Pyridoxal phosphate-responsive seizures

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Pyridoxal phosphate-responsive seizures (sometimes called pyridoxamine 5'-phosphate oxidase deficiency or PNPO deficiency) is a condition in which repeated seizures (epilepsy) typically begin within the first two weeks of life. In approximately 10 percent of individuals with PNPO deficiency, the seizures have a later onset, beginning after the first month of life. The seizures typically involve irregular involuntary muscle contractions (myoclonus), abnormal eye movements, or convulsions. In some cases, the seizures may last for several minutes or the seizures may occur too close together to allow for recovery between episodes (status epilepticus). Some babies with PNPO deficiency will experience seizures before birth, and some will experience a slow heart rate and a lack of oxygen before delivery (fetal distress).

Anticonvulsant medications, which are usually given to control seizures, are not effective in people with PNPO deficiency. Instead, individuals with PNPO deficiency require lifelong treatment with one of the following forms of vitamin B6: pyridoxal 5'-phosphate (PLP) or pyridoxine. If untreated, people with this condition can develop severe brain dysfunction (encephalopathy), which can lead to death. Even though seizures can be controlled with PLP or pyridoxine, people with PNPO deficiency may still experience neurological problems such as developmental delays, learning disorders, and uncontrolled movements (dystonia).

Other conditions present with signs and symptoms that are very similar to those seen in people with PNPO deficiency. These include pyridoxine-dependent epilepsy caused by changes in the ALDH7A1 gene and PLPBP deficiency caused by changes in the PLPBP gene. Individuals with these conditions are also typically treated with a form of vitamin B6.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Variants (also called mutations) in the PNPO gene cause PNPO deficiency. The PNPO gene provides instructions for producing an enzyme called pyridox(am)ine 5'-phosphate oxidase. This enzyme is involved in the breakdown (metabolism) of vitamin B6 into pyridoxal 5'-phosphate (PLP), the active form of vitamin B6. PLP is necessary for protein metabolism and the processing of chemicals that transmit signals in the brain (neurotransmitters).

Variants in the PNPO gene cause the gene to produce a version of the pyridox(am)ine 5'-phosphate oxidase enzyme that is unable to metabolize vitamin B6, leading to a deficiency of PLP. A shortage of PLP can disrupt the function of many other proteins and enzymes that need PLP in order to be effective. Because PLP plays an important role in neurotransmitter metabolism, a lack of PLP is believed to cause the seizures that are characteristic of PNPO deficiency.

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 must have a variant to cause the disorder. The parents of an individual with an autosomal recessive condition each carry one copy of the altered gene, but they typically do not show signs and symptoms of the condition.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

PNPO deficiency is a rare condition; as of 2022, approximately 90 individuals with PNPO deficiency have been described 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.

Epileptic encephalopathy · Very frequent (99-80%)

A condition in which epileptiform abnormalities are believed to contribute to the progressive disturbance in cerebral function. Epileptic encephalaopathy is characterized by (1) electrographic EEG paroxysmal activity that is often aggressive, (2) seizures that are usually multiform and intractable, (3) cognitive, behavioral and neurological deficits that may be relentless, and (4) sometimes early death.

Status epilepticus · Very frequent (99-80%)

Status epilepticus is a type of prolonged seizure resulting either from the failure of the mechanisms responsible for seizure termination or from the initiation of mechanisms which lead to abnormally prolonged seizures (after time point t1). It is a condition that can have long-term consequences (after time point t2), including neuronal death, neuronal injury, and alteration of neuronal networks, depending on the type and duration of seizures.

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

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

Abnormality of the amniotic fluid · Frequent (79-30%)

Abnormality of the amniotic fluid, which is the fluid contained in the amniotic sac surrounding the developing fetus.

Axial hypotonia · Frequent (79-30%)

Muscular hypotonia (abnormally low muscle tone) affecting the musculature of the trunk.

Decreased CSF homovanillic acid concentration · Frequent (79-30%)

Decreased concentration of homovanillic acid (HVA) in the cerebrospinal fluid. HVA is a metabolite of dopamine.

EEG with burst suppression · Frequent (79-30%)

The burst suppression pattern in electroencephalography refers to a characteristic periodic pattern of low voltage (<10 microvolts) suppressed background and a relatively shorter pattern of higher amplitude slow, sharp, and spiking complexes.

Failure to thrive · Frequent (79-30%)

Failure to thrive (FTT) refers to a child whose physical growth is substantially below the norm.

Other findings in the same source

From: Orphanet

Additional reported features include Feeding difficulties (Frequent (79-30%)); Global brain atrophy (Frequent (79-30%)); Global developmental delay (Frequent (79-30%)); High-pitched cry (Frequent (79-30%)); Hypertonia (Frequent (79-30%)); Hypoargininemia (Frequent (79-30%)); Hypoglycemia (Frequent (79-30%)); Increased circulating lactate concentration (Frequent (79-30%)); Metabolic acidosis (Frequent (79-30%)); Myoclonus (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 Pyridoxal phosphate-responsive seizures 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

Where the source describes treatments, these are an overview of possible care, not a prescription for an individual. Ask which option applies to the confirmed diagnosis, what benefit is expected, what adverse effects to watch for and how progress will be assessed. Availability, approvals and local practice can differ from the country described in the source.

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.