The team described a Colombian brother and sister carrying a rare variant in the RELN gene (H3347R coined as RELN-COLBOS after the Columbia-Boston biomarker research study) who showed delayed onset of autosomal-dominant Alzheimer disease despite carrying the PSEN1 E280A mutation known to cause mild cognitive impairment (MCI) by around age 44 and AD type dementia by age 49.1 This evidence concerns the gene PSEN1 and Alzheimer disease.