Furthermore, not only the presence but also the levels of mcm5s2U-modified tRNAs seem to be a factor to consider, as not only knockouts must be studied as models, for example, in the case of IKAP (Elp1) to recapitulate Familial dysautonomia in mice, it was required to develop hypomorphic allele and not a complete knock-out [40], indicating that in some cases the relevant and realistic model, in terms of a pathological condition, might not be the lack of a particular modification, but rather diminished levels. This evidence concerns the gene ELP1 and dysautonomia.