We do know that various rulers (and the population in general) suffered from various ailments and afflictions. However, I think it is quite unrealistic to believe that the Amenhotep IV (Akhenaten) or his family were afflicted with it. Most of the artwork from the period, which was destroyed in ancient times, depicted ALL officials, servants, royals and everyone else from Egypt proper in the same style as Akhenaten himself. Therefore, this does not lend itself to the idea of big hips and other extreme features being synonymous with marfan's syndrome. More likely it was a new style of artistic portrayal, where fat hips and other features were seen as desired traits and a sign of fertility, prosperity and happines. Given that the mummies we do have don't actually provide any evidence for marfan's disease, including the last analysis of Tut's mummy, this must be considered as very unlikely. A good example of the artistic style of exaggerated features can be seen in the reconstructed talatat wall of Akhenaten's temple.