It is becoming increasingly clear that NF-L presence in biofluids alone however, is neither specific or selective for AD or for any other progressive age-related neurological disorder [12,29,65,92].The highest value of measuring the abundance of NF-L as a biomarker in CSF may be to differentiate between complex neurological disorders with close and often overlapping clinical presentation, such as assisting the differentiation between FTD (the second most frequent cause of dementia, after AD in patients under the age of 65) from AD, and PD from atypical Parkinsonian syndromes [47,91,93]. The gene discussed is NEFL; the disease is Parkinson disease.