 These cerebellar signs result in a phenotypic overlap between FHM and both episodic ataxia and spinocerebellar ataxia.This is unsurprising as subtypes of these disorders (FHM1, EA2 and SCA6) are allelic, i.e., they result from mutations in the same gene.The other forms of FHM seem to be distinguishable only on the basis of their genetic cause.