IGHMBP2 and proximal spinal muscular atrophy: SETX is similar to several genes involved in RNA processing such as the immunoglobulin mu binding protein 2 gene (IGHMBP2), mutations in which are known to cause spinal muscular atrophy with respiratory distress type 1[20], implying that SETX mutations-caused motor neuron degeneration may result from the aberrant RNA processing[21].