TREM2 and dementia: One DS participant (D4, 39 years old) with TREM2 R47H (T allele) who was heterozygous for ApoE (ɛ3/ɛ4) slowly deteriorated and developed dementia, whereas another DS participant (D7, 37 years old) who was homozygous for ApoE (ɛ3/ɛ3) but had no clinical symptoms of dementia as yet.