The most commonly considered confounders across studies include genetic and demographic variables (such as age, sex, ethnicity, and APOE status), comorbidities (including diabetes, hypertension, hypercholesterolemia, cardiovascular disease, and obesity), conditions affecting blood cell counts (such as infectious diseases, rheumatic immune diseases, cancer, and stroke), lifestyle factors (such as smoking and alcohol consumption), and protective factors associated with brain health (such as education and physical activity). The gene discussed is APOE; the disease is obesity due to melanocortin 4 receptor deficiency.