What's the probability of someone being intolerant to lactose and gluten?

Not just lactose: Gluten intolerance is more common than we think and is often associated with other food intolerances. Lactose intolerance is just one possible way a person can react to milk products but often someone with gluten intolerance is also intolerant to the actual milk proteins, like whey or casein (and not just the milk sugar, lactose). There are some tests available that can help determine the problem.