GNAS and autosomal dominant cerebellar ataxia: However, the diagnosis of SCA can be made based on the absence of other markers, for example, the absence of the CTNNB1 mutation, which is specific for solid pseudopapillary, lack of KRAS or GNAS mutations, being specific for a mucinous cyst, as well as the use of other advanced endoscopic techniques to characterize the vascular network of the cyst walls.