After Bonferroni correction, stratified GNOVA analyses highlighted significant negative genetic covariance between AD and obesity through the Reactome INSR recycling gene set (p = 4.6 × 10−5), as well as between ASD and MetS through the Biocarta, KEGG, and PID insulin signalling pathways (p ≤ 3.2 × 10−5). This evidence concerns the gene INS and Alzheimer disease.