People with disabilities are labelled as a "group" of people with specific special needs both physically and mentally. They have specific learning and physical support needs that need specialization aid. In society and in an education environment their needs have to be supported appropriately in order for them to feel as accepted individuals in society!
In some way or the other we have all been faced with an impairment albeit it mental, physical, emotional, psychological. The challenges are unique to each and every individual. Thus you cannot categorize impairment to a certain group of people but perhaps one can categorize people to a certain group of impairment, example the physical handicapped, blind, deaf, etc.
This question is ridiculous when we really think about it why would one even pose such a question. We are all human beings in the long run and can be effected by the same thing. Not one certain group will only be effected by something. Also what exactly is a certain group?
Different impairments have different methods of transmission. Some are genetic, some are birth injuries, some are environmental and many are a combination thereof. Genetic issues include both inherited issues and de novo conditions, which are new mutations in that generation, so even a genetic issue does not mean that it came from the family line. With so many factors, it is impossible to say that an impairment affects just one group of people.