A recent study published in Neurology examined the presence of phosphorylated alpha-synuclein (P-SYN) in skin biopsies of individuals with essential tremor (ET) to assess potential co-pathology of ET and prodromal Parkinson’s disease (PD). This study was designed to better understand the prodromal features of PD to improve the assessment of early symptoms of movement disorders.
This cross-sectional cohort study included 65 participants with ET from the Baylor College of Medicine. Researchers characterized patients’ baseline status based on a neurological examination, chart review, and other disease-specific assessments including a tremor rating scale, REM sleep behavior disorder (RBD) questionnaire, and smell testing to determine diagnosis of ET, considered a key prodromal symptom of PD. Skin punch biopsies were performed using the Syn-One Test, with a positive result defined as detection of cutaneous P-SYN in at least one of three biopsy samples. P-SYN biopsy results, taken together with clinical assessments, can help to contextualize P-SYN biomarker findings with the broader clinical picture of ET patients.
The study reports that 37% (24/65) of participants had detectable skin P-SYN, compared with 3.3% in historical healthy controls (p<0.001). The analysis also notes that higher tremor severity scores were associated with increased odds of a positive biopsy. The frequency of prodromal features of Parkinsonian conditions, including REM sleep behavior disorder and reduced olfactory function, were noted to be higher in this study compared to previously reported prevalence in healthy controls.
The authors present these findings as observational data describing the prevalence of the Parkinson’s-related symptoms, cutaneous P-SYN, and other related clinical features within an ET population. The findings suggest that a subset of patients with ET may have features associated with elevated risk for developing comorbid PD, including the presence of cutaneous P-SYN and the high frequency of RBD and hyposmia observed in the study cohort. They also indicated that longitudinal studies are needed to clarify the predictive value of positive P-SYN biopsy results on phenoconversion from ET to PD.
