SEC23A and Ataxia: Moreover, mutations in the human SIL1 protein cause the Marinesco-Sjögren Syndrome (MSS), which is characterized by mental retardation, ataxia, cataracts, myopathy and skeletal deformities including short stature, a set of symptoms similar to mutations in the COPII component SEC23A [5], suggesting that at least some of the observed abnormalities are due to activation of ER stress response mechanisms.