Mitochondrial membrane protein-associated neurodegeneration

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Mitochondrial membrane protein-associated neurodegeneration (MPAN) is a disorder of the nervous system. The condition typically begins in childhood or early adulthood and worsens (progresses) over time.

MPAN commonly begins with difficulty walking. As the condition progresses, affected individuals usually develop other movement problems, including muscle stiffness (spasticity) and involuntary muscle cramping (dystonia). Many people with MPAN have a pattern of movement abnormalities known as parkinsonism. These abnormalities include unusually slow movement (bradykinesia), muscle rigidity, involuntary trembling (tremors), and an inability to hold the body upright and balanced (postural instability).

Other neurological problems that occur in individuals with MPAN include degeneration of the nerve cells that carry visual information from the eyes to the brain (optic atrophy), which can impair vision; problems with speech (dysarthria); difficulty swallowing (dysphagia); and, in later stages of the condition, an inability to control the bowels or the flow of urine (incontinence). Additionally, affected individuals may experience a loss of intellectual function (dementia) and psychiatric symptoms such as behavioral problems, mood swings, hyperactivity, and depression.

MPAN is characterized by an abnormal buildup of iron in certain regions of the brain. Because of these deposits, MPAN is considered part of a group of conditions known as neurodegeneration with brain iron accumulation (NBIA).

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Mutations in the C19orf12 gene cause MPAN. The protein produced from this gene is found in the membrane of cellular structures called mitochondria, which are the energy-producing centers of the cell. Although its function is unknown, researchers suggest that the C19orf12 protein plays a role in the maintenance of fat (lipid) molecules, a process known as lipid homeostasis.

The gene mutations that cause this condition lead to an altered C19orf12 protein that likely has little or no function. It is unclear how these genetic changes lead to the neurological problems associated with MPAN. Researchers are working to determine whether there is a link between problems with lipid homeostasis and brain iron accumulation and how these abnormalities might contribute to the features of this disorder.

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

MPAN is a rare condition that is estimated to affect less than 1 in 1 million people.

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.

Atypical behavior · Very frequent (99-80%)

Atypical behavior is an abnormality in a person's actions that can be controlled or modulated by the will of the individual. While abnormal behaviors can be difficult to control, they are distinct from other abnormal actions that cannot be affected by the individual's will.

Babinski sign · Very frequent (99-80%)

Upturning of the big toe (and sometimes fanning of the other toes) in response to stimulation of the sole of the foot. If the Babinski sign is present it can indicate damage to the corticospinal tract.

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.

Hand tremor · Very frequent (99-80%)

An unintentional, oscillating to-and-fro muscle movement affecting the hand.

Mental deterioration · Very frequent (99-80%)

Loss of previously present mental abilities, generally in adults.

Muscle weakness · Very frequent (99-80%)

Reduced strength of muscles.

Postural instability · Very frequent (99-80%)

A tendency to fall or the inability to keep oneself from falling; imbalance. The retropulsion test is widely regarded as the gold standard to evaluate postural instability, Use of the retropulsion test includes a rapid balance perturbation in the backward direction, and the number of balance correcting steps (or total absence thereof) is used to rate the degree of postural instability. Healthy subjects correct such perturbations with either one or two large steps, or without taking any steps, hinging rapidly at the hips while swinging the arms forward as a counterweight. In patients with balance impairment, balance correcting steps are often too small, forcing patients to take more than two steps. Taking three or more steps is generally considered to be abnormal, and taking more than five steps is regarded as being clearly abnormal. Markedly affected patients continue to step backward without ever regaining their balance and must be caught by the examiner (this would be called true retropulsion). Even more severely affected patients fail to correct entirely, and fall backward like a pushed toy soldier, without taking any corrective steps.

Rigidity · Very frequent (99-80%)

Continuous involuntary sustained muscle contraction. When an affected muscle is passively stretched, the degree of resistance remains constant regardless of the rate at which the muscle is stretched. This feature helps to distinguish rigidity from muscle spasticity.

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.

Abnormal globus pallidus morphology · Frequent (79-30%)

An abnormality of the globus pallidus.

Abnormality of the substantia nigra · Frequent (79-30%)

A structural anomaly of the substantia nigra, which is a midbrain dopaminergic nucleus which has a critical role in modulating motor movement and reward functions as part of the basal ganglia circuitry.

Bowel incontinence · Frequent (79-30%)

Involuntary fecal soiling in adults and children who have usually already been toilet trained.

Bradykinesia · Frequent (79-30%)

Bradykinesia literally means slow movement, and is used clinically to denote a slowness in the execution of movement (in contrast to hypokinesia, which is used to refer to slowness in the initiation of movement).

Dysphagia · Frequent (79-30%)

Difficulty in swallowing.

Other findings in the same source

From: Orphanet

Additional reported features include Dystonia (Frequent (79-30%)); Gait disturbance (Frequent (79-30%)); Motor axonal neuropathy (Frequent (79-30%)); Optic atrophy (Frequent (79-30%)); Parkinsonism (Frequent (79-30%)); Spastic paraparesis (Frequent (79-30%)); Urinary incontinence (Frequent (79-30%)); Frequent falls (Frequent (79-30%)); Hyperactive deep tendon reflexes (Frequent (79-30%)); Abnormal saccadic eye movements (Occasional (29-5%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Mitochondrial membrane protein-associated neurodegeneration 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 Mitochondrial membrane protein-associated neurodegeneration. 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.