Spinocerebellar Ataxia 18

Background and History: 

In view of the amount of complexity in the brain, it is not surprising that many gene mutations negatively impact its function.  When these alter the structure and development of a substructure known as the cerebellum, symptoms of unsteadiness, eye movement disorders, and slurred speech can occur as in the condition described here. 

Clinical Correlations: 

There are no external deformities and children at birth can appear normal.  However, within a year developmental delays are evident in activities such as sitting alone.  Later, evidence of intellectual disability becomes evident although this is variable in severity.  Speech may also be delayed and is never normal with even some older children only speaking single words or abbreviated sentences.  Some slurring of words is common.  Walking is never normal and requires some assistance from the beginning.  Contractions of joints can lead to further difficulties in ambulation and by the second decade some individuals are confined to a wheelchair.

Eye movements are often abnormal.  Some individuals have constant to-and-fro movements while others a have rotatory component (nystagmus).  Still others have an intermittent or nearly constant upward gaze while still others have difficulty tracking moving targets, instead using head turns or jerky movements of the eyes.  The optic nerve that connects the eye to the brain is often damaged (optic atrophy) but the level of vision has not been measured.

The intellectual level of function does not seem to worsen.  However, MRI imaging of the brain shows progressive damage in the cerebellum.


A double dose of a gene mutation is responsible for this condition.  Both parents, who each carry one copy of the mutation, are clinically normal but each of their children has a 25% chance of inheriting this disorder.  The pattern of transmission is autosomal recessive.

Diagnosis and Prognosis: 

The diagnosis can be made at several months of age.  Pediatric neurologists and ophthalmologists most likely collaborate in making the diagnosis but because of similarities in signs to other forms of ataxia a test for the gene mutation may be required for certainty.

There is no treatment known for this condition.  However, appropriate braces and other assistive devices for mobility, low vision aids, and physical therapy might be helpful.  Little is known about the prognosis.

Additional Information
Autosomal recessive