Additionally, it appears that the proteins identified by clustering analysis and proteins whose expression is consistent in other neurodegenerative diseases (i.e. citrate synthase—CS in SMA) or correlate with vulnerability status (i.e. cathepsin d—CTSD in Wlds; see Fig. 5) all share a common upstream regulator—APP. The gene discussed is CTSD; the disease is proximal spinal muscular atrophy.