From a recent review of mutations for MPSIVA (MIM:253000) (Tomatsu et al. 2005), almost 80% of mutations in N-acetylgalactosamine 6-sulfatase (GALNS; MIM:612222) were missense mutations and of these, the most common ones are R386C, G301C and I113F.
Tranda Firescu, GG,
N-acetylgalactosamine-6-sulfatase activity of GALNS mutants [lysosomal lumen]
Loss of function of GALNS mutants [lysosomal lumen]