SLC19A3 and biotin-responsive basal ganglia disease: In two adult siblings with BBGD, two heterozygous mutations in SLC19A3 (c.74dupT/p.Ser26LeufsX19 and c.980-14 A>G) led to a premature termination codon (PTC), and a loss of function mutation of SLC19A3. One patient responded to biotin, but the other did not improve with biotin administration until thiamine was concurrently supplemented.[18] However, since hTHTR2 does not transport biotin, both the pathophysiology of BBGD, and the response to therapy with biotin imply that a more complex mechanism than simple thiamine deficiency causes these lesions [19].