Mutations in the SCN9A or SCN10A gene can cause small fiber neuropathy. These genes provide instructions for making pieces (the alpha subunits) of sodium channels. The SCN9A gene instructs the production of the alpha subunit for the NaV1.7 sodium channel and the SCN10A gene instructs the production of the alpha subunit for the NaV1.8 sodium channel. Sodium channels transport positively charged sodium atoms (sodium ions) into cells and play a key role in a cell's ability to generate and transmit electrical signals. The NaV1.7 and NaV1.8 sodium channels are found in nerve cells called nociceptors that transmit pain signals to the spinal cord and brain.