In the 1990s, Carlson et al. showed that de novo RET M918T mutation always occurred on the paternally-derived chromosome, suggesting a differential susceptibility of RET to mutation in parental-derived DNA, but showed at the same time that RET does not map to a known imprinted locus and revealed that both parental RET alleles are expressed in MEN2-related tumours [153]. This evidence concerns the gene RET and neoplasm.