Overview
Primary hypereosinophilic syndrome (HES) is a rare blood disorder in which the body produces too many eosinophils, a type of white blood cell that normally helps fight infections and parasites. In this condition, eosinophil levels stay dangerously high for a prolonged period (typically above 1,500 cells per microliter of blood for at least six months), and these excess cells can infiltrate and damage organs throughout the body. The term 'primary' means the overproduction of eosinophils is driven by a problem within the blood-forming cells themselves, often linked to a genetic change in those cells, rather than being caused by allergies, parasites, or other secondary triggers. The organs most commonly affected include the heart, lungs, skin, nervous system, and gastrointestinal tract. Symptoms vary widely depending on which organs are involved but can include fatigue, skin rashes, cough, shortness of breath, abdominal pain, and numbness or tingling in the hands and feet. Heart damage (eosinophilic myocarditis or endomyocardial fibrosis) is one of the most serious complications and can be life-threatening if not treated. Treatment has improved significantly in recent years. Corticosteroids like prednisone are often the first-line therapy to reduce eosinophil counts. For patients whose disease is driven by specific genetic changes such as the FIP1L1-PDGFRA fusion gene, targeted therapies like imatinib can be highly effective. Newer biologic therapies, including mepolizumab (Nucala), which targets interleukin-5, have been approved for certain forms of HES. The treatment approach depends on the underlying cause and severity of organ involvement.
Also known as:
Key symptoms:
Persistent fatigue and weaknessSkin rashes or itchy skinCough that does not go awayShortness of breathAbdominal pain or diarrheaNumbness or tingling in hands and feetFeverMuscle aches and joint painSwelling of the legs or feetChest pain or heart problemsWeight loss without tryingNight sweatsVision changesBlood clotsEnlarged spleen or liver
Sporadic
Usually appears on its own, not inherited from a parent
Adult
Begins in adulthood (age 18 or older)
Treatments
No FDA-approved treatments are currently listed for Primary hypereosinophilic syndrome.
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Treatment Centers
8 centersBaylor College of Medicine Rare Disease Center ↗
Baylor College of Medicine
📍 Houston, TX
🏥 NORDStanford Medicine Rare Disease Center ↗
Stanford Medicine
📍 Stanford, CA
🔬 UDNNIH Clinical Center Undiagnosed Diseases Program ↗
National Institutes of Health
📍 Bethesda, MD
🔬 UDNUCLA UDN Clinical Site ↗
UCLA Health
📍 Los Angeles, CA
🔬 UDNBaylor College of Medicine UDN Clinical Site ↗
Baylor College of Medicine
📍 Houston, TX
🔬 UDNHarvard/MGH UDN Clinical Site ↗
Massachusetts General Hospital
📍 Boston, MA
🏥 NORDMayo Clinic Center for Individualized Medicine ↗
Mayo Clinic
📍 Rochester, MN
👤 Mayo Clinic Center for Individualized Medicine
🏥 NORDUCLA Rare Disease Day Program ↗
UCLA Health
📍 Los Angeles, CA
Travel Grants
No travel grants are currently matched to Primary hypereosinophilic syndrome.
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Caregiver Resources
NORD Caregiver Resources
Support, advocacy, and financial assistance for caregivers of rare disease patients.
Mental Health Support
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Family & Caregiver Grants
Financial assistance programs specifically for caregivers of rare disease patients.
Social Security Disability
Learn how rare disease patients may qualify for SSDI/SSI benefits.
Questions for your doctor
Bring these to your next appointment
- Q1.Has testing been done for the FIP1L1-PDGFRA fusion gene, and what does my genetic result mean for treatment?,Which of my organs are currently affected, and how severe is the damage?,What treatment do you recommend, and what are the potential side effects?,How often will I need blood tests and follow-up appointments?,Are there any clinical trials available for my specific type of HES?,What emergency symptoms should I watch for that would require immediate medical attention?,Will I need to take medication for the rest of my life?
Common questions about Primary hypereosinophilic syndrome
What is Primary hypereosinophilic syndrome?
Primary hypereosinophilic syndrome (HES) is a rare blood disorder in which the body produces too many eosinophils, a type of white blood cell that normally helps fight infections and parasites. In this condition, eosinophil levels stay dangerously high for a prolonged period (typically above 1,500 cells per microliter of blood for at least six months), and these excess cells can infiltrate and damage organs throughout the body. The term 'primary' means the overproduction of eosinophils is driven by a problem within the blood-forming cells themselves, often linked to a genetic change in those c
How is Primary hypereosinophilic syndrome inherited?
Primary hypereosinophilic syndrome follows a sporadic inheritance pattern. Genetic counseling can help families understand recurrence risk and testing options.
At what age does Primary hypereosinophilic syndrome typically begin?
Typical onset of Primary hypereosinophilic syndrome is adult. Age of onset can vary across affected individuals.
Which specialists treat Primary hypereosinophilic syndrome?
7 specialists and care centers treating Primary hypereosinophilic syndrome are listed on UniteRare, sourced from ClinicalTrials.gov principal investigators, published research, and the NPPES NPI registry.