Leading Science in Rare Diseases, Every Day

With more than three decades of research and nearly 20 years of real-world evidence, we’ve proven what is possible in a variety of rare diseases and devastating conditions across neurology, hematology, nephrology, and metabolics. This experience drives us to continue advancing our science to help patients and families fully live their best lives.


Our Foundation in Complement

Our pioneering legacy in rare diseases is rooted in being the first to translate the complex biology of the complement system into transformative medicines. The scientific community was initially skeptical about complement inhibition, but our scientists led the way. Their work has helped many people living with rare diseases reclaim their lives. Today, we continue innovating to accelerate the discovery and development of new life-changing therapies for even more patients.


What Is the Complement System?

Part of the immune system and essential to the body’s defense against infection.

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The complement system is a part of the immune system and is essential to the body’s defense against infection. It is made up of three unique pathways.
Each pathway activates a cascade of protein reactions that trigger immune response to fight invaders.
When the body is healthy, these proteins form a complex network to detect and help eliminate bacteria, viruses, and dead cells.
However, when the system is thrown out of balance, or dysregulated, the same proteins can trigger a dangerous, uncontrolled cascade of reactions that attack healthy cells and tissues.
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Understanding the C5 Protein
The complement system’s cascade of molecular reactions ultimately leads to activation of the C5 protein. Watch to learn more about the role of C5.

Understanding the FD Protein
Factor D, a complement system protein, plays a key role in activating the alternative pathway, which amplifies the complement response. Watch to learn more.

Understanding the Properdin Protein
Properdin is critical in stabilizing key complement protein complexes, which helps to regulate alternative pathway activation and amplification. Watch to learn more.

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Pioneering Complement Science

Our scientists blazed a trail in complement inhibition research. Hear from a few of our pioneers who played a role in translating this research into transformational medicines for rare diseases and why they persisted.

Driving Complement Research Forward

Learn about Alexion’s ongoing research to build upon our deep expertise in complement biology, and hear about our work to advance the next generation of complement inhibitors to help more patients.

Complement- Mediated Diseases

Dysregulation of the complement system is a driver of many diseases. We remain focused on innovating to translate the science of complement inhibition into new medicines.


Atypical Hemolytic Uremic Syndrome (aHUS)

A rare, chronic, and potentially life-threatening disease caused by complement dysregulation. aHUS is a type of complement-mediated thrombotic microangiopathy (CM-TMA) that can cause severe progressive organ damage, often of the kidneys, or death.


Dermatomyositis (DM)

A progressive, autoimmune, inflammatory condition that causes damage in the blood vessels under the skin and in the muscles. This damage leads to skin changes, including a rash around the eyelids, face and chest, red bumps around the joints, difficulty swallowing and progressive muscle weakness in the arms and legs. 


Geographic Atrophy (GA)

A chronic and progressive eye disease that causes degeneration of the portion of the retina responsible for central and color vision, leading to visual impairment and loss of mobility. A major cause of blindness, GA is difficult to diagnosis due to a low rate of progression and subtle symptoms. People over the age of 75 are disproportionally impacted by the disease. 


Generalized Myasthenia Gravis (gMG)

A rare, debilitating, neuromuscular autoimmune disorder characterized by a loss of muscle function and severe weakness. Symptoms include slurred speech, double vision, droopy eyelids, lack of balance, difficulty swallowing or choking, extreme fatigue, and respiratory failure.  

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Text: What is Generalized Myasthenia Gravis (gMG)?


Hematopoietic Stem Cell Transplant-Associated Thrombotic Microangiopathy (HSCT-TMA)

A type of complement-mediated thrombotic microangiopathy (CM-TMA) that can present during or after hematopoietic stem cell transplantation (HSCT). This severe, and often lethal, condition occurs when factors associated with HSCT (including conditioning regimens, immunosuppressant therapies, and infection) induce complement system overactivation or unmask complement dysregulation that fuels an attack on cells, including endothelial cells that line blood vessels.

IgA Nephropathy

Immunoglobulin A (IgA) Nephropathy

A renal disease in which locally deposited immune complexes (e.g., immunoglobulin G (IgG) and antigen) lead to activation of the complement cascade and endothelial organ damage, leading to end-stage renal disease (kidney failure), requiring dialysis or transplant.


Lupus Nephritis (LN)

A severe complication of systemic lupus erythematosus (SLE) in which deposits of immune complexes (e.g., immunoglobulin G (IgG) and antigen) accumulate in the kidney and may lead to injury through complement activation. Up to 30% of patients progress to end-stage renal disease (kidney failure) within 15 years, requiring dialysis or transplant.


Neuromyelitis Optica Spectrum Disorder (NMOSD)

A rare, autoimmune disorder of the central nervous system that affects the optic nerve and spinal cord, more commonly in women. The disorder is characterized by unpredictable attacks, known as relapses, that result in cumulative disability, including vision loss, paralysis, and sometimes premature death.

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Text: What is Neuromyelitis Optica Spectrum Disorder (NMOSD)?


Paroxysmal Nocturnal Hemoglobinuria (PNH)

A rare, chronic, progressive, debilitating, and potentially life-threatening blood disorder characterized by complement-mediated intravascular hemolysis (destruction of red blood cells in the blood vessels) and thrombosis (blood clots), due to terminal complement activation. Thrombosis can be life-threatening and is the leading cause of death in this disease.  PNH can lead to serious health complications, including damage to vital organs, such as kidneys and lungs.

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Paroxysmal Nocturnal Hemoglobinuria With Extravascular Hemolysis (PNH-EVH)

PNH is a rare, chronic, progressive, debilitating, and potentially life-threatening blood disorder characterized by complement-mediated intravascular hemolysis (destruction of red blood cells in the blood vessels) and thrombosis (blood clots), due to terminal complement activation. EVH can sometimes occur in PNH patients when treated with C5 inhibitors as the now surviving PNH red blood cells are marked by other proteins in the complement system for removal by the spleen and liver. PNH patients with EVH may remain anemic and may require occasional blood transfusions.

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People Behind The Science

Our science wouldn’t be possible without our team of passionate, driven, and dedicated individuals who make up Alexion R&D. Hear from a few of our scientists and leaders about what makes our R&D unique, what motivates them, and how we work each day to help transform patient lives.

SungKwon Kim

SungKwon Kim, Ph.D.

Raj Pradhan

Rajendra Pradhan, Ph.D.

Anita Hill

Anita Hill, M.D., Ph.D.

Paul Tamburini

Paul Tamburini, Ph.D.

Susan Faas

Susan Faas, Ph.D.

Laura Gault

Laura Gault, M.D.

Moshe Vardi

Moshe Vardi, M.D.

Sharon Barr

Sharon Barr, Ph.D.


Diversifying for the Future

Our mission of transforming the lives of people living with rare diseases guides our research and development efforts. We’re applying our expertise beyond complement to deliver innovations for even more patients.


Amyloid Light Chain (AL) Amyloidosis

Amyloid light chain (AL) amyloidosis is a rare disease where proteins that function as antibodies, also known as immunoglobulins, are produced abnormally by defective plasma cells in the bone marrow. These abnormal proteins misfold and clump together to form toxic amyloids and may deposit in tissues and/or organs. Amyloid can buildup in many organs, particularly in the heart and kidneys, which can result in significant organ damage and organ failure that may ultimately be fatal. 

Alexion’s research teams are working to uncover new insights about AL amyloidosis with the goal of delivering a transformational medicine to people living with the condition.

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Text: What is AL Amyloidosis?


We are dedicated to building upon our trailblazing science in rare disease to translate emerging science into transformational medicines for even more patients.

AL Amyloidosis

Amyloid Light Chain (AL) Amyloidosis

A rare disease where abnormal antibody (immunoglobulin) proteins are produced by defective plasma cells in the bone marrow. These abnormal proteins misfold and clump together to form amyloids and may deposit in tissues and/or organs. Amyloid buildup in organs, particularly in the heart and kidneys, can result in significant organ damage and organ failure that may ultimately be fatal.

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What is AL Amyloidosis?


Transthyretin Amyloidosis Cardiomyopathy (ATTR-CM)

A progressive, rare disease where transthyretin (TTR) proteins, which are responsible for transporting thyroid hormone and vitamin A in the blood, become unstable, break into parts, and form protein or “amyloid” deposits in the heart. Typical symptoms are similar to those associated with heart failure, including shortness of breath, edema (swelling of the legs), and atrial fibrillation and may be fatal if not treated.


Hypophosphatasia (HPP)

A rare, genetic disease characterized by impaired bone mineralization (“calcification”), the process that hardens and strengthens bones and teeth. This can lead to poor growth and development, deformity of bones, muscle weakness, pain, premature loss of teeth with the root intact, and other skeletal and non-skeletal abnormalities. As a result, the disease can have a debilitating impact, including loss of physical function.

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Neurofibromatosis Type 1 (NF1) Plexiform Neurofibromas (PN)

A rare, progressive, genetic condition characterized by non-malignant (non-cancerous) tumors called plexiform neurofibromas (PN) that develop in the brain, and along the spinal cord and nerves. Potential complications of PNs include itching, physical deformities, and organ dysfunction, which may lead to trouble breathing, visual impairment, and bladder and bowel problems, among other challenges. Although PN may start as non-malignant, a small proportion (~10%) will later in life become malignant (cancer).

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Wilson Disease

Wilson Disease

A rare and progressive genetic condition in which the body’s pathway for removing excess copper is compromised. If copper levels are not effectively managed, copper will accumulate, over time, to toxic levels in the liver, brain and other organs, leading to liver disease and neurological, and psychiatric symptoms that greatly impact a patient’s life.

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