Statistical Analysis
We described data as mean (standard deviation) or number (percentage) for continuous and categorical variables, respectively. We employed the Student t-test and Chi-squared or Fisher’s exact tests to compare continuous and categorical variables between the study groups, respectively. For calculating odds ratio (OR) and 95% confidence interval (CI), we fitted a binary logistic regression model to the data. In the case group, we fitted a linear regression model to the data for predicting serum vitamin B12 in these patients. We included age, sex, TSH, and the frequency of lifetime syncopal episodes (≥3 versus <3 episodes) as independent variables in the model. All analyses were done using R version 4.0.3 (2020-10-10). The significance level was set at 0.05 with two-sided tests for all hypotheses.