Schematic diagrams of mutant H alleles found in Bombay and para-Bombay individuals. (A) Partial genomic structure encompassing the open reading frame (ORF) of the H gene. (B) Schematic presentation of the H enzyme. C, TM, SR, and CR indicate cytoplasmic tail, transmembrane domain, stem region, and catalytic region, respectively. (C) The locations of the point mutations found in mutant H alleles. The nucleotide sequence of the active H allele in Japanese population was determined to be the same as that reported by Larsen et al.14