PSEN1 and Down syndrome: Recent studies have identified some genetic predispositions (just as consanguineous marriage, maternal telomere length, maternal MCM9 polymorphisms, maternal Presenilin-1 and Apolipoprotein E polymorphisms) of women that may cause nondisjunction and Down syndrome birth at younger age (Ray et al., 2016; Bhaumik et al., 2017; Ray et al., 2018; Pal et al., 2021).