Manganese concentrations in biological matrices and amyotrophic lateral sclerosis (ALS): a systematic review and meta-analysis.

BACKGROUND

Manganese (Mn) is an essential but neurotoxic trace element implicated in neurodegenerative disorders. Its association with amyotrophic lateral sclerosis (ALS) remains uncertain. We conducted a systematic review and meta-analysis to evaluate whether Mn concentrations differ between ALS patients and healthy controls.

METHODS

We systematically searched PubMed, EMBASE, Web of Science, and Scopus for observational studies comparing Mn concentrations between ALS patients and healthy controls. Standardized mean differences (SMDs) with 95% confidence intervals (CIs) were pooled using a random-effects model. Heterogeneity was assessed with the I² statistic, and publication bias was evaluated by Egger's test.

RESULTS

Twelve studies (446 ALS cases, 652 controls) measuring Mn in blood, serum, cerebrospinal fluid (CSF), hair, urine, toenail, plasma, or tissue were included. The pooled SMD was 0.05 (95% CI: - 0.20 to 0.30; p = 0.68; I² = 71.7%), indicating no significant difference in Mn concentrations. Subgroup analyses by biological matrix and analytical method showed no consistent pattern; meta-regression identified analytical method as a significant source of heterogeneity.

CONCLUSION

No publication bias was detected (Egger's p = 0.53). Peripheral Mn concentrations do not differ significantly between ALS patients and controls. Future research should employ longitudinal and CNS-targeted approaches, incorporating occupational exposure assessment and standardized analytical protocols.