Analysis with the HSP assay revealed reduced expression of alpha 2-antiplasmin (p = 0.0182 – 0.0353), immunoglobulin heavy constant alpha 1 (p = 0.014 – 0.0245), and antithrombin III (p = 0.033 – 0.045) in the cases but not in the controls (p = 0.5–0.9). This evidence concerns the gene IGHA1 and hereditary spastic paraplegia.