Why people get sick:

"There is only one genetic difference between A1 and A2 milk, being the amino acid at position 67 in the chain of 209 amino acids that make up beta-casein protein in milk. “In the case of A1 beta-casein the amino acid at position 67 is histidine, whereas with A2 beta-casein it is the amino acid proline.”"   -- Devil in the Milk, Craig Potton Publishing, Nelson, 2007, page 37