We report an original finding of a strong linear correlation (F=26, p=1.5e-4, R2=0.65) between iron accumulation within specific thalamic structures and the age of children with aspartylglucosaminuria (AGU). AGU is a rare lysosomal storage disorder which has no cure, causes a negative effect on the development of a child, and leads to a premature death. We used affine image registration and implemented a voxel-wise permutation test to locate where AGU patients have higher filtered phase SWI intensities (i.e. more iron) than controls. Furthermore, we demonstrated that permutation test was crucial for discovering the linear correlation between iron accumulation and age.