Personal Opinion: Intelligence and Grades are two different things. Depression may make it difficult or impossible to display your intelligence through obtaining high grades, but it rarely diminishes your true, essential intelligence.

The grades one earns in school are but symbolic achievements. Their value is in spurring one to efforts and habits that eventually will shape one into "a productive member of society". Unfortunately, for some, grades/marks can become a drug delivering diminishing returns, or a carrot to pursue - and in the end we may find that we've been strenuously pulling a cart full of others' dreams and not our own.

Consider this for a moment: insofar as your depression interferes with your "success" as a student, it may force you to find passions and talents truly your own. If you find them, you may end up creating real happiness for others and yourself far beyond what you would have following a more conventional path.

The very best to you!