CD55 deficiency

Autosomal recessive - en

CD55 Deficiency, also known as DAF Deficiency or Decay-Accelerating Factor Deficiency, is a rare genetic disorder that affects the immune system. This condition is characterized by the body's inability to regulate the complement system, a part of the immune system that enhances the ability of antibodies and phagocytic cells to clear pathogens from an organism. CD55, a protein encoded by the CD55 gene, plays a crucial role in protecting the body's cells from being attacked by its own complement system.

Overview

CD55 deficiency leads to an increased vulnerability of the body's cells to attack by the complement system, particularly the red blood cells, which can result in conditions such as Paroxysmal Nocturnal Hemoglobinuria (PNH) and atypical Hemolytic Uremic Syndrome (aHUS). These conditions are characterized by the destruction of red blood cells, blood clots, and impaired kidney function, respectively.

Causes

The deficiency is caused by mutations in the CD55 gene, which provides instructions for making the CD55 protein. This protein is essential for controlling the complement system by preventing the formation of a group of proteins known as the membrane attack complex (MAC) on the surface of the body's own cells. Without sufficient CD55, cells become more susceptible to damage by the complement system.

Symptoms

Symptoms of CD55 deficiency can vary widely among affected individuals but may include:

• Fatigue
• Hemoglobinuria (the presence of hemoglobin in urine)
• Abdominal pain
• Anemia
• Thrombosis (blood clots)
• Kidney dysfunction

Diagnosis

Diagnosis of CD55 deficiency involves a combination of clinical evaluation and laboratory tests. These tests may include flow cytometry to measure the expression of CD55 on the surface of blood cells, genetic testing to identify mutations in the CD55 gene, and assays to assess the activity of the complement system.

Treatment

There is no cure for CD55 deficiency, but treatment focuses on managing symptoms and preventing complications. Treatment options may include:

• Blood transfusions to treat anemia
• Medications to control the complement system, such as eculizumab, a monoclonal antibody that inhibits the complement protein C5
• Anticoagulants to prevent thrombosis
• Bone marrow transplantation in severe cases

Prognosis

The prognosis for individuals with CD55 deficiency varies depending on the severity of the condition and the effectiveness of the treatment. With appropriate management, many individuals can lead relatively normal lives. However, they may require ongoing treatment to manage symptoms and prevent complications.

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