SYNJ1 and Down syndrome: In addition to specific mutations in SYNJ1, trisomy at the locus 21q22.11 containing SYNJ1 gene has been identified in multiple lymphoblastoid cell lines developed from individuals with Down syndrome; these cells show enlarged endosomes as a result of overexpression of SYNJ1 in these cells (Cossec et al., 2012), indicating a link of SYNJ1 to Down syndrome.