Early-onset cerebellar ataxia with retained tendon reflexes

Early-onset cerebellar ataxia with retained tendon reflexes (EOCA), also known as Harding ataxia or early-onset cerebellar ataxia type II, is a rare hereditary neurological disorder primarily affecting the cerebellum and its connections. Unlike Friedreich ataxia, which is the most common early-onset recessive ataxia and typically presents with absent tendon reflexes, EOCA is distinguished by the preservation or even exaggeration of deep tendon reflexes. The condition was delineated by Anita Harding in the 1980s as a clinically distinct entity among the early-onset cerebellar ataxias. The disease primarily affects the nervous system, particularly the cerebellum, which is responsible for coordination of movement and balance. Key clinical features include progressive cerebellar ataxia with onset typically before age 25, gait unsteadiness, limb incoordination, dysarthria (slurred speech), and nystagmus (involuntary eye movements). Importantly, deep tendon reflexes are preserved or brisk, which differentiates this condition from Friedreich ataxia. Some patients may also develop spasticity in the lower limbs, and mild sensory abnormalities may be present. The rate of progression is generally slower than Friedreich ataxia, and patients often maintain ambulation for longer periods. EOCA is now recognized as a genetically heterogeneous condition, meaning that mutations in several different genes can produce this clinical phenotype. There is no specific curative treatment currently available. Management is supportive and symptomatic, including physical therapy and occupational therapy to maintain mobility and function, speech therapy for dysarthria, and assistive devices as needed. Regular neurological follow-up is recommended to monitor disease progression and address emerging complications.

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