What Is Jordan’s Syndrome? Symptoms, Causes, and Diagnosis

Jordan’s syndrome is a rare neurodevelopmental disorder caused by spontaneous mutations in a gene called PPP2R5D, which encodes a component of an important cellular enzyme known as Protein Phosphatase 2A (PP2A).¹ The condition, also referred to in the medical literature as PPP2 syndrome type R5D or Houge-Janssens syndrome type 1, typically presents in early childhood with a combination of developmental delays, an unusually large head, low muscle tone, seizures, and features associated with autism. Because it was only identified in the mid-2010s and remains extremely rare, many families encounter a long diagnostic journey before receiving an answer.

How It Was Identified

The genetic basis of Jordan’s syndrome was established through whole-exome sequencing, a technique that reads the protein-coding portions of a person’s DNA. An early landmark study identified four distinct mutations in PPP2R5D across seven unrelated individuals who shared a recognizable pattern of intellectual disability, large head circumference, low muscle tone, seizures, and certain facial features.² Those findings were published in 2015 and gave the first solid evidence that PPP2R5D mutations cause a distinct syndrome rather than isolated, unrelated symptoms. The name “Jordan’s syndrome” comes from Jordan Lang, a child diagnosed with the condition whose family helped raise awareness and connect other affected families.

Since that initial discovery, the number of known cases has grown steadily. A recent literature review compiled 213 reported cases worldwide, though the true number of affected individuals is likely higher because many go undiagnosed or are diagnosed under different labels before genetic testing reveals the underlying cause.³

The Genetic Cause

Jordan’s syndrome results from a single-letter change in the PPP2R5D gene, a type of mutation known as a missense variant. In almost every documented case, the mutation is “de novo,” meaning it arises spontaneously in the child rather than being inherited from either parent.² Only one copy of the gene needs to carry the mutation to cause the disorder. This matters for families because it means most parents of an affected child have no increased risk of having another child with the same condition, and they themselves do not carry the variant.

Several different mutations within PPP2R5D have been linked to the syndrome, but they cluster in specific regions of the gene that are critical for the protein’s function. One of the most commonly reported is c.598G>A, which changes a glutamic acid to a lysine at a specific position in the protein. Two pediatric cases carrying this exact variant were recently detailed in a clinical report, and it appears consistently across the broader literature as a recurrent hotspot.³

The fact that mutations are not scattered randomly across the gene but concentrate at a few positions is actually informative. It tells researchers that these particular amino acids are indispensable for how the protein folds, interacts with partner proteins, and carries out its enzymatic work.

What PP2A Does and Why the Mutations Matter

PP2A is one of the most abundant enzymes in cells, and its job is to remove phosphate groups from other proteins. Phosphate groups act like molecular on/off switches: adding one can activate a protein, and removing one can deactivate it. PP2A is responsible for flipping many of these switches off at the right time, which is essential for keeping cell growth, division, and signaling in check. The PPP2R5D gene encodes a regulatory subunit (called B56δ) that helps steer the enzyme toward the correct targets.

When a Jordan’s syndrome mutation hits B56δ, the enzyme does not simply stop working. Instead, the mutant subunit assembles into enzyme complexes that are structurally intact but functionally impaired. Research has shown that some mutant B56δ proteins can still bind to one partner subunit but lose the ability to bind another, or they bind a catalytically crippled version of the enzyme’s active component.⁴ The result is a “dominant-negative” effect: the broken copies actively interfere with the healthy copies rather than simply being absent. This was further supported by neuronal studies showing that neurons completely lacking PPP2R5D did not display the same overgrowth seen in neurons carrying the mutations, confirming that the problem is not a simple loss of the protein.⁵

One specific mutation, E198K, has received particular attention. Computational modeling suggests that it disrupts a critical interaction between the B56δ subunit and the catalytic core of the enzyme, effectively releasing a brake on phosphatase activity in some contexts while suppressing it in others.⁶ Genotype-phenotype analysis has found that this variant, E198K, tends to produce some of the more severe clinical features, likely because it causes the greatest disruption to the enzyme’s ability to bind its catalytic partner.⁷

Recognizing the Symptoms

Jordan’s syndrome produces a constellation of symptoms rather than one defining feature. There is a broad spectrum of severity, and each person typically has only a subset of all reported features.¹ That variability can make the condition tricky to spot clinically, especially for physicians unfamiliar with it. The most commonly reported features include:

Macrocephaly: An unusually large head circumference, often noticeable in infancy, is one of the most consistent findings across reported cases.
Global developmental delay: Children typically reach motor and language milestones later than their peers. The degree of intellectual disability ranges from mild to severe.
Hypotonia: Low muscle tone is frequently present from birth, which can contribute to feeding difficulties in the newborn period and delayed motor skills later.
Seizures: Epilepsy affects a significant proportion of individuals, with onset often occurring in the first years of life.
Autism-related features: Many children display social and sensory challenges associated with autism spectrum disorder, including difficulty with social interaction and heightened sensitivity to sounds or textures.
Attention difficulties: Problems with focus and attention are commonly observed alongside the developmental features.
Eye abnormalities: Ophthalmological issues, including strabismus (crossed eyes) and other visual impairments, are reported in many affected individuals.
Sleep problems: Disordered sleep, such as difficulty falling asleep or staying asleep, adds to the daily management burden for families.
Feeding challenges: Difficulties with feeding are common in infancy and may persist in milder forms as children grow.

Not every child with Jordan’s syndrome will have all of these features. Some individuals have relatively mild developmental delays and no seizures, while others face more complex medical needs. The specific mutation a person carries partly explains this variation: as noted in the section on genetics, some variants are associated with more severe outcomes than others.⁷

How It Is Diagnosed

There is no blood test or imaging scan that specifically identifies Jordan’s syndrome. Diagnosis depends on genetic testing, typically whole-exome sequencing or targeted gene panels that include PPP2R5D. In practice, many families arrive at a diagnosis only after a child has been evaluated for unexplained developmental delay, large head size, or seizures, and a geneticist orders broad-spectrum genetic testing as part of the workup.

Before genetic testing became widely accessible, children with the condition were often given general labels like “unspecified intellectual disability” or “autism with macrocephaly.” Even today, some individuals go years without a molecular diagnosis simply because their physicians have not encountered the syndrome before. The two recently reported pediatric cases, both carrying the same PPP2R5D variant confirmed as de novo, illustrate a common diagnostic path: the children were initially evaluated for developmental delay and seizures, and the specific diagnosis came only after exome sequencing.³

Once a pathogenic PPP2R5D variant is found, clinical evaluation typically expands to screen for associated features the family may not yet have recognized, such as eye abnormalities or subtle seizure activity on an EEG. Published care guidelines based on data from roughly 100 individuals recommend a structured evaluation covering neurology, ophthalmology, developmental assessment, and sleep studies so that management can be tailored to each person’s specific combination of symptoms.¹

The Broader Family of PP2A Disorders

Jordan’s syndrome does not exist in isolation. It belongs to a group of overlapping conditions caused by mutations in different genes that all encode subunits of the same PP2A enzyme. Mutations in PPP2R1A (encoding the A-alpha scaffolding subunit) cause a related disorder now classified as Houge-Janssens syndrome type 2, and mutations in PPP2CA (encoding the catalytic subunit itself) cause type 3.⁸ More recently, pathogenic variants in PPP2R5C, which encodes a different regulatory subunit, have also been added to the spectrum.

All of these conditions share core features: developmental delay, intellectual disability, and various neurological symptoms. Their overlap makes sense biologically because each mutated gene disrupts the same enzyme, just at a different structural point. Researchers have proposed grouping them under the umbrella term “PP2A-related neurodevelopmental disorders” to reflect this shared mechanism.⁹ For families, this grouping matters because advances in understanding one PP2A disorder can inform treatment strategies for the others.

That said, the specific subunit affected does influence the clinical picture. PPP2R1A mutations, for example, can produce a somewhat different balance of symptoms compared to PPP2R5D mutations, even though the broad strokes are similar. The degree of biochemical dysfunction at the enzyme level correlates with phenotypic severity across these related conditions, reinforcing that the precise nature of the molecular disruption determines how the disorder manifests in each individual.⁹

A Signaling Pathway That Could Be Targeted

One of the more promising avenues of research involves the mTOR signaling pathway, a major cellular growth-control system. Proteomic studies of cells carrying Jordan’s syndrome mutations have found that a protein called ribosomal protein S6 (RPS6) is excessively phosphorylated, which is a hallmark of overactive mTOR signaling. When researchers treated these cells with rapamycin, a well-known mTOR inhibitor already used in other medical contexts, the excessive phosphorylation was suppressed.¹⁰

This finding is significant for two reasons. First, it identifies a druggable pathway. Rapamycin and its derivatives (known as rapalogs) are already FDA-approved for other conditions, which could shorten the timeline to clinical trials if the approach proves viable in animal models and early-phase human studies. Second, the proteomic data revealed that different PPP2R5D mutations may activate mTOR through different upstream routes. One variant appeared to work through a kinase called AKT, while another reached the same endpoint through an AKT-independent route.¹⁰ Understanding these distinct molecular paths could eventually matter for personalizing treatment based on each patient’s specific mutation.

Disease Modeling With Patient-Derived Neurons

Because Jordan’s syndrome is so rare, large clinical trials are impractical in the near term. Researchers have turned instead to laboratory models built from patients’ own cells. In one approach, skin cells from a patient carrying the E198K mutation were reprogrammed into induced pluripotent stem cells (iPSCs) and then coaxed into becoming brain cells, specifically midbrain neurons that produce dopamine. This is particularly relevant because PPP2R5D mutations have been linked to early-onset parkinsonism, a condition characterized by the loss of dopamine-producing neurons. Using gene editing, the team also created an “isogenic control” cell line with the mutation corrected, giving them a side-by-side comparison to isolate the mutation’s effects.¹¹

A separate group took a complementary approach, deriving neurons from patients with different PPP2R5D variants and observing that the mutant neurons showed abnormal overgrowth of neurites (the branches neurons extend to communicate with each other). When the researchers selectively silenced the mutant copy of the gene while leaving the healthy copy intact, the overgrowth phenotype was reversed.⁵ This allele-specific knockdown strategy is early-stage, but it represents a potential therapeutic concept: if you could silence just the bad copy in a patient’s brain, the healthy copy could function normally.

Early-Onset Parkinsonism

One of the more unexpected findings to emerge from the study of Jordan’s syndrome is an association with early-onset Parkinson disease. While the hallmark features of the condition are developmental, some individuals with PPP2R5D mutations have developed parkinsonian symptoms at ages far younger than typical for Parkinson disease.⁵ This connection was not predicted from the initial discovery of the syndrome and underscores how a single gene can influence the brain across different life stages. It also raises practical questions about long-term neurological monitoring for individuals with the condition, particularly as the first generation of diagnosed patients moves into adolescence and adulthood.

The iPSC-derived midbrain neuron models described earlier are directly relevant here, because they allow researchers to study dopamine-pathway deficits in a dish rather than waiting decades for clinical data to accumulate. If specific mutations carry a higher risk of parkinsonism, that information could guide surveillance recommendations for affected families.

Living With the Diagnosis

There is currently no cure for Jordan’s syndrome, and management is symptom-based. Seizures are treated with standard anti-epileptic medications, though some families report that finding the right drug or combination takes time. Physical and occupational therapy address hypotonia and motor delays. Speech therapy is commonly needed, and many children benefit from behavioral supports tailored to autism-related social and sensory challenges. Sleep issues may require a combination of behavioral strategies and, in some cases, medication.

The published care guidelines drawn from data on roughly 100 individuals provide a framework that many families and clinicians have found helpful, particularly because they lay out which specialists should be involved and how often evaluations should occur.¹ Having a named diagnosis, rather than a vague label, also opens doors to educational accommodations and disability services that require documentation of a medical condition.

Parent-driven organizations, most notably the Jordan’s Guardian Angels Foundation, have played an outsized role in connecting families, funding research, and building a patient registry. For a condition this rare, patient registries are not just nice to have; they are the foundation on which clinical research depends. Every new case that is documented and shared adds to the collective understanding of the syndrome’s natural history and helps researchers design meaningful studies.