Oprea et al. (2008) studied spinal muscular atrophy-discordant families with affected and unaffected SMN1-deleted siblings and found that all unaffected SMN1-deleted siblings were characterized by a high PLS3 expression level in blood cells, considerably higher than in their affected counterparts (and despite high PLS expression being evident in only 5 % of healthy controls). This evidence concerns the gene SMN1 and proximal spinal muscular atrophy.