Upon performing regression analysis, which could reflect the possible causal correlation between serum prolactin level (ng/ml) (the predictor) and CAL as well as PD measurements (mm) (the outcome), results yielded a statistically significant direct relation (P = 0.002, 0.001, respectively), which indicates that an increase in serum prolactin level could possibly cause an increase in CAL and PD measurements, which are the main indicator for diagnosis and severity of periodontitis, as well as PD measurements, as shown in Table 5. This evidence concerns the gene PRL and Parkinson disease.