GCH1 mutations have previously been associated with a dopa-responsive dystonia-Parkinsonism syndrome. However, mutations of this gene have not yet been associated with a concurrent cerebellar syndrome.

We report the case of a 49 year old gentleman who presented with three years of progressive dystonic posturing of the left foot while walking, stiffness of the left side of the body, and oscillopsia. The patient initially noted progressive oscillopsia with reading and poor speech articulation. One year later, he began to notice inversion of the left foot while walking and increasing stiffness of the left arm and leg. Extensive workup, including MRI brain/spine, lumbar puncture (including CSF and serum paraneoplastic panels), DAT imaging, neuropsychologic testing, and ataxia panel testing (including SCAs, FXTAS, Friedrich ataxia, and Ataxia-Telangiectasia), was unremarkable. There was no family history of dystonia or other movement disorders. Whole exome sequencing revealed gene mutations of the GCH1 and CLCN2 genes. Examination was notable for dysarthria, down-beating nystagmus with leftgaze, weakness with left hip flexion and left shoulder abduction, left-sided bradykinesia, upgoing toe on the left, and inward rotation of the left foot with circumduction and frequent tripping during gait examination. Foot dystonia improved somewhat with baclofen, and oscillopsia improved with dalfampridine. Given that GCH1 has previously been associated with a dopa-responsive dystonia, the patient was given a trial of carbidopa-levodopa, which significantly improved his left-sided stiffness and gait dystonia.

We report a novel dopa-responsive dystonia-Parkinsonism-cerebellar syndrome characterized by progressive hemidystonia, Parkinsonism, and cerebellar dysfunction (oscillopsia, dysarthria) associated with a mutation of the GCH1 gene. Patients presenting with this syndrome may benefit from testing for GCH1 mutation and a trial of dopamine for symptom management.