SCA2 (ATXN2) Genetic Testing (Repeat Expansion)

Use

Spinocerebellar ataxias (SCAs) and episodic ataxias are the most common types of autosomal dominant cerebellar ataxias (ADCAs). SCAs are numbered based upon their time of identification. SCA3 is the most common type of SCA worldwide, followed by SCA2, SCA1, and SCA6. Some of the complicated forms have not been given a SCA number, like Dentatorubral Pallidoluysian Atrophy (DRPLA). Anticipation can be observed in the autosomal dominant ataxias in which CAG trinucleotide repeats occur. Anticipation results from expansion in the number of CAG repeats with transmission of the gene to subsequent generations. Most ADCAs have an overlap in clinical presentation, which makes it hard to differentiate. The most frequent clinical symptoms in all ADCAs are progressive adult-onset gait ataxia (often with hand dysmetria), and dysarthria associated with cerebellar atrophy. The episodic ataxias are characterized by periods of unsteady gait and often associated with nystagmus or dysarthria. Myokymia, vertigo, or hearing loss may occur in some of the subtypes. Permanent ataxia and even cerebellar atrophy may result late in the disease course. Repeat expansions in the ATXN2 gene may also be associated with Amyotrophic Lateral Sclerosis, or ALS. ALS is a neurodegenerative disease characterized by progressive motor neuron loss, muscle weakness and wasting, muscle spasticity, and loss of motor control.1 Several studies have shown that an intermediate allele length of 30-33 CAG repeats may correlate with an increased risk factor of ALS.2 ATXN2 reports include additional interpretation to cover ALS in addition to Spinocerebellar Ataxia type 2.