CSF DOPA Decarboxylase Biomarker Shows Strong Diagnostic Potential for Lewy Body Disorders

A newly developed and validated cerebrospinal fluid (CSF) biomarker for the enzyme DOPA decarboxylase (DDC) shows significant promise for diagnosing Lewy body disorders, including Parkinson's disease and dementia with Lewy bodies. The multicohort study developed two quantitative DDC immunoassays and validated their performance across multiple independent patient groups, finding that CSF DDC levels were substantially elevated in these conditions compared to controls and Alzheimer's disease.

In the clinical validation, CSF DDC levels were significantly higher in patients with dementia with Lewy bodies and Parkinson's disease, reaching up to 2.5-fold levels compared to healthy controls and 1.9-fold compared to Alzheimer's disease patients. The assays demonstrated strong diagnostic accuracy, with area under the curve values exceeding 0.9 for distinguishing Lewy body disorders from other conditions. Models that incorporated CSF DDC concentrations along with patient age and sex showed high accuracy for differential diagnosis.

Analysis across six independent cohorts confirmed that elevated CSF DDC concentrations were consistently associated with Lewy body disorders. In contrast, plasma DDC levels showed no diagnostic value, as blood concentrations did not differ significantly across diagnostic groups and were elevated primarily in patients receiving dopaminergic therapy. The findings indicate that CSF, not blood, is the appropriate specimen for measuring this biomarker.

The biomarker also showed correlations with specific clinical features. In patients with dementia with Lewy bodies, higher CSF DDC levels were associated with the presence of parkinsonian symptoms and visual hallucinations, though not with motor impairment severity. In autopsy-confirmed cases of dementia with Lewy bodies, higher CSF DDC correlated with progressing alpha-synuclein pathology, suggesting the biomarker reflects underlying disease mechanisms.

Immunohistochemical analysis of brain tissue from patients with Parkinson's disease and dementia with Lewy bodies revealed colocalization of DDC and alpha-synuclein in the substantia nigra, providing a potential pathological link. DDC catalyzes the conversion of L-DOPA to dopamine and 5-HTP to serotonin, and elevated CSF levels may reflect dopaminergic neuronal dysfunction or degeneration in these disorders.

While the results support DDC's value as a supportive biomarker for diagnosis and biological characterization of Lewy body disorders, researchers note that further studies are needed to evaluate its performance across broader patient populations and different disease stages. The development of quantitative immunoassays paves the way for potential clinical implementation of this diagnostic tool.