It began when the couple requested personal information about Eamon including emails between the HDC and disability provider IDEA Services, which the Chief Ombudsman recommended should be released.
The Privacy Commissioner warned the HDC it would be in breach of the Health Information Privacy Code if it did not release the emails.
Throughout the protracted process the HDC tried to limit Marshall's requests for official information, hired external lawyers to fight the case and refused to add a correction to its decision on Eamon's care.
At one stage Health and Disability Commissioner Anthony Hill tried to meet with Privacy Commissioner John Edwards to discuss the case.
Marshall claimed this was "highly inappropriate", saying it ran the risk of being seen to exert undue influence on the independence of the Privacy Commissioner.
The HDC put a warning out on Marshall to its staff, calling his conduct for numerous requests for information unreasonable.
It also asked the Privacy Commissioner to reconsider the breach finding against it, but it did not.
Marshall has called for an investigation into the HDC but Health Minister Dr David Clark said he could not comment or intervene.
Marshall said he HDC was not open and transparent and appeared to favour providers over patients.
The 49-year-old wants to end what he calls an "abuse of power" and bring about meaningful change. And he wants better appeal rights to HDC decisions.
"This is a story about how we treat our most vulnerable people."
He and Fran Marshall, 48, are claiming $300,000 in total for their son's significant humiliation and loss of dignity.
Hill said he could not comment on the case because of the legal proceedings but stood by the HDC's output saying it closed 2392 complaints last year.
More than half of those ended with "no further action".
Only 4 per cent of complaints to the HDC, about 80 to 100, are investigated and some take years to conclude.
Hill said complainants have a right of appeal through the Ombudsman, which is free, or at judicial review in the High Court.
Auckland University Professor Jo Manning called the case exceptional and said the HDC "has a few questions to ask of itself".