Rare disease is diagnosed in a small population group; it is most often assumed to affect 1 in 2000–2500 people. Depending on its course, the age of manifestation, the presence of a period of regression, stabilization, motor, cognitive, and speech development may proceed individually. Children with rare disease are often diagnosed with individualized educational needs and complex communication needs. Complex communication needs are experienced by someone with problems with sending, understanding, or receiving verbal speech. It will be significant whether damage to the nervous system responsible for, among other things, cognitive processes and speech broadcasting has occurred because of the disease. In the case of intellectual disability, complex learning needs will be associated, for example, with difficulties in forming correct phonological structures. Other co-occurring symptoms, such as apraxia, will also mask them.