Author response: Blood NfL: A biomarker for disease severity and progression in Parkinson disease.

Abstract

We thank Rumund et al. for interest in and comment on our article.1 Rumund et al. described the blood NfL levels' increase in patients with multiple system atrophy (MSA) in their study,2 which is consistent with our findings. By contrast, they found no significant difference between patients with Parkinson disease (PD) and controls. One of the reasons may come from the number and severity of recruited patients with PD. Our findings revealed that the blood NfL levels were comparable between patients with Hoehn-Yahr stage I–II and controls. However, it was significantly increased in patients with Hoehn-Yahr stage IV–V.2 A recent study assaying the longitudinal dynamics of blood NfL levels found that NfL levels were similar between subjects at the prodromal phase and controls; however, subjects—who later converted to motor PD—had a significant increase of age-dependent acceleration of NfL levels.3 Furthermore, another recent study revealed that the blood NfL levels were increased in de novo patients with PD and were associated with poor cognitive performance.4 This emerging evidence suggests that the blood NfL level is a promising marker for PD progression, albeit the diagnostic cutoff values remain to be determined by well-designed large-scale longitudinal studies.