I read recently that there is a link between autism, schizophrenia, and bipolar disorder and some of it is hereditary. I have an autistic son and have suffered severe depression but I am also bipolar and my depression symptoms started long before the birth of my son.
Clinical depression is caused by a chemical imbalance in the brain. Circumstantial depression can be caused by the difficulties of parenting an autistic child.
All parents of special needs children have self esteem issues at some point and need all the reassurance and support they can get.