It is also noted that more sensitive means of measuring blood NfL are available, such as single molecule assays.22 Although such assays might improve the lower limit of detection, we note that NfL levels in the majority of non-ALS patients in this study were well within the detection range of our platform, and increased assay sensitivity would not be expected to make any difference to the limitations of blood NfL in this setting. The gene discussed is NEFL; the disease is amyotrophic lateral sclerosis.