Depression in parents with autistic children

Is it common for parents of autistic children to suffer from depression?  We're right at the beginning of our journey to get our 6 year old daughter assessed for ASD, but the SENCO at school is pretty certain she'll get a diagnosis, and of course we have lived for 6 long years with the difficulties and challenges of parenting our daughter.  I am currently signed off work with depression, and whilst I know depression occurs for a complex set of many reasons, I also know that my parenting challenges and the stress of family life are probably the biggest contributors to my current period of depression.  I just wondered if this is a common experience?  Is it 'normal' to feel stressed and end up depressed because of having the particular stresses of ASD to contend with?