The results showed that PCDH9 (rs9540720) (ORGG+GA = 2.33, 95% CI: 1.35–4.02) and NPTs (OR5–9 = 2.26; 95% CI: 1.40–3.64) were significantly associated with MDD in first-year university students (Table 5). This evidence concerns the gene PCDH9 and major depressive disorder.