Spinal muscular atrophy (SMA) as a prototype is an excellent example, where, the majority of SMA patients are homozygous for SMN1-exons 7-8 deletion; however, phenotype severity is directly influenced by SMN2 (SMN1 pseudogene) copies that determine SMA subtype and can ameliorate the SMA phenotype [38]. The gene discussed is SMN2; the disease is spinal muscular atrophy.