The blood expression of HNMT was also found to be upregulated is TD patients aged 13–16 (FC = 1.70), while that of SLC22A3 was downregulated in TD patients aged 10–13 (FC = −1.10) and positively correlated with TD severity [66,67], further suggesting a dysregulation of histamine metabolism in TD. This evidence concerns the gene HNMT and thanatophoric dysplasia.