Fig. 1: Generation of a panel of polymorphic STRs.
From: Polygenic burden of short tandem repeat expansions promotes risk for Alzheimer’s disease
a Schematic of study design. Middle section shows six example STRs (STR1-6), with rows representing STRs, columns representing individuals, and numbers representing non-reference STR tract lengths. Long expansions are bolded. STR1 is an example of a rare STR expansion seen only in individuals with AD. At the bottom are three models for testing for associations with AD case/control status. In model 1 (left), STR tract lengths are treated as a continuous variable. In model 2 (middle), STR expansions are defined as those longer than a given STR tract length threshold, and we compare the number of individuals with a given STR expansion between AD cases and controls. In model 3 (right), we identify rare, long STR expansions, and we compare the number of such STR expansions per individual across the genome between cases and controls. b Genomic distribution of STR panel. c Histogram of repeat unit lengths (number of base pairs [bp] in STR motif) for STR panel. Inset shows the subset of STRs with repeat units 7 bp or longer. d Histogram of STR tract lengths (number of repeat units) in the GRCh38 reference genome for each STR in the panel. e Histogram of median STR tract lengths relative to the GRCh38 reference genome as genotyped by ExpansionHunter. Negative values indicate a shorter median STR tract length relative to reference genome and positive values indicate longer median tract lengths relative to reference genome.
