Spinocerebellar ataxia type 2 -SCA2- (Spinocerebellar ataxia type 2 -SCA2-) - Gen ATXN2

Type 2 spinocerebellar ataxia (SCA2: Spinocerebellar Ataxia type 2), it is a process characterized by progressive movement problems affecting motor and balance (ataxia) coordination. Other signs include impairment of speech and swallowing, spasticity and weakness of ocular motor muscles (ophthalmoplegia). The weakness of the eye muscles, causing rapid involuntary eye movements (nystagmus). Patients may have difficulty processing, learn and remember information (cognitive impairment). SCA2 is characterized by cerebellar ataxia, neurologically impaired, accompanied by macular degeneration and retinal. Eventually, individuals with SCA2 may develop peripheral neuropathy, loss of muscle mass (atrophy), dystonia and chorea. Individuals with SCA2 may have problems with short term memory, planning and problem solving, or have dementia. Signs and symptoms of SCA2 usually begin in mid-adulthood, but can occur at any time from childhood to late adulthood. People with SCA2 generally survive 10 to 20 years after the onset of symptoms.

The mutations in the affected ATXN2 gene, located on the long arm of chromosome 12 (12q24.1). This gene contains the information for the synthesis of the "ataxin-2" protein. This protein is found in the cell cytoplasm, where would interact with the endoplasmic reticulum, which is involved in the synthesis, processing and intracellular transport of proteins.

ATXN2 gene mutations affect a part of the DNA sequence of chromosome 12 CAG repeats, located at the 5'end of the gene. Typically, the sequence CAG repeats has 22 repetitions, and even individuals can have up to 31 repetitions without any alteration triggered. In those affected by SCA2, this triplet is repeated 32 or more times. When there are 32 or 33 repetitions, the first signs and symptoms appear late in adults; whereas when there are 45 repeats the signs and symptoms develop in adolescence. The increase in length of the sequence CAG repeats, resulting in a protein "ataxin-2" anomalous leading to cell death, loss of brain cells in various brain areas. As it evolves, the cell loss in the brain leads to the characteristic movement problems SCA2.

The disease has an autosomal dominant, which means that a single copy of the gene altered in each cell is sufficient to trigger the disease. An affected person inherits the altered gene from one affected parent, although some affected do not have a parent with the disease. When moving from one generation to the next, the length of the sequence CAG triplet repeat usually increases, and repeats often associated with earlier onset of signs and symptoms (anticipation). which in turn it is more evident when the altered gene is inherited from the father. Anticipation tends to be more prominent when the ATXN2 altered gene is inherited from the father (paternal inheritance) than when inherited from the mother (maternal inheritance).

Tests in IVAMI: in IVAMI perform detection of mutations associated conataxia spinocerebellar type 2 (SCA2), by complete PCR amplification of exons ATXN2 gene, and subsequent sequencing.

Samples recommended: EDTA blood collected for separation of blood leukocytes, or impregnated sample card with dried blood (IVAMI may mail the card to deposit the blood sample).