The risk factors of cognitive disorder consist of age, gender, smoking, alcohol drinking, obesity, hypertension, chronic heart disease, diabetes, metabolic syndrome, stroke, hypothyroidism, active psychiatric drug, apolipoprotein E epsilon 4 (APOE ε4) allele, Down syndrome, abnormal maxillofacial anatomy, family history, and OSA [54]. Here, APOE is linked to obstructive sleep apnea syndrome.