SNP Shot: Genomic Insights

Spinocerebellar ataxia type 36 (SCA36) is a progressive movement disorder that typically appears in mid-adulthood. Individuals with SCA36 initially experience ataxia, which is characterized by impaired coordination and balance. Other early signs often include hyperreflexia (exaggerated reflexes) and dysarthria (speech difficulties). A common symptom is fasciculations (muscle twitches) of the tongue, which eventually lead to tongue atrophy (muscle wasting). These tongue problems can cause difficulty swallowing liquids. As the disease progresses, muscle atrophy develops in the legs, forearms, and hands. Furthermore, SCA36 often involves the atrophy of motor neurons, which are nerve cells crucial for muscle control. This motor neuron loss contributes to muscle atrophy in the tongue and limbs.

Eye muscle abnormalities are observed in some SCA36 patients, potentially causing nystagmus (involuntary eye movements), saccades (rapid eye movements), oculomotor apraxia (difficulty moving the eyes side to side), and ptosis (drooping eyelids). Sensorineural hearing loss, resulting from inner ear changes, can also occur.

Brain scans of individuals with SCA36 reveal progressive brain atrophy, particularly in the cerebellum, the region responsible for coordinating movements. The loss of cerebellar cells leads to the characteristic movement problems of SCA36. In some older individuals, atrophy of the frontal lobes may be observed, resulting in a decline in executive function, which encompasses the ability to plan, implement actions, and solve problems.

The onset of SCA36 symptoms typically occurs in a person's forties or fifties, although it can manifest at any point during adulthood. Individuals with SCA36 generally have a normal lifespan and remain mobile for approximately 15 to 20 years following diagnosis.

Inheritance:

SCA36 follows an autosomal dominant inheritance pattern. This means that only one copy of the mutated gene in each cell is enough to cause the disorder. In most instances, an affected individual has one parent who also has the condition. In conditions caused by repeated DNA segments, the number of repeats can increase as the gene is passed to subsequent generations. A larger number of repeats is often correlated with an earlier onset of symptoms, a phenomenon known as anticipation. Anticipation has been observed in some, but not all, SCA36 families. When present, anticipation is most frequently observed when the mutated gene is inherited from the affected father.