Alpha-synuclein levels in the gut are linked to Parkinson’s disease, indicating that gut alpha-synuclein may be used in combination with other disease biomarkers to facilitate patients’ diagnosis, a review study found.
The study, “Diagnostic utility of gut α-synuclein in Parkinson’s disease: A systematic review and meta-analysis,” was published in Behavioural Brain Research.
Parkinson’s disease is associated with the overproduction of the protein alpha-synuclein in nerve cells of the brain. When this protein clumps together, it gives rise to small toxic deposits inside brain cells, called Lewy bodies.
Alpha-synuclein phosphorylation — a chemical modification in which a phosphate group is added to the protein — is known to occur in Parkinson’s disease, and is thought to be a critical step in disease progression as it enhances alpha-synuclein’s toxicity, possibly by increasing the formation of alpha-synuclein aggregates.
Some scientists think Lewy bodies form in the enteric nervous system (ENS) — the network of nerves that innervate the gastrointestinal tract — then spread to the brain, where they will gradually damage and destroy brain cells.
Although alpha-synuclein has already been detected in tissue samples collected from the stomachs and colons of Parkinson’s patients, its usefulness as a disease biomarker is still controversial.
Chinese researchers conducted a systematic review focused on assessing the relationship between gut alpha-synuclein and Parkinson’s, as well as its diagnostic power in distinguishing patients with the disease from those without it (controls). They reviewed 21 previously published studies reporting findings on gut alpha-synuclein, or phosphorylated alpha-synuclein.
Pooled data from the studies revealed that patients with Parkinson’s were approximately 10 times more likely to have deposits of alpha-synuclein in the gut compared to control subjects. This suggests a direct relationship between gut alpha-synuclein and Parkinson’s disease.
Further analysis showed that gut alpha-synuclein and phosphorylated alpha-synuclein could correctly identify 81.9% and 82.2% of individuals who did not have Parkinson’s disease. However, both had poor sensitivity and failed to distinguish patients with the disease from control subjects in approximately half the cases — a sensitivity of 56.8% for gut alpha-synuclein and 57.9% for phosphorylated alpha-synuclein.
“These results showed that a single measurement of gut [alpha]-synuclein could lead to the underdiagnosis of Parkinson’s disease,” researchers said. “This systematic review and meta-analysis confirmed a high degree of association between gut α-synuclein and Parkinson’s, which suggested that gut [alpha]-synuclein is a potential therapeutic intervention.”
Additional studies are still warranted to further explore the diagnostic potential of gut alpha-synuclein when combined with other biochemical markers of the disease, and “more efforts should be made to improve the standardization of current assays,” they said.