APOE and Parkinson disease: There is controversy however, from conflicting studies that show a lack of association between cognitive function in PD with the APOE ε4 status (Mengel et al., 2016), which some may have attributed to sex-specific effects due to findings of steeper cognitive decline in male PD patients carrying the ε4 allele that contrasts the lack of interaction in female subjects (Kim et al., 2021a).