PROS1 and juvenile Huntington disease: The production of toxic polymeric repeat proteins by RAN translation has now been characterized in multiple neurodegenerative disorders caused by microsatellite expansions including spinocerebellar ataxia type 8 (SCA8)58, myotonic dystrophy type 1 (DM1)58, Fragile X-associated tremor and ataxia syndrome (FXTAS)59, C9ORF72-ALS6, 13, 14, 15, 16, 27 and Huntington disease (HD)60.