We simulated heterozygous C9ORF72 STR references composed of two alleles along with 2X1000bp flankings: one with a normal C9ORF72 STR repeat size (62bp including 18bp perfect repeat units), and the other with a very large expansion in the range commonly found in humans with ALS or FTD (about 100 repeat units longer than reference). The gene discussed is C9orf72; the disease is amyotrophic lateral sclerosis.