Loss of Y chromosome and its implications in male amyotrophic lateral sclerosis: insights from the UK Biobank

BACKGROUND: Amyotrophic lateral sclerosis (ALS) shows a male predominance, yet the underlying mechanism remains unclear. Although the loss of Y chromosome (LOY) in peripheral blood - a male-specific genetic alteration - has been implicated in certain neurodegenerative disorders (NDDs), its association with ALS in men remains unexplored and has not been explored. METHODS: We focused on men in the UK Biobank to investigate whether LOY influences the risk and prognosis of ALS. Initially, the LOY level for each male participant was determined using sequencing data. Subsequently, Cox proportional hazards (Cox PH) model analysis was used to assess LOY-associated risk of ALS; thirdly, piecewise linear regression, Kaplan-Meier, and Cox PH analysis assessed LOY's associations with ALS age at onset (AAO) and survival. Fourthly, multiple analytical methods were implemented to explore the relationship between LOY and ALS indicators, including plasma GFAP (glial fibrillary acidic protein) and NfL (neurofilament light chain). Finally, sensitivity analysis was carried out. RESULTS: Our final cohort consisted of 158,953 male participants, with a mean follow-up of 11.7 years. Among them, 297 individuals developed ALS. After adjusted multiple confounding factors, including C9orf72 hexanucleotide repeat expansion (HRE), male participants with LOY exhibited an elevated risk of developing ALS (HR 95% CI: 1.619 1.059-2.475, p = 0.026). LOY carrier may be more likely to be associated with a later AAO and shorter survival; however, this association did not reach statistical significance in multivariate models. Additionally, our findings revealed that LOY was significantly associated with elevated plasma NfL levels (p = 0.004). Moreover, the median Log2 R ratios of Y chromosome (mLRRY value) exhibited a modest inverse correlation with plasma GFAP levels (Pearson's r = - 0.059). Nevertheless, LOY did not exert an influence on the longitudinal trends of NfL and GFAP and was not clearly associated with C9orf72 HRE status. CONCLUSIONS: Our results indicate that LOY makes a potential contribution to the risk of ALS and the elevation of plasma NfL levels. While LOY's impact on ALS AAO and survival requires further validation, these findings identify it as a promising sex‑specific therapeutic target and support its potential for stratifying male ALS patients toward personalized treatments.