a Salivary Cell-free RNA Liquid Biopsy Model for Non-invasive Diagnosis in Sjögren's Disease

The goal of this observational study is to learn whether salivary cell-free RNA (cfRNA) can be used as a non-invasive liquid biopsy test to help diagnose Sjögren's disease (SjD) and understand disease-related changes in the salivary glands. The main questions it aims to answer are: * Can salivary cfRNA distinguish patients with SjD from people with sicca symptoms who do not have SjD? * Are salivary cfRNA signals associated with clinical features of SjD, such as autoantibody-related immune activity and salivary gland pathology? * Can salivary cfRNA signals be linked to specific cell types and tissue regions in the salivary glands? Participants will provide saliva samples, and clinical information from routine medical evaluation will be collected. Some available salivary gland tissue transcriptomic data will also be analyzed to explore the possible tissue sources of salivary cfRNA signals.

Inclusion Criteria: SjD group: * Aged 18-65 years * Fulfilled the 2016 ACR/EULAR classification criteria for Sjögren's disease * Newly diagnosed or previously diagnosed with complete diagnostic evidence available * Willing to provide clinical data and saliva samples * Provided written informed consent Non-SjD sicca control group: * Aged 18-65 years * Frequency-matched with the case group by sex and age * No personal or family history of autoimmune diseases * No persistent symptoms suggestive of SjD (e.g., dry mouth or dry eyes), with physical examination and necessary laboratory test results within normal limits * Willing to provide clinical data and saliva samples * Provided written informed consent Exclusion Criteria: * Malignant tumors or severe active infections * Pregnancy or lactation * Use of biologics or potent immunosuppressive therapy within the past 3 months that could significantly alter study indicators (patients included due to strict clinical necessity will be recorded and utilized for sensitivity analysis) * Severe hepatic or renal impairment, or other diseases that significantly interfere with cfRNA detection * Failure to meet the standardized oral status, fasting, or sampling timing requirements prior to collection, with resampling being impossible * Incomplete clinical data * Substandard collection, preservation, or quality control of saliva or labial gland tissue samples * Any other conditions deemed unsuitable for participation by the investigator