PRPH and proximal spinal muscular atrophy: They found median serum peripherin levels of 5.376 ng/mL in ALS, 5.653 ng/mL in spinal muscular atrophy (SMA), and 10.224 ng/mL in spinal and bulbar muscular atrophy, compared to 3.168 ng/mL in healthy controls, 1.793 ng/mL in dementia, and 2.21 ng/mL in peripheral neuropathy (PN).