MRPL9 and major depressive disorder: In order to further narrow down and improve the screening of key genes, eight genes screened by four algorithms of cytoHubba were intersected with 26 key genes calculated by Lasso regression, and finally the intersection of disease-specific markers revealed three shared diagnostic markers for OSA with comorbid MDD: CD74 (CD74 molecule), RPL26L1 (ribosomal protein L26 like 1), and MRPL9 (mitochondrial ribosomal protein L9) (Figure 7E).