Amyloid

File:Crossbeta.png

Amyloid refers to a diverse group of proteins that share a common structural feature: they form fibrils with a characteristic cross-β sheet conformation. These fibrils can aggregate and deposit in various tissues and organs, leading to a range of diseases known as amyloidosis.

Structure

Amyloid fibrils are composed of polypeptide chains that align in a parallel or antiparallel fashion, forming a β-sheet structure. This arrangement is stabilized by hydrogen bonds, resulting in highly ordered, insoluble fibrils. The cross-β sheet structure is a hallmark of amyloid fibrils and can be detected using techniques such as X-ray crystallography and electron microscopy.

Types of Amyloid

There are several types of amyloid proteins, each associated with different diseases:

• Amyloid beta (Aβ): Associated with Alzheimer's disease.
• Transthyretin (TTR): Linked to familial amyloid polyneuropathy and senile systemic amyloidosis.
• Serum amyloid A (SAA): Involved in secondary amyloidosis.
• Immunoglobulin light chain (AL): Found in primary amyloidosis.

Diseases

Amyloid deposits can disrupt normal tissue function, leading to various diseases collectively known as amyloidosis. Some of the major forms of amyloidosis include:

• Alzheimer's disease: Characterized by the accumulation of amyloid beta plaques in the brain.
• Primary amyloidosis: Caused by the deposition of immunoglobulin light chains.
• Secondary amyloidosis: Results from chronic inflammatory conditions, leading to the deposition of serum amyloid A.
• Familial amyloid polyneuropathy: A hereditary form of amyloidosis caused by mutations in the transthyretin gene.

Diagnosis

The diagnosis of amyloidosis typically involves a combination of clinical evaluation, imaging studies, and biopsy. Congo red staining of tissue samples is a common method used to identify amyloid deposits, which exhibit apple-green birefringence under polarized light. Advanced imaging techniques such as positron emission tomography (PET) and magnetic resonance imaging (MRI) can also aid in the diagnosis.

Treatment

Treatment options for amyloidosis depend on the type and extent of the disease. They may include:

• Chemotherapy: Used in cases of primary amyloidosis to reduce the production of amyloidogenic light chains.
• Liver transplantation: Considered for familial amyloid polyneuropathy to replace the source of mutant transthyretin.
• Supportive care: Aimed at managing symptoms and improving quality of life.

Research

Ongoing research is focused on understanding the mechanisms of amyloid formation and developing targeted therapies. Potential strategies include the use of small molecules to inhibit fibril formation, immunotherapy to promote amyloid clearance, and gene therapy to correct underlying genetic defects.

See also

• Amyloidosis
• Alzheimer's disease
• Transthyretin
• Immunoglobulin light chain

External links

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