Differential Diagnosis
A dramatic and sustained response to low doses of levodopa in dopa-responsive dystonia (DRD) distinguishes this disorder from cerebral palsy, spastic paraplegia, and all other forms of dystonia, including early-onset primary dystonia (DYT1). (For a differential diagnosis of dystonia, see Dystonia Overview.) The major differential diagnoses of GTPCH1-deficient DRD are summarized in and include TH-deficient DRD, SR-deficient DRD (rare), and early-onset Parkinson disease. Table 2. Disorders to Consider in the Differential Diagnosis of GTPCH1-Deficient DRD
DiffDx Disorder | Gene(s) | MOI | Clinical Features of DiffDx Disorder |
|---|
Overlapping w/GTPCH1-deficient DRD | Distinguishing from GTPCH1-deficient DRD Tyrosine hydroxylase-deficient DRD (DYT5b; DYT-TH) | TH1 | AR |
SPR | AR4 | 1 family reported w/strikingly mild sepiapterin reductase deficiency phenotype (DRD w/o motor cognitive delay)5,6; Sepiapterin reductase deficiency w/mild findings may mimic GTPCH1-deficient DRD.; Remarkable response to levodopa; Diurnal fluctuation of symptoms | concentration of BP is assoc w/nl concentration of NP in CSF.2 |
Manifestations of DYT-SPR typically begin earlier than those in GTPCH1-deficient DRD. Early-onset Parkinson disease(See Parkin Type of Early-Onset Parkinson Disease, PINK1 Type of Young-Onset Parkinson Disease, and Parkinson Disease Overview.) | PINK17PRKN8 | AR | In the early course, the clinical differentiation between early-onset Parkinson disease w/dystonia GTPCH1-deficient DRD is difficult.; Persons w/early-onset Parkinson disease (esp those w/onset age 20 yrs) often develop gait disturbance (attributable to foot dystonia) as the initial symptom.9 |
Source: GeneReviews — "GTP Cyclohydrolase 1-Deficient Dopa-Responsive Dystonia"
