Resources for healthcare professionals
Clinical information, diagnostic resources, research updates, and specialist support for healthcare professionals involved in the care of individuals affected by PMD and PMLD.
PMD Clinical overview
Pelizaeus-Merzbacher disease (PMD) is a rare X-linked hypomyelinating leukodystrophy caused by pathogenic variants in the PLP1 gene. Disease severity exists along a clinical spectrum, ranging from severe early-onset disease (PMD) to comparatively mild hereditary spastic paraplegia (SPG2) phenotypes.
Clinical manifestations result from abnormalities in central nervous system myelin development and maintenance, leading to varying degrees of motor impairment, developmental delay, spasticity, ataxia, and other neurological complications.
Historically, PLP1-related disorders have been classified into several phenotypes based on age of onset, symptom severity, and disease progression.
Connatal PMD represents the most severe form of the disease and typically presents during infancy.
Affected children often demonstrate:
- Severe hypotonia
- Stridor or respiratory difficulties
- Feeding difficulties
- Congenital or early-onset nystagmus
- Profound motor impairment
- Significant developmental delay
Motor milestones are often severely limited or absent, and many individuals require substantial medical and supportive care throughout life.
Classic PMD is the most commonly recognized phenotype and usually presents during infancy or early childhood.
Common features include:
- Nystagmus within the first months of life
- Delayed motor development
- Hypotonia evolving into spasticity
- Ataxia
- Dysarthria
- Variable cognitive impairment
Disease progression is typically slower than in connatal PMD, and many individuals survive into adolescence and adulthood.
Complicated SPG2 and HEMS are more recently recognized PLP1-related phenotypes associated with specific pathogenic variants affecting PLP1 protein function. They are generally considered less severe than classic PMD but presentation remains highly variable between individuals.
Clinical features may include:
- Early developmental delay
- Nystagmus
- Ataxia
- Spastic gait
- Autonomic dysfunction (e.g., neurogenic bladder)
- Ambulation generally preserved
- Survival into the 4th–7th decade
The HEMS phenotype is characterized by a distinctive pattern of hypomyelination on MRI involving structures that normally myelinate early in development. HEMS is currently considered a subtype of SPG2.
Pure SPG2 represents the mildest end of the PLP1-related disease spectrum.
Individuals with SPG2 typically present later in childhood or adulthood with:
- Progressive lower-limb spasticity
- Gait abnormalities or paraparesis
- Hyperreflexia
- Variable bladder dysfunction
- Mild ataxia or cognitive involvement in some cases
Unlike classic PMD, developmental milestones may be achieved within expected timeframes, and symptoms may initially resemble other hereditary spastic paraplegias.
Establishing diagnosis
Diagnosis of PMD
In male probands, the diagnosis of a PLP1-related disorder is established by identification of a hemizygous pathogenic (or likely pathogenic) variant in PLP1 by molecular genetic testing.
In female probands, the diagnosis of a PLP1-related disorder is usually established through neurologic signs, a family history of PLP1-related disorder, and a heterozygous pathogenic (or likely pathogenic) variant in PLP1 identified by molecular genetic testing.
When the phenotypic and laboratory findings suggest the diagnosis of a PLP1-related disorder, molecular genetic testing approaches should be considered in this order:
- targeted deletion/duplication analysis, to identify a PLP1 deletion/duplication
- single-gene testing, to detect missense, nonsense, and splice site variants and small intragenic deletions/insertions
- multigene panel that includes PLP1 and other genes of interest
When the phenotype is indistinguishable from many other inherited disorders characterized by motor and cognitive impairment, comprehensive genomic testing, for example exome sequencing or genome sequencing should be considered.
PMLD Clinical overview
Pelizaeus-Merzbacher-like disease (PMLD) shares many clinical and radiological features with PMD but is genetically distinct.
The condition is most commonly associated with pathogenic variants in GJC2 and is typically inherited in an autosomal recessive manner.
Affected individuals may present with:
Nystagmus
Developmental Delay
Hypotonia
Ataxia
MRI evidence of hypomyelination
Progressive spasticity
Because the clinical presentation can closely resemble PMD, molecular genetic testing is required to establish a definitive diagnosis.
Establishing diagnosis
Diagnosis of PMLD
The diagnosis of PMLD is established in a proband with suggestive clinical and neuroimaging findings and identification of biallelic pathogenic variants in GJC2 on molecular genetic testing.
When the clinical findings and brain MRI findings suggest the diagnosis of a PMLD, molecular genetic testing approaches should be considered in this order:
- single-gene testing of GJC2, including the noncoding exon 1; if only one pathogenic variant is found, perform gene-targeted deletion/duplication analysis
- multigene panel that includes GJC2 and other genes of interest
When the phenotype is indistinguishable from many other inherited leukodystrophies, molecular genetic testing approaches can include a combination of gene-targeted testing (multigene panel) or comprehensive genomic testing, which includes exome sequencing and genome sequencing.
Care management & referral considerations
PMD and PMLD are complex neurological disorders that often require multidisciplinary care throughout an individual’s life.
Management may involve collaboration between:
Neurologists
Clinical geneticists
Physical and occupational therapists
Speech-language pathologists
Rehabilitation specialists
Gastroenterologists
Pulmonologists
Palliative care teams
Primary care providers
Referral to specialist leukodystrophy centers or clinicians with experience managing hypomyelinating disorders may be beneficial, particularly in cases involving diagnostic uncertainty, complex symptom management, or consideration of clinical trial participation.
As individuals with PMD and PMLD transition into adulthood, coordinated transfer of care between pediatric and adult healthcare services helps ensure continuity of support and long-term management.
Resources for patients & families
The PMD Foundation provides educational resources, peer support opportunities, and community programs designed to help families navigate life with PMD and PMLD.
Clinical trials in PMD & PMLD
Research into PMD and PMLD continues to advance our understanding of disease mechanisms, natural history, biomarkers, and potential therapeutic approaches.
The PMD Foundation maintains information on current clinical trials, natural history studies, and research initiatives relevant to the PMD and PMLD communities.
Grant opportunities
The PMD Foundation provides research grants to accelerate the development of innovative diagnostics, biomarkers, and therapeutic strategies for PMD and PMLD. Our funding supports early-stage discovery research aimed at advancing promising therapeutics to clinical trials and patients. Grant cycles are announced periodically, and applications are reviewed by a scientific and community advisory board to ensure alignment with our mission and scientific rigor.
Our Scientific Advisory Board
The PMD Foundation’s Scientific Advisory Board is composed of experts in leukodystrophies, neurology, genetics, and rare disease research.
Our Board provides scientific guidance and helps ensure that the Foundation’s educational materials, research initiatives, and advocacy efforts reflect current evidence and best practice.
Further resources for HCPs
Information about PMD
Contact us
Looking for more HCP resources on PMD?
We welcome inquiries from healthcare professionals seeking information about PMD and PMLD, research initiatives, educational resources, or opportunities for collaboration.
Whether you are supporting a newly diagnosed family, looking for patient materials, or interested in ongoing research efforts, our team can help connect you with the information you need.
