The noradrenergic system plays a known role in attentional systems and suspected causal role in attention deficit/hyperactivity disorder(ADHD).Methylphenidate also has been suspected as a inhibitor of norepinephrine transporter(SLC6A2). The investigators hypothesis is that norepinephrine transporter polymorphism is associated with responses and adverse effects of OROS-methylphenidate in treatment of ADHD.