Why the study?
Although SCN9A mutations and phenotypes of painlessness and anosmia/hyposmia are well documented, the complex relationship between genotype and phenotype of congenital insensitivity to pain remains unclear.
Novel SCN9A mutations in a patient with congenital insensitivity to pain retain partial channel function, challenging the notion that total loss-of-function is required for painlessness.
Novel SCN9A variant in CIP case extends mutation spectrum; leaves genotype-phenotype correlations open for functional validation.
Congenital insensitivity to pain (OMIM 243000) is an extremely rare disorder caused by loss-of-function mutations in SCN9A encoding Nav1.7. Although the SCN9A mutations and phenotypes of painlessness and anosmia/hyposmia in patients are previously well documented, the complex relationship between genotype and phenotype of congenital insensitivity to pain remains unclear. Here, we report a congenital insensitivity to pain patient with novel SCN9A mutations. Functional significance of novel SCN9A mutations was assessed in HEK293 cells expressing Nav1.7, the results showed that p.Arg99His significantly decreased current density and reduced total Nav1.7 protein levels, whereas p.Trp917Gly almost abolished Nav1.7 sodium current without affecting its protein expression. These revealed that mutations in Nav1.7 in this congenital insensitivity to pain patient still retained partial channel function, but the patient showed completely painlessness, the unexpected genotypic-phenotypic relationship of SCN9A mutations in our patient may challenge the previous findings “Nav1.7 total loss-of-function leads to painlessness.” Additionally, these findings are helpful for understanding the critical amino acid for maintaining function of Nav1.7, thus contributing to the development of Nav1.7-targeted analgesics.
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Sun et al. (2020) studied this question.
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