Spinocerebellar ataxia type 15/16 (SCA15/16) is a rare subtype of type I autosomal dominant cerebellar ataxia (ADCA type I; see this term). It is characterized by cerebellar ataxia, tremor and cognitive impairment.

Cerebellar ataxia refers to ataxia due to dysfunction of the cerebellum. This causes a variety of elementary neurological deficits including asynergy (lack of coordination between muscles, limbs and joints), dysmetria (lack of ability to judge distances that can lead to under- oder overshoot in grasping movements), and dysdiadochokinesia (inability to perform rapid movements requiring antagonizing muscle groups to be switched on and off repeatedly).