AMY1 gene copy number associated with xerostomia and Sjögren's syndrome: a cross-sectional study

Dry mouth-related conditions adversely affect patients' well-being, as well as their oral and general health. There are indications that the quantitative and qualitative protein composition of saliva is disrupted in patients with xerostomia and Sjögren's syndrome. Salivary α-amylase levels positively correlate with the copy number (CN) of its coding gene, AMY1 (amylase alpha 1). This study aimed to investigate the association between intensity of xerostomia, Sjögren's syndrome, and AMY1 CN. Establishing such an association could position AMY1 CN as a potential genetic biomarker for dry mouth-related conditions, aiding in their early detection.

This cross-sectional study utilized secondary data from the main dry mouth study conducted in five public hospitals in Vilnius, the capital city of Lithuania. Based on sample size calculations for the main study, 127 patients who met the inclusion criterion of dry mouth complaints (sometimes, often, and always) were recruited. The outcomes were xerostomia intensity, assessed using a visual analogue scale (VAS), and confirmed cases of Sjögren's syndrome, assessed using the 2016 ACR/EULAR classification criteria and classified as either primary or secondary. Sociodemographic information included age and sex; self-perceived stress levels were assessed using the Perceived Stress Scale (PSS-10). During clinical examinations, unstimulated whole sialometry was performed for 15 min, and oral mucosa swabs were collected. The swabs were used to quantify AMY1 CN via droplet digital PCR (ddPCR). Data were analyzed using both univariable and multivariable regression models.

In total, 112 patients with available AMY1 CN data and recorded xerostomia intensity VAS scores were included in this study. Of these, 26 (23%) were diagnosed with Sjögren's syndrome; 9 (8%) had primary and 17 (15%) had secondary Sjögren's syndrome. According to multivariable linear regression analyses, higher AMY1 CN was associated with 0.15 lower xerostomia intensity VAS score (β =-0.15, 95% CI -0.30, -0.01). Higher AMY1 CN reduced the odds for primary Sjögren's syndrome (OR 0.52, 95% CI 0.03-0.89).

The present study indicated an inverse association between xerostomia, primary Sjögren's syndrome, and AMY1 CN. Studies validating these findings and exploring the underlying mechanisms are warranted.