Trimodal HMOX1 (GT)_n repeat distribution among 942 participants with SCD in the SIT Trial. Allele lengths were scored as number of dinucleotide repeats and ranged from 13 to 45 repeats. Individual (GT)_n alleles assigned to −413 T (gray bars) or A (black bars) chromosomes by PHASE 2.1 haplotype estimation. Initial analyses were performed by grouping observed HMOX1 (GT)_n repeat sizes into 2 allele classes: short (S) with ≤ 25 repeats and long (L) with > 25 repeats.