I thought that ALD only affects boys. Is it rare/possible for young girls to be diagnosed with ALD?

The gene that causes ALD appears on the X chromosome; women are carriers of two X chromosomes, while men have one X and one Y chromosome. If a girl has one X chromosome with the ALD mutation, she can pass the disease along to her sons. She will not usually have the disease herself, but sometimes will show some mild symptoms, such as motor difficulties. This usually only appears in adult women.