Infantile-onset spinocerebellar ataxia

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

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.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Mutations in the TWNK gene cause IOSCA. The TWNK 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 TWNK 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.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

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.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

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

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Abnormality of movement · Very frequent (99-80%)

An abnormality of movement with a neurological basis characterized by changes in coordination and speed of voluntary movements.

Abnormality of the autonomic nervous system · Very frequent (99-80%)

An abnormality of the autonomic nervous system.

Ataxia · Very frequent (99-80%)

Ataxia refers to impaired coordination of voluntary muscle movement. Cerebellar ataxia refers to ataxia due to dysfunction of the cerebellum. This causes a variety of elementary neurological deficits including asynergy (lack of coordination between muscles, limbs and joints), dysmetria (lack of ability to judge distances that can lead to under- or overshoot in grasping movements), and dysdiadochokinesia (inability to perform rapid movements requiring antagonizing muscle groups to be switched on and off repeatedly).

Hearing impairment · Very frequent (99-80%)

A decreased magnitude of the sensory perception of sound.

Ophthalmoplegia · Very frequent (99-80%)

Paralysis of one or more extraocular muscles that are responsible for eye movements.

Optic atrophy · Very frequent (99-80%)

Atrophy of the optic nerve. Optic atrophy results from the death of the retinal ganglion cell axons that comprise the optic nerve and manifesting as a pale optic nerve on fundoscopy.

Reduced tendon reflexes · Very frequent (99-80%)

A reduction (hyporeflexia) or complete absence (areflexia) of the involuntary muscle contraction normally elicited by a reflex stimulus, such as tapping a deep tendon.

Which doctor should you see?

The suggested department for discussing Infantile-onset spinocerebellar ataxia is Neurology, with a neurologist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Which nervous-system findings help explain the symptoms?
• Would an assessment of walking, communication or daily function be helpful?
• Are rehabilitation or other specialist services relevant?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Infantile-onset spinocerebellar ataxia. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.