biology

Infantile neuroaxonal dystrophy

Infantile neuroaxonal dystrophy is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Infantile neuroaxonal dystrophy rather than just read about it. In short: Infantile neuroaxonal dystrophy (INAD) is a rare pervasive developmental 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.

Key takeaways

Infantile neuroaxonal dystrophy belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Infantile neuroaxonal dystrophy to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Infantile neuroaxonal dystrophy from memory before moving on to harder problems.

Reference excerpt

Infantile neuroaxonal dystrophy (INAD) is a rare pervasive developmental 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.

Presentation

Cause This condition is inherited in an autosomal recessive pattern, which means two copies of the gene (PLA2G6) in each cell are altered. Most often, the parents of an individual with an autosomal recessive disorder each carry one copy of the altered gene but do not show signs and symptoms of the disorder.

Pathophysiology Mutations in the PLA2G6 gene have been identified in most individuals with infantile neuroaxonal dystrophy. The PLA2G6 gene provides instructions for making an enzyme called an A2 phospholipase. This enzyme family is involved in metabolizing 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. This impairment of enzyme function 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 related disorder called pantothenate kinase-associated neurodegeneration. These disorders, as well as the more common Alzheimer disease and Parkinson 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 gene may be involved. Mutations in the NAGA gene, resulting in alpha-N-acetylgalactosaminidase deficiency, cause an infantile neuroaxonal dystrophy known as Schindler disease.

Diagnosis 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. Generally they 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 and 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 optic nerve are characteristic of infantile neuroaxonal dystrophy. Hearing loss may also develop. Children with this disorder experience progressive deterioration of cognitive functions (dementia), and 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. A part of the brain called the cerebellum, which helps to control movements, may also be damaged. In some individuals with infantile neuroaxonal dystrophy, abnormal amounts of iron accumulate in a specific region of the brain called the basal ganglia.

Management Currently, only palliative treatment is available: alleviation of spasticity and seizures, baclofen for relieving dystonia, physiotherapeutic treatment and measures such as gastric feeding tube or tracheostomy to prevent aspirational pneumonia.

Research An open-label clinical study for long-term evaluation of efficacy, safety, tolerability, and pharmacokinetics of a deuterium-enhanced polyunsaturated fatty acid RT001, which, when taken with food, can protect the neuronal cells from degeneration, started in the Summer 2018. The loss of iPLA2-VIA, the fly homolog of PLA2G6, reduces lifespan, impairs synaptic transmission, and causes neurodegeneration. Phospholipases typically hydrolyze glycerol phospholipids, but loss of iPLA2-VIA does not affect the phospholipid composition of brain tissue but rather causes an elevation in ceramides. Reducing ceramides with drugs, including myriocin or desipramine, alleviates lysosomal stress and suppresses neurodegeneration.

References

Further reading GeneReview/NIH/UW entry on Infantile Neuroaxonal Dystrophy National Library of Medicine. Genetics Home Reference - Infantile neuroaxonal dystrophy

External links

Illustrations

Worked examples

Example 1 — a first encounter with Infantile neuroaxonal dystrophy

Start with the simplest possible case. Write down what Infantile neuroaxonal dystrophy claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Infantile neuroaxonal dystrophy before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Infantile neuroaxonal dystrophy ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Infantile neuroaxonal dystrophy

In research: Infantile neuroaxonal dystrophy appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Infantile neuroaxonal dystrophy in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Infantile neuroaxonal dystrophy is common in secondary-school and first-year university syllabi. It links to neighbouring topics Autosomal recessive disorders, Neurodegeneration with brain iron accumulation, Pervasive developmental disorders, so understanding it makes those chapters shorter.
In everyday life: Look for Infantile neuroaxonal dystrophy outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Infantile neuroaxonal dystrophy in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Infantile neuroaxonal dystrophy means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Infantile neuroaxonal dystrophy out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Infantile neuroaxonal dystrophy in simple terms?

Why does Infantile neuroaxonal dystrophy matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Infantile neuroaxonal dystrophy?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Infantile neuroaxonal dystrophy.