NfL is a sensitive marker of neuroaxonal degeneration which is elevated in CSF and blood in the symptomatic stage of genetic FTD40 and in various other neurological disorders.21 Although a trend was found for symptomatic carriers alone after exclusion of ALS patients (who are known to have very high NfL levels),21 the lack of a stronger correlation probably reflects that NPTX2 and NfL are markers of different pathological processes which do not occur simultaneously. The gene discussed is NPTX2; the disease is nervous system disorder.