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IOSCA

Infantile-onset spinocerebellar ataxia

(often shortened to IOSCA)
Reviewed March 2010

What is IOSCA?

Infantile-onset spinocerebellar ataxia (IOSCA) is a progressive disorder that affects the nervous system. Babies with IOSCA develop normally during the first year of life. During early childhood, however, they begin experiencing difficulty coordinating movements (ataxia); very weak muscle tone (hypotonia); involuntary writhing movements of the limbs (athetosis); and decreased reflexes. By their teenage years affected individuals require wheelchair assistance.

People with IOSCA often develop problems with the autonomic nervous system, which controls involuntary body functions. As a result, they may experience excessive sweating, difficulty controlling urination, and severe constipation.

IOSCA also leads to vision and hearing problems that begin by about age 7. Children with this disorder develop weakness in the muscles that control eye movement (ophthalmoplegia). In their teenage years they experience degeneration of the nerves that carry information from the eyes to the brain (optic atrophy), which can result in vision loss. Hearing loss caused by nerve damage (sensorineural hearing loss) typically occurs during childhood and progresses to profound deafness.

Individuals with IOSCA may have recurrent seizures (epilepsy). These seizures can lead to severe brain dysfunction (encephalopathy).

Most people with IOSCA survive into adulthood. However, a few individuals with IOSCA have an especially severe form of the disorder involving liver damage and encephalopathy that develops during early childhood. These children do not generally live past age 5.

How common is IOSCA?

More than 20 individuals with IOSCA have been identified in Finland. A few individuals with similar symptoms have been reported elsewhere in Europe.

What genes are related to IOSCA?

Mutations in the C10orf2 gene cause IOSCA. The C10orf2 gene provides instructions for making two very similar proteins called Twinkle and Twinky. These proteins are found in the mitochondria, which are structures within cells that convert the energy from food into a form that cells can use.

Mitochondria each contain a small amount of DNA, known as mitochondrial DNA or mtDNA, which is essential for the normal function of these structures. The Twinkle protein is involved in the production and maintenance of mtDNA. The function of the Twinky protein is unknown.

The C10orf2 gene mutations that cause IOSCA interfere with the function of the Twinkle protein and result in reduced quantities of mtDNA (mtDNA depletion). Impaired mitochondrial function in the nervous system, muscles, and other tissues that require a large amount of energy leads to neurological dysfunction and the other problems associated with IOSCA.

Read more about the C10orf2 gene.

How do people inherit IOSCA?

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Where can I find information about diagnosis or management of IOSCA?

These resources address the diagnosis or management of IOSCA and may include treatment providers.

You might also find information on the diagnosis or management of IOSCA in Educational resources and Patient support.

General information about the diagnosis and management of genetic conditions is available in the Handbook. Read more about genetic testing, particularly the difference between clinical tests and research tests.

To locate a healthcare provider, see How can I find a genetics professional in my area? in the Handbook.

Where can I find additional information about IOSCA?

You may find the following resources about IOSCA helpful. These materials are written for the general public.

You may also be interested in these resources, which are designed for healthcare professionals and researchers.

What other names do people use for IOSCA?

  • Ohaha syndrome
  • ophthalmoplegia, hypotonia, ataxia, hypacusis, and athetosis

For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines and How are genetic conditions and genes named? in the Handbook.

What if I still have specific questions about IOSCA?

Where can I find general information about genetic conditions?

What glossary definitions help with understanding IOSCA?

References (6 links)

 

The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? in the Handbook.

 
Reviewed: March 2010
Published: November 24, 2014