Spinocerebellar ataxia type 1

Spinocerebellar ataxia type 1
Other names	SCA1, Schut's disease
AXH domain of Ataxin 1
Specialty	Neurology
Symptoms	Ataxia of gait and stance, hypermetric saccades, dysarthria, dysphagia
Complications	Pneumonia, physical injury from falls
Usual onset	Between 3rd and 4th decade
Duration	Long term
Causes	Genetic
Diagnostic method	Genetic testing
Prognosis	10–30 years from onset
Frequency	1–2 per 100,000

Spinocerebellar ataxia type 1 (SCA1) is a rare autosomal dominant disorder, which, like other spinocerebellar ataxias, is characterized by neurological symptoms including dysarthria, hypermetric saccades, and ataxia of gait and stance. This cerebellar dysfunction is progressive and permanent. First onset of symptoms is normally between 30 and 40 years of age, though juvenile onset can occur. Death typically occurs within 10 to 30 years from onset.

SCA1 is typically inherited from the parents in an autosomal dominant regime; the children of a person with the disease have a 50% chance of inheriting it themselves, and new mutations can occur in some cases. It is caused by an expanded number of trinucleotide repeats in the polyglutamine tract of the ATXN1 gene, which encodes the ataxin 1 protein. This expansion results in a larger than normal number of repeats of the nucleotide sequence cytosine, adenine, guanine, or CAG, in the gene which, in turn, results in a larger than normal number of consecutive glutamine amino acid residues in the protein. This mutant protein causes degradation in certain types of neurons, like Purkinje neurons, which are common in the cerebellum, spinal cord, and related parts of the brain. While the mechanism is not fully understood, it is suspected that changes in the interactions between ataxin 1 and other proteins result in a toxic gain of function.

The mutation can be detected before or after the onset of symptoms by genetic testing. Currently, no cure for SCA1 is known, so treatment of the disease focuses primarily on management of symptoms to maintain quality of life, focusing on physical therapy to retrain and replace lost functions. Research to develop treatments is ongoing and in addition to conventional pharmaceutical treatment, SCA1 has been the subject of research into more advanced treatment options such as gene therapy and stem cell therapy. Worldwide, an expected 1 to 2 people in 100,000 have spinocerebellar ataxia type 1, however, the prevalence varies between populations and is often linked to the founders effect.

Ataxia as a symptom has been known since the mid 19th century and the heterogeneous group of diseases now known as spinocerebellar ataxias was the subject of extensive research in the latter part of that century. Advances in molecular genetics in the 20th century allowed distinct causes of these diseases to be identified. In the early 1990s the gene causing SCA1 was localized to the human leukocyte antigen complex on chromosome 6 and by 1993, ataxin 1 was identified as the causative gene. It was the first spinocerebellar ataxia-causing gene to be localized and identified.