Therefore, we performed a serological evaluation of IgG antibodies against HERV-K Env epitope (HERV-K Env19–37) in comparison to an important β-cellular autoimmunity biomarker, ZnT8, from plasma samples of Sardinian children at the onset of T1DM, different T1DM groups (1–5 and 6–12 years since diagnosis), and healthy controls (HCs), by an indirect enzyme-linked immunosorbent assay (ELISA). The gene discussed is ERVW-1; the disease is type 1 diabetes mellitus.