Mercury is known to disable the enzyme that we need to handle such things. So many autistic kids have this problem because mercury is an underlying factor in at least some of their symptoms. In addition to diet, there are enzymes that can be taken to help. I think houston enzymes has one, also everythingspectrum.com.
Be smart about what you take to detox. Kicking up HMs is dangerous. Just because something is "natural" it does not mean it is safe to take randomly, especially in sickly people. Furthermore many people who have an HM problem don't tolerate foods and supplements that contain lots of sulfur/thiols. The issue of messed up transsulfuration is complex and often not easy to fix.