Hello @katec, I have idiopathic small fiber PN diagnosed by a Mayo neurologist and think mine maybe heriditary but without extensive testing on others in the family I don't think there is anyway for me to know. I hope you can find the cause and something that helps your son. Hoping other members who have been diagnosed with idiopathic SFN will be able to offer some suggestions. It's good to see that you are learning as much as you can about his condition. I think that the more knowledge you have the better questions you can ask the doctors and hopefully have a better treatment for your son.

The National Institute of Health has a fact sheet that lists a lot of causes along with other information that you might find helpful if you have not already seen it.
-- https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Peripheral-Neuropathy-Fact-Sheet#183563208

Also the Neuropathy Commons website is one of the better resources for information - https://neuropathycommons.org/