Additionally, specific key genes involved in muscle function and calcium-ion handling (1.8-fold enrichment, p value 1.6E−04) are lower (Atp2a2, Casq1, CaBP1, S100a10, Rcan1, and Hrc) and higher in transcript level (Scin, Efhd2, and Myom2) in heart tissue of SMA mice as compared to unaffected mice (Fig. 3b). Here, HRC is linked to proximal spinal muscular atrophy.