Pelizaeus-Merzbacher-like disease type 1

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Pelizaeus-Merzbacher-like disease type 1 is an inherited condition involving the brain and spinal cord (central nervous system). This disease is one of a group of genetic disorders called leukodystrophies. Leukodystrophies are abnormalities of the nervous system's white matter, which consists of nerve fibers covered by a fatty substance called myelin. Myelin insulates nerve fibers and promotes the rapid transmission of nerve impulses. In particular, Pelizaeus-Merzbacher-like disease type 1 involves hypomyelination, which means that the nervous system has a reduced ability to form myelin. The signs and symptoms of this condition are very similar to another leukodystrophy called Pelizaeus-Merzbacher disease, but the two disorders have different genetic causes.

Beginning in the first few months of life, infants with Pelizaeus-Merzbacher-like disease type 1 typically experience weak muscle tone (hypotonia), involuntary movements of the eyes (nystagmus), and delayed development of speech and motor skills, such as sitting or grasping objects. As children with Pelizaeus-Merzbacher-like disease type 1 get older, hypotonia changes to muscle stiffness (spasticity).

During childhood, individuals with Pelizaeus-Merzbacher-like disease type 1 develop problems with movement and balance (ataxia), difficulty with movements that involve judging distance or scale (dysmetria), tremors that occur mainly during movement (intention tremors), and head and neck tremors (titubation). People with this condition have an inability to perform quick, alternating movements (dysdiadochokinesia), such as quickly tapping different fingers. Some develop involuntary tensing of the muscles (dystonia) and jerking (choreiform) movements. Many people with Pelizaeus-Merzbacher-like disease type 1 develop skeletal issues such as an abnormal curvature of the spine (scoliosis) and require wheelchair assistance from childhood.

Muscle abnormalities can lead to difficulty swallowing and problems producing speech (expressive language), but affected individuals can understand speech (receptive language). Most individuals with Pelizaeus-Merzbacher-like disease type 1 have normal intelligence. Rarely, hearing loss, optic atrophy, and recurrent seizures (epilepsy) can occur.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Pelizaeus-Merzbacher-like disease type 1 is caused by mutations in the GJC2 gene. This gene provides instructions for making a protein called connexin-47. This protein plays a role in forming channels called gap junctions between cells. Gap junctions made with connexin-47 facilitate communication between nervous system cells called oligodendrocytes or between oligodendrocytes and another type of nervous system cell called astrocytes. Communication between these cells is necessary for the formation of myelin.

GJC2 gene mutations that cause Pelizaeus-Merzbacher-like disease type 1 reduce the production of connexin-47, prevent the connexin-47 protein from reaching the cell membrane, or decrease the function of the protein in the gap junction. All of these GJC2 gene mutations disrupt the communication between nerve cells that normally occurs at gap junctions and impair myelin formation. These changes lead to nerve damage in the brain and spinal cord that impairs nervous system function, resulting in the signs and symptoms of Pelizaeus-Merzbacher-like disease type 1.

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

The prevalence of Pelizaeus-Merzbacher-like disease type 1 is unknown, but it is thought to be rare.

Which doctor should you see?

The suggested department for discussing Pelizaeus-Merzbacher-like disease type 1 is Clinical Genetics, with a clinical geneticist as the relevant type of clinician. Paediatrician (children) or physician (adults), with clinical geneticist referral.

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.

• Does the exact genetic or chromosome finding explain the observed features?
• Would a genetic counsellor help the family understand the result?
• Which organ-specific assessments are appropriate for this particular diagnosis?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Pelizaeus-Merzbacher-like disease type 1. 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.