Protein subunits encoded by WT and mutant alleles for a heterozygous mutation could potentially assemble into five different stoichiometries of tetrameric BK channels and six different subunit arrangements. See MacKinnon, 1991; Blaine and Ribera, 1998; Ding et al., 1998; Niu and Magleby, 2002; Bergendahl et al., 2019. In this diagram, WT and mutant alleles (gene) encode for WT and mutant protein subunits (protein subunit), which then assemble into tetrameric assembled channels with five different subunit stoichiometries and six different subunit arrangements (assembled channels). The listed theoretical percentages of expression of the five different stoichiometries of assembled channels were calculated with Eq. 2, which assumes that equal numbers of mutant and WT subunits randomly assemble into tetrameric channels, each with equal probability of reaching the surface membrane. With random assembly, ∼6% of the assembled channels are WT comprised of four WT subunits per channel, ∼88% are hybrid (mixed subunit) channels with from one to three mutant subunits per channel, and ∼6% are homotetrameric mutant channels comprised of four mutant subunits per channel. Note that ∼94% of the assembled channels can be pathogenic, as they contain from one to four mutant subunits per channel. The listed percentages of ∼6, ∼38, and ∼94% here and throughout the paper have been rounded from the calculated values of 6.25, 37.5, and 93.75%, respectively. The 37.5% reflects the sum of 25% for hybrid channels with two adjacent mutant subunits and 12.5% for hybrid channels with two diagonal mutant subunits (Bergendahl et al., 2019). For experimentation, assembled channels are those channels expressed following injection of a 1:1 mixture of mutant and WT cRNA into Xenopus oocytes to mimic a mutation in which the mutant allele is heterozygous with the WT allele.