Ataxia with Oculomotor Apraxia Type 2

Alternate names

AOA2; SCAN 2; SCAR1; SCAN2; Autosomal recessive spinocerebellar ataxia-1; Ataxia-oculomotor apraxia type 2; Spinocerebellar ataxia with axonal neuropathy type 2

Definition

Ataxia with oculomotor apraxia type 2 (AOA2) is a rare condition that affects muscle control and coordination.

Cause

• Spinocerebellar ataxia with axonal neuropathy type 2 (SCAN2) is caused by changes (mutations) in the SETX gene, which provides instructions for making a protein that is involved in DNA repair.

Gene mutations

• People with a mutation in SETX make a reduced amount of this important protein.
• This leads to an accumulation of damaged DNA 'which can cause cells to become unstable and die'.
• Certain cells in the brain, such as those involved in coordinating movements (the cerebellum), appear to be most affected by cell death because these cells do not copy themselves to replace cells that have been lost.
• Scientists suspect that the loss of brain cells in the cerebellum causes the many signs and symptoms associated with SCAN2.

Inheritance

Autosomal recessive inheritance, a 25% chance

Spinocerebellar ataxia with axonal neuropathy type 2 is inherited in an autosomal recessive manner. This means that to be affected, a person must have a mutation in both copies of the responsible gene in each cell. Affected people inherit one mutated copy of the gene from each parent, who is referred to as a carrier. Carriers of an autosomal recessive condition typically do not have any signs or symptoms (they are unaffected). When 2 carriers of an autosomal recessive condition have children, each child has a:

• 25% (1 in 4) chance to be affected
• 50% (1 in 2) chance to be an unaffected carrier like each parent
• 25% chance to be unaffected and not be a carrier

Onset

The signs and symptoms of ataxia with oculomotor apraxia type 2 (AOA2) generally become apparent between age 7 and twenty five years.

Signs and symptoms

• Ataxia is often the first symptom and is a major cause of disability in the early stages of the condition.
• Most people with AOA2 also experience sensorimotor neuropathy which is associated with a decreased ability to move or feel (sensation) in certain parts of the body, especially the lower limbs.
• Other symptoms can include oculomotor apraxia, movement disorders, and mild cognitive impairment.

Clinical presentation

For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. 80%-99% of people have these symptoms

• Areflexia(Absent tendon reflexes)
• Ataxia
• Cerebellar vermis atrophy
• Sensorimotor neuropathy(Nerve damage causing decreased feeling and movement)

30%-79% of people have these symptoms

• Elevated alpha-fetoprotein
• Gait imbalance(Abnormality of balance)
• Gaze-evoked nystagmus
• Oculomotor apraxia
• Saccadic smooth pursuit
• Sensory impairment

5%-29% of people have these symptoms

• Babinski sign
• Choreoathetosis
• Conjunctival telangiectasia(Small dilated blood vessels near membrane covering front of eye and eyelids)
• Dysphagia(Poor swallowing)
• Dystonia
• Elevated serum creatine kinase(Elevated blood creatine phosphokinase)
• Head tremor
• Hypercholesterolemia(Elevated serum cholesterol)
• Hypoalbuminemia(Low blood albumin)
• Postural tremor
• Strabismus(Squint eyes)
• Urinary bladder sphincter dysfunction

1%-4% of people have these symptoms

• Cerebellar atrophy(Degeneration of cerebellum)
• Chorea
• Distal amyotrophy(Distal muscle wasting)
• Distal muscle weakness(Weakness of outermost muscles)
• Dysarthria(Difficulty articulating speech)
• Gait ataxia(Inability to coordinate movements when walking)
• Hyporeflexia(Decreased reflex response)
• Impaired distal tactile sensation(Decreased touch sensation in extremities)
• Impaired proprioception
• Nystagmus(Involuntary, rapid, rhythmic eye movements)
• Peripheral axonal neuropathy
• Pes cavus(High-arched foot)
• Scoliosis
• Tremor

Diagnosis

A diagnosis of spinocerebellar ataxia with axonal neuropathy type 2 is often suspected based on the presence of characteristic signs and symptoms. Additional testing may then be ordered to confirm the diagnosis and to rule out other conditions that are associated with similar features. This testing may include:

• Imaging studies, such as magnetic resonance imaging (MRI)
• Electromyography
• Special blood tests
• Nerve biopsy
• Genetic testing

Treatment

• Although there is no cure for spinocerebellar ataxia with axonal neuropathy type 2 (SCAN2), treatments are available to help manage the signs and symptoms of the condition.
• For example, affected people may benefit from physical therapy and speech therapy.
• A wheelchair or other devices may be necessary to help maintain mobility.
• Children with SCAN2 may also need additional help in school since they may have difficulties with reading, writing and other activities.
• In some cases, a low-cholesterol diet may be recommended.

NIH genetic and rare disease info

• NIH info on Ataxia with Oculomotor Apraxia Type 2

Ataxia with Oculomotor Apraxia Type 2 is a rare disease.

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