Human loss or gain-of-function mutations in the gene encoding Na<sub>v</sub>1.7 channels (SCN9A) are associated with either absence of pain, as reported for congenital insensitivity to pain, or with exacerbation of pain, as reported for primary erythromelalgia and paroxysmal extreme pain disorder.
We confirm through electrophysiological analysis that this R1488* variant in SCN9A results in complete loss-of-function of Na<sub>v</sub>1.7, which is consistent with reports on other variants in this gene in subjects with CIP.
For example, the voltage-gated sodium ion channel Nav1.7 is expressed selectively in sensory and autonomic neurons; inactivating mutations in SCN9A, which encodes Nav1.7, result in congenital insensitivity to pain, whereas gain-of-function mutations in this gene produce distinct pain syndromes such as inherited erythromelalgia, paroxysmal extreme pain disorder, and small-fibre neuropathy.
In CIP case 6, we identified a novel, de novo splicing mutation (IVS8-2A>G); this splicing mutation compounded with a nonsense mutation (R523>X) and abolished SCN9A mRNA expression almost completely compared with his unaffected father.
Mutations in SCN9A, encoding the alpha subunit of the voltage-gated sodium channel (Nav1.7), have caused severe pain disorders and congenital insensitivity to pain.
Mutations in SCN9A cause three human pain disorders: bi-allelic loss of function mutations result in Channelopathy-associated Insensitivity to Pain (CIP), whereas activating mutations cause severe episodic pain in Paroxysmal Extreme Pain Disorder (PEPD) and Primary Erythermalgia (PE).
Mutations in SCN9A cause three human pain disorders: bi-allelic loss of function mutations result in Channelopathy-associated Insensitivity to Pain (CIP), whereas activating mutations cause severe episodic pain in Paroxysmal Extreme Pain Disorder (PEPD) and Primary Erythermalgia (PE).
These genetic data further support the evidence that Nav1.7 plays an essential role in mediating pain in humans, and that SCN9A mutations identified in multiple different populations underlie CIP.