It might be intriguing as to why effects of the MPS IVA and IVB disease on the cleavage of caspase-9 at two different positions, Asp315 and Asp330, are different (Figure 2; a lack of differences between control cells and MPS IV fibroblasts in the case of the cleavage at Asp315 and significant differences in the case of that at Asp330). The gene discussed is CASP9; the disease is mucopolysaccharidosis type 4A.