Abstract: The invention concerns a novel nucleic sequence and deduced protein sequence family with whole or partial human endogenous retroviral motifs. The invention also concerns the detection and/or the use of said nucleic sequences and said corresponding protein sequences or fragments of said sequences, for diagnostic, prophylactic and therapeutic uses, in particular for neuropathological conditions with autoimmune constituent such as multiple sclerosis. Said purified nucleic acid sequences comprise all or part of a sequence coding for a human endogenous retroviral sequence having at least eny-type retroviral motifs, corresponding to the sequence SEQ ID NO:1 or to a sequence having a homology level with said sequence SEQ ID NO:1 not less than 80% of more than 190 nucleotides or not less than 70% on more than 600 nucleotides for env-type domains. The invention further concerns the use of the flanking or adjacent sequence of said sequences and controlled by the latter, as diagnostic reagents.