10-13 Molecular genetic studies described an involvement of a polymorphism of the dopamine transporter (DAT) 1 gene in ADHD (eg, a higher rate of homozygosity of the 10-repeat allele in the 3 ‘untranslated region of exon 15 of the DAT gene on chromosome 5p15.3).14-19 With regard to the suspected striatal impairment in ADHD and the known effect of methylphenidate on the DAT mainly localized in this section of the brain, since the end of the 1990s DAT has been investigated in patients with ADHD. This is carried out by using radioactive marked ligands which are known to bind effectively with the DAT system. A group

of investigators from Rapamycin ic50 Boston used altropane marked with iodine-12320; Inhibitors,research,lifescience,medical our group from Munich and Philadelphia used the cocaine derivative TRODAT-1 marked with technetium 99m.21 Both studies showed a clearly higher availability of DAT in the Inhibitors,research,lifescience,medical striatum of adult patients with ADHD compared with the normal healthy controls.20-23 While DAT availability was found to be raised to 17% in the investigations using TRODAT-1 compared with the control collective (Figure 2), the group using altropane demonstrated a rise of 70% in 6 patients; this percentage was reduced to around 30% in a larger group of 19 patients on continuation of the altropane study (Spencer T, personal communication). Meanwhile, a rise in DAT availability was also detected in

the basal ganglia Inhibitors,research,lifescience,medical of children with ADHD by means of an [123I] N-(3-iodopropen-2-yl)-2-carbo-methoxy-3β-(4-chlorphenyl) tropane (IPT)-SPECT investigation,24 following initial results with N-δ-fluoropropyl-2 β-carboxymethoxy-3 β-4-iodophenyl tropane

(FP-CIT).25 Interestingly, a rise in the DAT Inhibitors,research,lifescience,medical could not, be detected in a SPECT investigation with β-CIT26; this could be due to the extremely slow kinetics of β-CIT (measurement 1 day after application) or another specificity of this Inhibitors,research,lifescience,medical radiotracer, which also binds with serotonin transporters and possibly holds other substructures of DAT compared with altropane, FP-CIT, IPT, or TRODAT-1. Our own initial results revealed that the DAT was raised not. only in the hyperactive-impulsive and combined type, but also in the inattentive type Dipeptidyl peptidase of ADHD (Figure 3). It, may be deduced from a neurochemical view that with an increase in DAT, which transports dopamine back from the synaptic cleft, less dopamine is available in the synaptic cleft of dopamine-dependent neurons. The results obtained by our group showed not, only the impairment of DAT but also reported for the first, time in vivo and intraindividually in patients with ADHD, that impaired metabolism can be improved with methylphenidate: on administration of 5 mg 3 times daily it was seen that there was a clear reduction in DAT availability in all patients after a period of 4 weeks (Figure 2).22,23 With this very low dose, most of these patients demonstrated a lower concentration of DAT than did the control group.