SLC29A3 and H syndrome: However, hENT3-variant3-81fs displayed significant higher levels of transporter activity compared to hENT3-variant1-81fs or hENT3-variant3-WT, or even hENT3-variant1-314fs or hENT3-variant1-349fs, two mutants leading to PHID and H syndrome respectively [16], [19] (Figure 4D).