In a previous study we found that nine of 47 siblings to multiple sclerosis (MS) patients with a normal neurological examination carry an intrathecal oligoclonal immunopathy with limited specificity, a condition we termed MS immunopathic trait. The purpose of this study is to further characterize the MS immunopathic trait phenotype. We found that the neurofilament light protein (NFL) and glial fibrillary acidic protein (GFAp) concentrations were increased in the group of patients with clinically definite MS (n = 47) in latent or slowly progressive phases. There was no increase in GFAp and NFL in cerebrospinal fluid in the healthy siblings of MS patients (n = 47), nor in the subgroup of these siblings with MS immunopathic trait (n = 9) compared with a group of healthy control subjects (n = 50). Thus, there was no indication of presymptomatic CNS parenchymal involvement in MS immunopathic trait.