Infantile-onset ascending hereditary spastic paralysis

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Infantile-onset ascending hereditary spastic paralysis is one of a group of genetic disorders known as hereditary spastic paraplegias. These disorders are characterized by progressive muscle stiffness (spasticity) and eventual paralysis of the lower limbs (paraplegia). The spasticity and paraplegia result from degeneration (atrophy) of motor neurons, which are specialized nerve cells in the brain and spinal cord that control muscle movement. Hereditary spastic paraplegias are divided into two types: pure and complicated. The pure types involve only the lower limbs, while the complicated types involve additional areas of the nervous system, affecting the upper limbs and other areas of the body. Infantile-onset ascending hereditary spastic paralysis starts as a pure hereditary spastic paraplegia, with spasticity and weakness in the legs only, but as the disorder progresses, the muscles in the arms, neck, and head become involved and features of the disorder are more characteristic of the complicated type.

Affected infants are typically normal at birth, then within the first 2 years of life, the initial symptoms of infantile-onset ascending hereditary spastic paralysis appear. Early symptoms include exaggerated reflexes (hyperreflexia) and recurrent muscle spasms in the legs. As the condition progresses, affected children develop abnormal tightness and stiffness in the leg muscles and weakness in the legs and arms. Over time, muscle weakness and stiffness travels up (ascends) the body from the legs to the head and neck. Muscles in the head and neck usually weaken during adolescence; symptoms include slow eye movements and difficulty with speech and swallowing. Affected individuals may lose the ability to speak (anarthria). The leg and arm muscle weakness can become so severe as to lead to paralysis; as a result affected individuals require wheelchair assistance by late childhood or early adolescence. Intelligence is not affected in this condition.

A condition called juvenile primary lateral sclerosis shares many of the features of infantile-onset ascending hereditary spastic paralysis. Both conditions have the same genetic cause and significantly impair movement beginning in childhood; however, the pattern of nerve degeneration is different. Because of their similarities, these conditions are sometimes considered the same disorder.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Infantile-onset ascending hereditary spastic paralysis is caused by mutations in the ALS2 gene. This gene provides instructions for making the alsin protein. Alsin is produced in a wide range of tissues, with highest amounts in the brain, particularly in motor neurons. Alsin turns on (activates) multiple proteins called GTPases that convert a molecule called GTP into another molecule called GDP. GTPases play important roles in several cell processes. The GTPases that are activated by alsin are involved in the proper placement of the various proteins and fats that make up the cell membrane, the transport of molecules from the cell membrane to the interior of the cell (endocytosis), and the development of specialized structures called axons and dendrites that project from neurons and are essential for the transmission of nerve impulses.

Mutations in the ALS2 gene alter the instructions for making alsin, often resulting in the production of an abnormally short alsin protein that is unstable and rapidly broken down. It is unclear exactly how ALS2 gene mutations cause infantile-onset ascending hereditary spastic paralysis. Research suggests that a lack of alsin and the subsequent loss of GTPase functions, such as endocytosis and the development of axons and dendrites, contribute to the progressive atrophy of motor neurons that is characteristic of this condition.

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-onset ascending hereditary spastic paralysis is a rare disorder, with at least 30 cases reported in the scientific literature.

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.

Abnormal pyramidal sign · Very frequent (99-80%)

Functional neurological abnormalities related to dysfunction of the pyramidal tract.

Anarthria · Very frequent (99-80%)

A defect in the motor ability that enables speech.

Dysarthria · Very frequent (99-80%)

Dysarthric speech is a general description referring to a neurological speech disorder characterized by poor articulation. Depending on the involved neurological structures, dysarthria may be further classified as spastic, flaccid, ataxic, hyperkinetic and hypokinetic, or mixed.

Hyperreflexia · Very frequent (99-80%)

Hyperreflexia is the presence of hyperactive stretch reflexes of the muscles.

Impaired mastication · Very frequent (99-80%)

An abnormal reduction in the ability to masticate (chew), i.e., in the ability to crush and ground food in preparation for swallowing.

Spastic paraplegia · Very frequent (99-80%)

Complete loss of the ability to move the lower limbs accompanied by spasticity of the lower limbs.

Spastic tetraplegia · Very frequent (99-80%)

Spastic paralysis affecting all four limbs.

Spasticity · Very frequent (99-80%)

A motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes with increased muscle tone, exaggerated (hyperexcitable) tendon reflexes.

Other findings in the same source

From: Orphanet

Additional reported features include Tetraplegia (Very frequent (99-80%)); Abnormality of eye movement (Frequent (79-30%)); Pseudobulbar behavioral symptoms (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-onset ascending hereditary spastic paralysis 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 ascending hereditary spastic paralysis. 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.