How does Christopher hurt his mother?

One of the most devastating moments in the novel is when Christopher refuses to let his mother hold his hand. She hasn't seen her son for two years, and he has just survived a truly terrifying voyage to reach her. And yet she cannot satisfy her maternal instinct to cuddle him. She cannot even hold his hand. Most people express their love through touch, but Christopher is incapable of this emotional experience, even as he understands it rationally. Therefore, those who truly love him, like his mother, are forced to work within his comfort range. And so the mother cannot hold her child. This moment vividly captures the difficulty of raising a differently-abled child.