Sexual feelings are normal, and there are many ways of expressing one's sexuality.
If a person has a disability, it does not change any of this. What often changes is the socialization that provides the foundation for sexual identity. In America, people with disabilities are sometimes oppressed and treated as less than someone without an identifiable disability. This can have a profound impact on the individual's self-identity. Often, people with developmental disabilities feel they are bad or that something is wrong with them.