Neurofilament Light Chain: A Possible Biomarker to Predict Development of HTLV-1-Associated Myelopathy/Tropical Spastic Paraparesis

Neurofilaments are the main components of the axonal cytoskeleton. Neuroaxonal damage which occurs in different chronic neurological disorders results in the release of Neurofilaments into the cerebrospinal fluid (CSF) and later on into the serum. Thus they are beingintroduced as potential biomarkers for the diagnosis and also the monitoring process of many acute and chronic neurologic diseases. Human T-Lymphotropic virus type 1 (HTLV-1) infection can lead to a progressive neurologic disease called HTLV-1-associated myelopathy/tropicalspastic paraparesis (HAM/TSP). Patients suffer from myelopathic symptoms such as spastic paraparesis, lower limb sensory disturbance and bladder dysfunction. Diagnosis of HAM/TSP is mainly based on clinical finding and on the identification of anti-HTLV antibodies in serumand CSF. But it is sometimes difficult to differentiate between HAM/TSP and myelopathies of unknown origin. The use of potential biomarkers to differentiate these will therefore be quite beneficial. HTLV-1 bZIP factor (HBZ) which is a nuclear protein found in chronically infectedcells with HTLV-1 is shown to be exclusively localized in the cytoplasm of peripheral blood mononuclear cells (PBMC) from patients suffering of HAM/TSP and thus is introduced as possible biomarker for HAM/TSP; but it is further needed to be studied. It has been shown thatin HAM/TSP, only the motor and sensitive tracts of the spinal cord are damaged and the neurons are left intact; thus the degenerative process is limited to axons. This finding supports the possibility of Neurofilaments to be used as biomarkers in HAM/TSP. Also, another studyhas shown that levels of Neurofilament light chain (NFL) was significantly increased in Human Immunodeficiency virus (HIV) associated dementia. Since HTLV-1 and HIV are both retroviruses and have common pathological pathways; the utility of NFLs as biomarkers for thediagnosis of HAM/TSP should be considered in future studies.