LETTERTOTHEEDITOR Parkinson’s disease in GTP cyclohydrolase 1 mutation carriers

We read with great interest the recent article by Mencacci et al. (2014) about the increased risk for Parkinson’s dis-ease in carriers of GCH1 mutations. GCH1 mutations are the most common cause of DOPA-responsive dystonia (DRD), a disorder characterized typically by lower limb dystonia with onset in childhood, an excellent, sustained response to levodopa, absence of levodopa-induced dyskin-esias, and absence of dopaminergic neurodegeneration as evidenced by normal dopamine transporter (DAT) imaging. Inheritance of GCH1-linked DRD is autosomal dominant and penetrance is incomplete (Charlesworth et al., 2013). Mencacci et al. (2014) demonstrated that some GCH1 mu-tation carriers who did not manifest DRD during child-hood, developed adult-onset parkinsonism with imaging evidence of dopaminergic neurodegeneration. Thus, th