensity over time

  • Sigmoidal curve: fmax, auc, ttt

  • Set of critera for positive/negative/inconclusive


Methods:

  • Tidyverse

  • fmax values, means

  • Patterns, distinction, t-test, standard deviation

Tidying and augmenting

  • Tidy data makes it much easier to handle. Requirements:

    • Each column is one variable (Not the case initially)

    • Each row is one observation

    • Each cell is one value

Augmenting

  • Days from baseline: Calculated from rundates

  • Mean of fmax for each visit

  • Our own SAA_result

Descriptive

  • Two projects: 155 (150h) and 237 (24h)


  • 1300 individuals, almost 1900 observations




  • Frequency of instrument used

SAA quality check

  • SAA result and SAA custom quality check

  • A non-mentioned criteria?

  • Low fmax (200–600 RFU), huge, moderate

  • Hard to know for sure

Result Project 155
Positive All replicates Fmax ≥ 5,000 RFU
Negative 0 or 1 replicate Fmax ≥ 5,000 RFU
Inconclusive 2 replicates Fmax ≥ 5,000 RFU

SAA results

Alternative diagnostic variables

  • Fmax_mean


  • Statistically significant difference in both 24h and 150h SAA


  • AUC, SLOPE, T50 and TTT


Inconsistencies in the two projects (replicates)

  • Can standard deviations in replicates say something about whether one project is better than the other?

Project Mean SD Median SD IQR
155 24,066 22,198 26,131
237 10,386 5,662 6,470
  • Can the instruments explain some of these differences?

Mean fmax over time

Question: Does the signal become stronger further into disease progression?

  • Only for project 237 above

    • Not necessarily comparable fmax mean values

    • Project 155 only had close to baseline measurements

  • No connection

  • Note: Days from baseline is a not actually a measure of disease progression…

  • Patient variation, if any connection at all

  • We also looked at more patients

Last notes/conclusions

24-hour assay (237) vs 150-hour assay (155):

Does one of the methods perform better than the other, and which is one more efficient?

  • Project 237: Fast, clear separation, consistent

  • Healthy controls for better assessment