It seems as if they might be similar in thinking but are they the same thing? justaskin
They are very much different.
Total depravity posits that humans cannot generate a goodness in and of themselves that would meet God's standard of holiness. It sees humanity as having a corruption that fundamentally flaws the human character. Similar to cancer, sin pervades every area of the human being so that a person cannot be righteous by their own efforts or please God by their own efforts.
Gnosticism is the belief that the body is merely a vessel and the spirit of a person is all that matters. You could do anything you want with your body as it is meaningless. Sin to your hearts content with your body because it's just a holding spot for your soul. Feed your hedonistic desires because it's just your body and your body is of no value. The book of Jude as well as John's three letters all address the gnostic beliefs found in the early church. Paul's comment about sin in Romans 6 addresses the abusive thinking of gnostics.