Short tandem repeats (STRs) are a common type of genetic variation within the human genome and are defined as DNA segments composed of tandemly repeated nucleotide motifs that are usually 2-6 base pairs in length.1-3 STRs can undergo changes in length, usually an increase in the number of tandem repeats due to various biological processes, making them unstable.1-3 This instability at specific loci can lead to genetic disorders, collectively known as repeat expansion disorders (REDs).4 Over 50 REDs, many of which cause neurological disorders, have been associated with expansion of STRs or variable number tandem repeats (VNTRs: ∼7-100 bp motifs) (Table 1).