In addition to the CNS, NfL is also found in the peripheral nervous system (PNS) and previous studies have found elevated P-NfL in diseases affecting the PNS.50,51 None of the individuals included in our study had a symptomatic confounding neurological disease affecting the CNS or the PNS, suggesting that P-NfL levels reflect ongoing neuronal injury related to HIV or homocysteine metabolism. This evidence concerns the gene NEFL and nervous system disorder.