Autosomal dominant cerebellar ataxia type I: A review of the phenotypic and genotypic characteristics

Autosomal Dominant Cerebellar Ataxias, Spinocerebellar ataxias.The definition of spinal cerebellar ataxias (SCAs) despite significant progress in their understanding is still imprecise. They can be divided by the mode of inheritance to autosomal dominant, autosomal recessive, or sporadic conditions, Harding proposed a classification of autosomal dominant cerebellar ataxias (ADCA) into three categories, Type I, Type II and Type III. ADCA Type I comprises syndromes such as SCA1- SCA4, SCA8, SCA10, SCA12 - SCA23, SCA25, SCA27, SCA28 and DRPLA. ADCA Type II comprises syndromes associated with pigmentary maculopathies and includes SCA7. ADCA Type III comprises pure cerebellar syndromes and includes SCA5, SCA6, SCA11, SCA26, SCA29, SCA30 and SCA31 [1].The ADCA Type I are the subject of this review. ADCA Type I contain at the time of this writing a group of 22 disorders. There are no fully validated diagnostic criteria for ADCA Type I. The diagnosis is based on clinical history, physical examination and genetic testing.Phenotypes of ADCA Type I are complex and include ataxia plus other neurological signs. The clinical spectrum ranges from just "pure" cerebellar signs to constellations including spinal cord syndromes, peripheral nerve disease, cognitive impairment, cerebellar or supranuclear ophthalmologic signs, psychiatric problems, and seizure disorders. The ataxia in ADCA Type I is characterized as disordered voluntary movement in (1) the rate of initiation and cessation called dyschronometria, (2) the amplitude known as dysmetria, (3) the coordination of single movements termed dyssynergia, (4) the speed of alternating movements called dysdiadochokinesia, and (5) the continuity resulting in action tremors [2]. Cerebellar ataxia can affect virtually any body part causing movement abnormalities. Gait, truncal, and limb ataxia are often the most evident cerebellar findings though nystagmus, saccadic abnormalities, and dysarthria are usually associated. Table 1 lists clini