A possible interpretation of the difference in the β coefficients is that posttranslational modifications affect the degradation of neurofilaments.4 For example, phosphorylation on carboxyl terminal domains of NfH and NfM increases their resistance to protease cleavage.3,6 Considering that NfM colocalizes with the dopamine D1 receptor in synapses,6 the prognostic value of the NfM level in PD should be explored. This evidence concerns the gene DRD1 and Parkinson disease.