The change in circulating GDF-15 was 0.028 SD (95% CI, −0.001 to 0.058; p = 0.062) per one-unit increase in log-OR of PD, whereas it was −0.002 SD (95% CI, −0.078 to 0.075; p = 0.966) for ALS. This evidence concerns the gene GDF15 and amyotrophic lateral sclerosis.