SMN1 and proximal spinal muscular atrophy: There are many case studies reporting the co-occurrence of SMA and ALS within a family (Appelbaum et al., 1992; Camu and Billiard, 1993; Orrell et al., 1997; Corcia et al., 2002a) which suggests that SMN1 deficiency may lead to ALS in addition to SMA.