EEA1 and trisomy 21: In cells with and without trisomy 21, the extent of colocalization of FcRn with the endosomal marker EEA1 was ~ 40% (PCC DS: 0.40 ± 0.10, PCC NDS: 0.43 ± 0.12), and the extent of colocalization of FcRn with LAMP1 was ~ 10% (PCC DS: 0.10 ± 0.05, PCC NDS: 0.09 ± 0.03).