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Disease Profile

Infantile onset spinocerebellar ataxia

Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.

<1 / 1 000 000

US Estimated

Europe Estimated

Age of onset






Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.


Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable


Other names (AKA)

Ophthalmoplegia, hypotonia, ataxia, hypacusis, and athetosis; OHAHA syndrome; IOSCA;


Congenital and Genetic Diseases; Digestive Diseases; Metabolic disorders;


The following summary is from Orphanet, a European reference portal for information on rare diseases and orphan drugs.

Orpha Number: 1186

Infantile-onset spinocerebellar ataxia (IOSCA) is a hereditary neurological disorder with early and severe involvement of both the peripheral and central nervous systems. It has only been described in Finnish families.

So far, 24 cases have been reported. In Finland, IOSCA has a population carrier frequency of more than 1:230.

Clinical description
IOSCA is characterized by very early ataxia, athetosis and reduced tendon reflexes (between 9 and 18 months of age). Ophthalmoplegia and sensorineural hearing loss are diagnosed in childhood. Other features, such as optic atrophy and sensory neuropathy with progressive loss of myelinated fibers in the sural nerve, appear later in the disease course. Hypogonadism may occur in females. Some patients show intellectual deficit. Epilepsy is a late manifestation and seizures may be life-threatening.

IOSCA is caused by mutations in the C10orf2 gene (10q24) encoding the mitochondrial helicase Twinkle. The c.1523A>G (p.Y508C) causative mutation has been postulated to be a founder mutation. Twenty-one of the reported patients were homozygous for this mutation, and three were compound heterozygotes: c.952G>A/c.1523A>G (two patients) and c.1523A>G/c.1287C>T (one patient). The mutations lead to mtDNA depletion in the brain and the liver, but not in the muscle.

Diagnostic methods
The diagnosis is based on clinical and pathological findings. Studies of sural nerve biopsies reveal an early and rapidly progressive axonal neuropathy. Neuroimaging studies revealing cerebellar atrophy and genetic testing for the c.1523A>G mutation may also help to confirm the diagnosis.

Differential diagnosis
Differential diagnoses include early-onset cerebellar ataxias with sensory axonal neuropathy and epileptic encephalopathy, mitochondrial disorders with axonal neuropathy (such as Friedreich ataxia), progressive external ophthalmoplegia (PEO), juvenileor adult-onset mitochondrial recessive ataxia syndrome (MIRAS), and POLG-related disorders (see theseterms).

Antenatal diagnosis
Prenatal testing may be available for families in which the disease-causing mutations have already been identified.

Genetic counseling
IOSCA is inherited in an autosomal recessive manner. Genetic counseling is an important clinical tool for preventing new cases, especially for couples with an affected first child: the risk of having an affected child in further pregnancies is 25%.

Management and treatment
IOSCA patients are often managed by a multidisciplinary team, involving a pediatrician, neurologist, psychiatrist, orthopedic surgeon, physical and occupational therapists, genetic counselor, and social worker. Treatment is symptomatic and may include: (1) hearing aids, speech therapy and sign language for deafness; (2) physical therapy, orthotic devices and orthopedic surgery for sensory axonal neuropathy; (3) walking aids, a wheelchair, physiotherapy and occupational therapy for ataxia; (4) antiepileptic drugs for seizures and (5) antipsychotics and antidepressants for psychiatric symptoms.

Prognosis is unfavorable. Patients are wheelchair-bound by adolescence. Early death is common due to severe seizures. The clinical course seems to be more rapid and severe (with death during infancy) in c.952G>A/ c.1523A>G compound heterozygotes.

Visit the Orphanet disease page for more resources.


This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

Medical Terms Other Names
Learn More:
80%-99% of people have these symptoms
Abnormality of the autonomic nervous system
Hearing impairment
Hearing defect

[ more ]

Eye muscle paralysis
Optic atrophy
Reduced tendon reflexes
5%-29% of people have these symptoms
Elevated hepatic transaminase
High liver enzymes
Percent of people who have these symptoms is not available through HPO
Absent tendon reflexes
Involuntary writhing movements in fingers, hands, toes, and feet
Atrophy/Degeneration affecting the brainstem
Autosomal recessive inheritance
Cerebellar atrophy
Degeneration of cerebellum
Cerebral cortical atrophy
Decrease in size of the outer layer of the brain due to loss of brain cells
Epilepsia partialis continua
Epileptic encephalopathy
Excessive daytime somnolence
Excessive daytime sleepiness
More than typical sleepiness during day

[ more ]

Generalized hypotonia
Decreased muscle tone
Low muscle tone

[ more ]

Hypergonadotropic hypogonadism
Intellectual disability
Mental deficiency
Mental retardation
Mental retardation, nonspecific

[ more ]

Loss of ability to walk
Intermittent migraine headaches
Migraine headache
Migraine headaches

[ more ]

Muscle weakness
Muscular weakness
Muscular hypotonia
Low or weak muscle tone
Involuntary, rapid, rhythmic eye movements
Poor eye contact
Worsens with time
Sensory axonal neuropathy
Specific learning disability
Status epilepticus
Repeated seizures without recovery between them


Making a diagnosis for a genetic or rare disease can often be challenging. Healthcare professionals typically look at a person’s medical history, symptoms, physical exam, and laboratory test results in order to make a diagnosis. The following resources provide information relating to diagnosis and testing for this condition. If you have questions about getting a diagnosis, you should contact a healthcare professional.

Testing Resources


    Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

    Organizations Supporting this Disease

      Learn more

      These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

      In-Depth Information

      • GeneReviews provides current, expert-authored, peer-reviewed, full-text articles describing the application of genetic testing to the diagnosis, management, and genetic counseling of patients with specific inherited conditions.
      • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
      • Online Mendelian Inheritance in Man (OMIM) is a catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
      • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
      • PubMed is a searchable database of medical literature and lists journal articles that discuss Infantile onset spinocerebellar ataxia. Click on the link to view a sample search on this topic.