Neurofilament light chain as a blood biomarker to differentiate psychiatric disorders from behavioural variant frontotemporal dementia

The overlapping symptoms of behavioural variant frontotemporal dementia (bvFTD) and primary psychiatric disorders (such as depressive disorder, schizophrenia spectrum, and bipolar disorder) present a challenge for the differential diagnosis of bvFTD in middle and older-aged people. Neurofilaments are cytoskeletal proteins in the neurons, and several studies have reported elevated levels of neurofilament light chain (NfL) in cerebrospinal fluid of neurodegenerative as well as psychiatric disorders. The study aims to determine the utility of serum NfL levels as a biomarker to differentiate between bvFTD and psychiatric disorder. In our study, we investigated the levels of NfL in the serum of schizophrenia (n = 11), depression (n = 28), bipolar (n = 11), bvFTD (n = 20) patients and controls (n = 27) by single molecule array (Simoa) technology. The schizophrenia, depression and bipolar patients did not show significant changes in serum NfL levels in comparison to the control group (p > 0.99). The serum NfL levels were significantly elevated in bvFTD patients in comparison to the control cohort (p < 0.0001), depression (p < 0.0001), schizophrenia (p < 0.0002) and bipolar patients (p < 0.0083). We propose serum NfL as a biomarker to differentiate bvFTD from psychiatric disorders and to rule out neurodegeneration in the course of psychiatric disorders.