HSPB1 and distal hereditary motor neuropathy: Furthermore, the mRNA levels were normal or higher than normal in both cell lines, suggesting that posttranslational degradation mechanisms may be responsible for the absence of the IGHMBP2 protein and a correlation between the phenotype and the quantity of residual protein has therefore been hypothesized.24 Moreover, the function of IGHMBP2 is similar to that of GARS, AARS, HSPB1 and HSPB8, which have all been associated with both CMT and distal hereditary motor neuronopathy (dHMN) phenotypes.