Furthermore human DAT mutants of atypical juvenile DTDS cases demonstrate some residual and even up to normal levels of expression of mature transporter protein at the cell surface (Henriksen et al., 2012), whereas surface expression of mature DAT in classical infantile-onset DTDS is severely reduced or absent (Kurian et al., 2009, 2011a). This evidence concerns the gene SLC6A3 and SLC6A3-related dopamine transporter deficiency syndrome.