Overview
X-linked lymphoproliferative disease due to SAP deficiency, also known as XLP1 or Duncan disease, is a rare inherited immune system disorder that affects almost exclusively males. It is caused by changes (mutations) in the SH2D1A gene, which provides instructions for making a protein called SAP (SLAM-associated protein). SAP plays a critical role in helping immune cells — especially T cells and NK cells — work properly and communicate with each other. In XLP1, the immune system fails to control a common virus called Epstein-Barr virus (EBV), also known as the virus that causes mono (mononucleosis). When boys with XLP1 are exposed to EBV, their immune system can go into dangerous overdrive, leading to a life-threatening condition called hemophagocytic lymphohistiocytosis (HLH), where immune cells start attacking the body's own tissues and organs. Even without EBV infection, affected individuals are at high risk for developing low antibody levels (hypogammaglobulinemia) and certain blood cancers called lymphomas. The main treatments include immunoglobulin replacement therapy to boost antibody levels, chemotherapy and steroids to control HLH episodes, and hematopoietic stem cell transplantation (bone marrow transplant), which is currently the only potentially curative treatment. Early diagnosis and transplant before EBV exposure offer the best outcomes.
Also known as:
Key symptoms:
Severe or life-threatening reaction to Epstein-Barr virus (EBV) infectionProlonged high fever that does not go awayEnlarged spleen and liverSwollen lymph nodesLow blood counts (anemia, low platelets, low white blood cells)Frequent or unusual infections due to low antibody levelsAbnormal immune cell activity attacking the body's own organs (HLH)Lymphoma (a type of blood cancer)Jaundice (yellowing of skin and eyes)Extreme fatigue and weaknessEasy bruising or bleedingNeurological symptoms such as confusion or seizures during HLH episodes
X-linked recessive
Carried on the X chromosome; typically affects males more than females
Childhood
Begins in childhood, roughly ages 1 to 12
Treatments
No FDA-approved treatments are currently listed for X-linked lymphoproliferative disease due to SAP deficiency.
View clinical trials →Clinical Trials
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Specialists
View all specialists →No specialists are currently listed for X-linked lymphoproliferative disease due to SAP deficiency.
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 X-linked lymphoproliferative disease due to SAP deficiency.
Community
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Caregiver Resources
NORD Caregiver Resources
Support, advocacy, and financial assistance for caregivers of rare disease patients.
Mental Health Support
Rare disease caregiving can be isolating. Connect with counseling and peer support.
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.Should my son have a bone marrow transplant, and how soon should we plan for it?,How do we find out if other male relatives in our family might also have XLP1?,What steps should we take to protect my son from EBV infection before transplant?,What are the signs of HLH, and what should I do if I think it is happening?,Does my son need regular IVIG infusions, and how will we manage those?,Are there any clinical trials or new treatments we should consider?,What long-term monitoring will my son need after a bone marrow transplant?
Common questions about X-linked lymphoproliferative disease due to SAP deficiency
What is X-linked lymphoproliferative disease due to SAP deficiency?
X-linked lymphoproliferative disease due to SAP deficiency, also known as XLP1 or Duncan disease, is a rare inherited immune system disorder that affects almost exclusively males. It is caused by changes (mutations) in the SH2D1A gene, which provides instructions for making a protein called SAP (SLAM-associated protein). SAP plays a critical role in helping immune cells — especially T cells and NK cells — work properly and communicate with each other. In XLP1, the immune system fails to control a common virus called Epstein-Barr virus (EBV), also known as the virus that causes mono (mononucle
How is X-linked lymphoproliferative disease due to SAP deficiency inherited?
X-linked lymphoproliferative disease due to SAP deficiency follows a x-linked recessive inheritance pattern. Genetic counseling can help families understand recurrence risk and testing options.
At what age does X-linked lymphoproliferative disease due to SAP deficiency typically begin?
Typical onset of X-linked lymphoproliferative disease due to SAP deficiency is childhood. Age of onset can vary across affected individuals.