i am no expert in this field and clearly the situation is not a simple one. However for the bulk of patients the hereditary pattern is (from a lay point of view) very much akin to haemophilia i.E the female is the carrier and only boys will be affected when they receive the affected x chromosome from their mother. Non affected boys will not pass on the carrier or affected state. Affected boys can pass their x to daughters who will then be carriers. Sons of carriers will have a 50% chance of being affected depending on which x chromosome they "inherit". The link describes it much better! I have probably committed heresy in the eyes of all geneticists but it seemed that no-one was replying to the query.