We give them so much metal early in life, specifically through the hepatitis B vaccine given at birth, that their bodies keep producing metallothionein, which is what helps us to remove metals from the body. After their biochemistry is depleted, they end up with an inability to handle any metal at all.  Biochemist Bill Walsh of the Pfeiffer Treatment Center made this discovery. He tested 503 autistic children and found that 91 percent had a deficiency of metallothionein, whereas normal children do not. [2002] Balancing Biochemistry: An Interview with Stephanie Cave