I have often heard it opined that the siblings of children with autism suffer greatly from the extraordinary attention their autistic brothers (and sisters) receive from parents and other relatives. I have often worried that my typical children were being deprived or even damaged as my wife and I work with my youngest son.
Here is a study which addresses part of this, and provides the beginning to an understanding of the dynamics of families with autistic children.
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11902601&dopt=Abstract