The situation is further complicated by limitations of current testing methods – this is especially the case when relying on positive serum IgG or IgM antibody tests as opposed to actual detection of the virus, as has been the case in some studies of anosmia, for example.135 There are many more uncertainties with the sensitivity and specificity of antibody tests, increasing the chance of error when associating neurological manifestations with COVID-19. Here, CD40LG is linked to Kallmann syndrome.