Infantile neuroaxonal dystrophy

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Infantile neuroaxonal dystrophy is a disorder that primarily affects the nervous system. Individuals with infantile neuroaxonal dystrophy typically do not have any symptoms at birth, but between the ages of about 6 and 18 months they begin to experience delays in acquiring new motor and intellectual skills, such as crawling or beginning to speak. Eventually they lose previously acquired skills (developmental regression). In some cases, signs and symptoms of infantile neuroaxonal dystrophy first appear later in childhood or during the teenage years and progress more slowly.

Children with infantile neuroaxonal dystrophy experience progressive difficulties with movement. They generally have muscles that are at first weak and "floppy" (hypotonic), and then gradually become very stiff (spastic). Eventually, affected children lose the ability to move independently. Lack of muscle strength causes difficulty with feeding. Muscle weakness can also result in breathing problems that can lead to frequent infections, such as pneumonia. Seizures occur in some affected children.

Rapid, involuntary eye movements (nystagmus), eyes that do not look in the same direction (strabismus), and vision loss due to deterioration (atrophy) of the nerve that carries information from the eye to the brain (the optic nerve) often occur in infantile neuroaxonal dystrophy. Hearing loss may also develop. Children with this disorder experience progressive deterioration of cognitive functions (dementia), and they eventually lose awareness of their surroundings.

Infantile neuroaxonal dystrophy is characterized by the development of swellings called spheroid bodies in the axons, the fibers that extend from nerve cells (neurons) and transmit impulses to muscles and other neurons. In some individuals with infantile neuroaxonal dystrophy, abnormal amounts of iron accumulate in a specific region of the brain called the basal ganglia. The relationship of these features to the symptoms of infantile neuroaxonal dystrophy is unknown.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Mutations in the PLA2G6 gene have been identified in most individuals with infantile neuroaxonal dystrophy. The PLA2G6 gene provides instructions for making a type of enzyme called an A2 phospholipase. This type of enzyme is involved in breaking down (metabolizing) fats called phospholipids. Phospholipid metabolism is important for many body processes, including helping to keep the cell membrane intact and functioning properly. Specifically, the A2 phospholipase produced from the PLA2G6 gene, sometimes called PLA2 group VI, helps to regulate the levels of a compound called phosphatidylcholine, which is abundant in the cell membrane.

Mutations in the PLA2G6 gene impair the function of the PLA2 group VI enzyme, which may disrupt cell membrane maintenance and contribute to the development of spheroid bodies in the nerve axons. Although it is unknown how changes in this enzyme's function lead to the signs and symptoms of infantile neuroaxonal dystrophy, phospholipid metabolism problems have been seen in both this disorder and a similar disorder called pantothenate kinase-associated neurodegeneration. These disorders, as well as the more common Alzheimer's disease and Parkinson's disease, also are associated with changes in brain iron metabolism. Researchers are studying the links between phospholipid defects, brain iron, and damage to nerve cells, but have not determined how the iron accumulation that occurs in some individuals with infantile neuroaxonal dystrophy may contribute to the features of this disorder.

A few individuals with infantile neuroaxonal dystrophy have not been found to have mutations in the PLA2G6 gene. The genetic cause of the condition in these cases is unknown; there is evidence that at least one other unidentified gene may be involved.

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

Infantile neuroaxonal dystrophy is a very rare disorder. Its specific incidence is unknown.

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.

Cerebellar atrophy · Very frequent (99-80%)

Cerebellar atrophy is defined as a cerebellum with initially normal structures, in a posterior fossa with normal size, which displays enlarged fissures (interfolial spaces) in comparison to the foliae secondary to loss of tissue. Cerebellar atrophy implies irreversible loss of tissue and result from an ongoing progressive disease until a final stage is reached or a single injury, e.g. an intoxication or infectious event.

Developmental regression · Very frequent (99-80%)

Loss of developmental skills, as manifested by loss of developmental milestones.

Psychomotor deterioration · Very frequent (99-80%)

Loss of previously present mental and motor abilities.

Abnormal cerebral white matter morphology · Frequent (79-30%)

An abnormality of the cerebral white matter.

Abnormal pyramidal sign · Frequent (79-30%)

Functional neurological abnormalities related to dysfunction of the pyramidal tract.

Abnormality of peripheral nerve conduction · Frequent (79-30%)

An abnormality of the conduction of electrical impulses by peripheral (motor or sensory) nerves. This finding is elicited by a nerve conduction study (NCS).

Abnormality of visual evoked potentials · Frequent (79-30%)

An anomaly of visually evoked potentials (VEP), which are electrical potentials, initiated by brief visual stimuli, which are recorded from the scalp overlying the visual cortex.

Ataxia · Frequent (79-30%)

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).

Other findings in the same source

From: Orphanet

Additional reported features include Axial hypotonia (Frequent (79-30%)); Cerebellar gliosis (Frequent (79-30%)); EMG: chronic denervation signs (Frequent (79-30%)); Eye of the tiger anomaly of globus pallidus (Frequent (79-30%)); Hyperreflexia (Frequent (79-30%)); Increased circulating lactate dehydrogenase concentration (Frequent (79-30%)); Iron accumulation in brain (Frequent (79-30%)); Mental deterioration (Frequent (79-30%)); Optic atrophy (Frequent (79-30%)); Peripheral axonal neuropathy (Frequent (79-30%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Infantile neuroaxonal dystrophy 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 neuroaxonal dystrophy. 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.