SPAST and Motor neuron atrophy: In addition, various syndromes of motor neuron degeneration are caused by mutations in other genes such as Progranulin/GRN[15], Angiogenin/ANG [16], CHMP2B[17], Spastin/SPAST[18], PRPH [19], VAPB [20], and Alsin/ALS2 [21].