CBS and Alzheimer disease: Indeed, animal CβS knockouts are a popular model of HHcy (Troen, 2005; Pacheco-Quinto et al., 2006; Zaric et al., 2019), and a veritable body of literature has demonstrated the strong association between impaired CβS function and AD-associated cognitive decline (Leiteritz et al., 2018; Elsherbiny et al., 2020).