Beta-propeller protein-associated neurodegeneration

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Beta-propeller protein-associated neurodegeneration (BPAN) is a disorder that damages the nervous system and is progressive, which means that it gradually gets worse. Affected individuals develop a buildup of iron in the brain that can be seen with medical imaging. For this reason, BPAN is classified as a type of disorder called neurodegeneration with brain iron accumulation (NBIA), although the iron accumulation may not occur until late in the disease.

Many people with BPAN have recurrent seizures (epilepsy) beginning in infancy or early childhood. Several different types of seizures can occur in this disorder, even in the same individual. Often the first type to occur are febrile seizures, which are triggered by a high fever. Affected individuals can also experience generalized tonic-clonic seizures (also known as grand mal seizures). This type of seizure affects the entire body, causing muscle rigidity, convulsions, and loss of consciousness. Other seizure types that can occur in this disorder include short lapses in awareness that can have the appearance of staring spells or daydreaming (absence seizures, also called petit mal seizures), sudden episodes of weak muscle tone (atonic seizures), involuntary muscle twitches (myoclonic seizures), or more pronounced movements called epileptic spasms. Some individuals have seizure patterns that resemble those in epileptic syndromes, such as West syndrome or Lennox-Gastaut syndrome.

Children with BPAN also have intellectual disability, delayed development including significant problems with vocabulary and producing speech (expressive language), and difficulty coordinating movements (ataxia). Ataxia can affect the ability to walk and perform fine motor skills such as using utensils. Affected individuals can have neurodevelopmental issues that are often compared to features of a disorder called Rett syndrome. These features include repeated hand wringing or clasping (stereotypic hand movements); teeth grinding (bruxism); sleep disturbances; and problems with communication and social interaction characteristic of autism spectrum disorder.

In late adolescence or early adulthood, individuals with BPAN may begin to experience a gradual loss of intellectual functioning (cognitive decline) that can lead to a severe loss of thinking and reasoning abilities (dementia). Worsening problems with movement also occur, including dystonia and parkinsonism. Dystonia is a condition characterized by involuntary, sustained muscle contractions. In BPAN, the dystonia often starts in the arms. Parkinsonism can include unusually slow movement (bradykinesia), rigidity, tremors, an inability to hold the body upright and balanced (postural instability), and a shuffling walk that can cause recurrent falls.

The lifespan of people with BPAN varies. With proper management of their signs and symptoms, affected individuals can live into middle age. Death may result from complications of dementia or movement problems, such as injuries from falls or swallowing difficulties (dysphagia) that can lead to a bacterial lung infection called aspiration pneumonia.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

BPAN is caused by variants (also called mutations) in the WDR45 gene. This gene provides instructions for making the WIPI4 protein. WIPI4 has a characteristic structure resembling a seven-bladed propeller, from which the name of the disorder is derived. The WIPI4 protein is involved in a process called autophagy, which helps clear unneeded materials from cells, including excess amounts of an iron storage protein called ferritin.

Most of the WDR45 gene variants identified in people with BPAN result in the absence of functioning WIPI4 protein. As a result, the process of autophagy is impaired, making cells less efficient at removing damaged cell structures and waste materials. Researchers suggest that nerve cells (neurons) may be particularly vulnerable to impaired autophagy because they have long extensions (axons and dendrites), making it even more difficult to transport the waste materials from these structures to the compartments in the cell body where recycling takes place (the lysosomes). The waste materials can build up in these areas and damage them. Damage to neurons results in the neurological problems that occur in BPAN.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition is inherited in an X-linked dominant pattern. The gene associated with this condition is located on the X chromosome, which is one of the two sex chromosomes. In females (who have two X chromosomes), a variant in one of the two copies of the gene in each cell is sufficient to cause the disorder. In males (who have only one X chromosome), a variant in the only copy of the gene in each cell causes the disorder. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.

In most X-linked dominant disorders, males experience more severe symptoms than females. While this is not always the case in BPAN, most individuals with the disorder are females, likely because a smaller number of affected males survive until birth.

Almost all cases of BPAN result from new variants in the gene and occur in people with no history of the disorder in their family. Rarely, an affected person inherits the variant from a mildly affected mother. Among reported cases, males with BPAN and most females with BPAN have not had children.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

BPAN is a rare disorder. Its prevalence is unknown, but it is thought to account for between 35 and 40 percent of all cases of NBIA disorders. Some individuals who have been diagnosed with intellectual disability or early-onset parkinsonism based on their signs and symptoms have later been found to have BPAN when genetic testing was done.

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 autonomic nervous system physiology · Frequent (79-30%)

A functional abnormality of the autonomic nervous system.

Abnormality of eye movement · Frequent (79-30%)

An abnormality in voluntary or involuntary eye movements or their control.

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).

Cerebellar atrophy · Frequent (79-30%)

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.

Cerebral atrophy · Frequent (79-30%)

Atrophy (wasting, decrease in size of cells or tissue) affecting the cerebrum.

Dementia · Frequent (79-30%)

A loss of global cognitive ability of sufficient amount to interfere with normal social or occupational function. Dementia represents a loss of previously present cognitive abilities, generally in adults, and can affect memory, thinking, language, judgment, and behavior.

Dystonia · Frequent (79-30%)

An abnormally increased muscular tone that causes fixed abnormal postures. There is a slow, intermittent twisting motion that leads to exaggerated turning and posture of the extremities and trunk.

Frontal release signs · Frequent (79-30%)

Primitive reflexes traditionally held to be a sign of disorders that affect the frontal lobes.

Other findings in the same source

From: Orphanet

Additional reported features include Global developmental delay (Frequent (79-30%)); Intellectual disability (Frequent (79-30%)); Iron accumulation in brain (Frequent (79-30%)); Iron accumulation in substantia nigra (Frequent (79-30%)); Parkinsonism (Frequent (79-30%)); Rigidity (Frequent (79-30%)); Sleep abnormality (Frequent (79-30%)); Spastic paraparesis (Frequent (79-30%)); Tremor (Frequent (79-30%)); Poor speech (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 Beta-propeller 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 Beta-propeller 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.