Also, a study on methylation changes in the N-acetylgalactosamine-6-sulfate sulfatase (GALNS) gene involved in MPS IVA showed that transitional mutations that originated after deamination at the CpG dinucleotides were found in 29% of the point mutations in MPS IVA patients, suggesting that methylation in these CpG regions increase the probability of gene mutation5. This evidence concerns the gene GALNS and mucopolysaccharidosis type 4A.