APOE and Alzheimer disease: APOE-ε4, a widely-accepted AD risk factor68, was also indicated as an important feature, as both “APOE x/ε4” (i.e., ε2/ε4, ε3/ε4, ε4/ε4) and “APOE ε4_number” (i.e., pairwise or not) showed large SHAP values.