SCN9A and paroxysmal extreme pain disorder: While missense mutations in Nav1.7 have been found in most families with IEM and PEPD in whom the gene was sequenced, both IEM and PEPD may be genetically heterogenous because mutations in the coding exons of SCN9A were not found in 5 cases of PEPD [19], or in cases of familial early-onset [30] and adult-onset IEM [31], suggesting that other target genes or mutations in non-coding regions of SCN9A might underlie these cases.