Transcranial sonography in dopa-responsive dystonia

Mutations in the GCH1 gene, encoding GTP cyclohydrolase 1, the enzyme critically important for dopamine production in nigrostriatal neurons, are the most common cause of dopa-responsive dystonia (DRD), characterized predominantly by limb dystonia, although parkinsonian features may also be present. It has been suggested that DRD is a neurochemical rather than neurodegenerative disorder.

Transcranial brain sonography, which might be a risk marker for nigral injury, was obtained from 141 subjects divided into four groups: (i) 11 patients with genetically confirmed DRD; (ii) 55 consecutive patients with Parkinson's disease (PD); (iii) 30 patients diagnosed as isolated adult-onset focal dystonia; and (iv) 45 healthy controls (HCs).

Substantia nigra hyperechogenicity was present in 63.6% of patients with DRD, which was significantly different in comparison to patients with dystonia (20%) and HCs (6.7%), but not in comparison to the PD group (87.3%). Also, values of the maximal areas of substantia nigra hyperechogenicity in patients with DRD were higher in comparison to HCs, but significantly lower than among the PD group.

We suggested that the observed transcranial brain sonography features in patients with DRD might primarily be risk markers for particular clinical features (parkinsonism, dystonia) occurring in the specific genetic context (i.e. GCH1 mutations), or might reflect compensated neurodegenerative processes triggered by the long-lasting dopamine deficiency due to the profound delay in levodopa treatment in our patients with DRD.