Urinary P75: a promising biomarker for amyotrophic lateral sclerosis

Background: Amyotrophic lateral sclerosis (ALS) is a progressive and fatal disease. The urinary neurotrophin receptor p75 extracellular domain (p75 ECD) has previously been reported as a potential disease biomarker for diagnosis, severity assessment and monitoring therapeutic response. 

Methods: This study measured urinary p75 ECD using an enzyme-linked immunoassay and normalised the results against urinary creatinine. Participants were recruited via A Multicentre Biomarker Resource Strategy in ALS (AMBroSIA) programme. Study participants included 97 ALS patients, 24 of whom were studied longitudinally, and 27 healthy controls. The study focused on urinary p75 ECD and its potential association with different subtypes of ALS, change over time, disease progression, severity of symptoms and survival from symptom onset. 

Results: Confirming previous findings, urinary p75 ECD levels were significantly higher in patients with ALS (median 6.78 ng/mg, 95% CI (5.12 to 9.23)) compared with controls (4.57 ng/mg, 95% CI (3.35 to 5.89)) at first study visit. There was a significant negative correlation between absolute change in the Revised ALS Functional Rating Scale score and p75 ECD levels (Spearman's rho=-0.371, p≤0.0004, 95% CI (-0.543 to -0.169)), indicating that an increase in the severity of motor neuron injury correlated with an increase in p75 ECD levels. There was a significant increase in p75 ECD between first and second samples in the same participants, indicating an increase in the level of this biomarker longitudinally during the disease course (moderate effect size of -0.3). 

Conclusions: Urinary p75 ECD is a promising candidate as a biomarker, which increases with disease progression and has the potential to serve as a pharmacodynamic biomarker.