The regulatory relationship between rs12442183 and RGMA expression was studied using publicly available microarray data. RGMA encodes a glycosylphosphatidylinosital-anchored glycoprotein (RGMa). There are three RGMa isoforms (Supplementary figure 3) that are generated by six RGMA transcript variants (Figure 3A), including NM_001166283 (variant 1), NM_001166286 (variant 2), NM_001166287 (variant 3), NM_020211 (variant 4), NM_001166288 (variant 5) and NM_001166289 (variant 6). Transcript variant 1 and 4 encode RGMa isoforms 1 and 3, respectively, and all other transcripts produce the same RGMa isoform 2. To identify alternative expression of RGMA among 11 healthy human tissues, four RGMA exons, including ENSE00001325239, ENSE00001319132, ENSE00001304160 and ENSE00001532613, were analyzed via R package ESLiMc (Figure 3A). ENSE00001325239 and ENSE00001319132 reside in the overlapping exonic regions in all 6 transcripts of RGMA, i.e., the expression signals of the two exons represent the total mRNA of RGMA. ENSE00001532613 is a specific exon representing transcript variant 4 (NM_020211, encoding RGMa isoform 3). Similarly, exon ENSE00001304160, specifically represents transcript variant 2 (NM_001166286, encoding RGMa isoform 2). Only ENSE00001532613, representing transcript variant 4, was variably expressed among the 11 tissues studied, and
