CD55 deficiency

A rare genetic disorder affecting the complement system

Classification	ICD-10: D84.1 OMIM: 612840 MeSH: D000014
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CD55 deficiency, also known as CHAPLE syndrome (complement hyperactivation, angiopathic thrombosis, and protein-losing enteropathy), is a rare genetic disorder that affects the immune system. It is characterized by a deficiency in the CD55 protein, which plays a crucial role in regulating the complement system, a part of the immune system that enhances the ability of antibodies and phagocytic cells to clear microbes and damaged cells.

Genetics

CD55 deficiency is inherited in an autosomal recessive manner. This means that an individual must inherit two copies of the defective gene, one from each parent, to manifest the disease. The gene responsible for CD55 deficiency is located on chromosome 1q32.2 and encodes the CD55 protein, also known as decay-accelerating factor (DAF).

Autosomal recessive inheritance pattern

Pathophysiology

The CD55 protein is a glycoprotein that regulates the complement system by inhibiting the formation of the C3 and C5 convertases, which are crucial for the activation of the complement cascade. In individuals with CD55 deficiency, the lack of functional CD55 leads to uncontrolled activation of the complement system. This hyperactivation can result in angiopathy, thrombosis, and protein-losing enteropathy, which are the hallmark features of CHAPLE syndrome.

Clinical Features

Patients with CD55 deficiency typically present with symptoms related to the overactivation of the complement system. These symptoms may include:

• Recurrent gastrointestinal issues such as diarrhea and abdominal pain due to protein-losing enteropathy.
• Increased risk of thrombosis, which can lead to complications such as deep vein thrombosis or pulmonary embolism.
• Angiopathic manifestations, which may include vasculitis and other vascular abnormalities.

Diagnosis

The diagnosis of CD55 deficiency is based on clinical evaluation, laboratory tests, and genetic testing. Laboratory tests may show evidence of complement activation, such as low levels of complement components C3 and C4. Genetic testing can confirm the diagnosis by identifying mutations in the CD55 gene.

Treatment

There is currently no cure for CD55 deficiency, and treatment is primarily supportive. Management strategies may include:

• Use of anticoagulants to prevent thrombosis.
• Nutritional support to manage protein-losing enteropathy.
• Immunosuppressive therapy to control complement activation.

Prognosis

The prognosis for individuals with CD55 deficiency varies depending on the severity of the symptoms and the effectiveness of the management strategies. Early diagnosis and appropriate treatment can improve the quality of life and reduce the risk of complications.

Related pages

• Complement system
• Genetic disorder
• Autosomal recessive disorder