India has a diverse population with considerable genetic variation between regions and communities. Several hereditary ataxias have been reported in Indian patients, including spinocerebellar ataxia type 12 (SCA12), spinocerebellar ataxia type 2 (SCA2), SCA1, SCA3 and Friedreich ataxia. The relative frequency of these conditions varies across studies and populations, so one type cannot be assumed to be the most common throughout the entire country.

SCA12 is an important hereditary ataxia reported in India, particularly in certain families from northern India. It is associated with a CAG repeat expansion in the PPP2R2B gene. Symptoms can include progressive tremor, difficulty with balance, impaired coordination and changes in walking. The age at onset and severity can differ considerably between affected individuals.

SCA2 is another frequently identified type. It results from a CAG repeat expansion in the ATXN2 gene. People may experience progressive gait instability, limb incoordination, slowed eye movements and, in some cases, other neurological features. SCA2 is inherited in an autosomal dominant pattern, meaning that an affected individual with a disease-causing variant generally has a 50% chance of passing it to each child.

SCA1 and SCA3 are also important causes of inherited cerebellar degeneration. Friedreich ataxia differs from the common dominant SCAs because it is generally inherited in an autosomal recessive pattern and is associated with pathogenic variants affecting the FXN gene. It may involve the heart, sensory nerves and other systems in addition to coordination difficulties.

The most frequently diagnosed type depends on the geographical area, family history, clinical referral patterns and the genetic tests used. Some studies have focused on particular communities or specialist centres and therefore may not represent the entire Indian population.

Diagnosis requires appropriate genetic testing. Repeat-expansion disorders such as SCA1, SCA2, SCA3 and SCA12 often require dedicated repeat-expansion testing because routine exome sequencing may not reliably identify the relevant expansions.