SMN1 and proximal spinal muscular atrophy: In the present study, homozygous absence of SMN1 exons 7 & 8 in association with deletion of NAIP exon 5 were found in most type I patients (16/30; 53.3%) and in smaller percent in type II (8/35; 22.9%) SMA patients the distributions of SMN1 copy number were 0.