In contrast, studies of a spontaneously arising model of SMA with respiratory distress, the neuromuscular degeneration (nmd) mutant mouse, showed that, whereas transgenic expression of Ighmbp2 in neurons was sufficient to correct the motor neuron degeneration in the mice, they subsequently developed skeletal myopathy and dilated cardiomyopathy. Here, IGHMBP2 is linked to proximal spinal muscular atrophy.