Definition
Amyloidosis is a rare disease in which normal body proteins deposit abnormally in tissues and organs. These deposits, known as “amyloid”, can disrupt the function of affected organs. There are different types of amyloidosis, depending on the protein involved.
Lysozyme is a protein naturally present in our body. It plays an important role in immune defense, helping to destroy certain bacteria. Lysozyme is found in fluids such as tears, saliva and mucus.
Lysozyme amyloidosis (ALys) is a rare hereditary form of amyloidosis in which amyloid deposits are predominantly made up of a mutated, abnormally folded lysozyme protein.
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Epidemiology
Lysozyme amyloidosis is linked to autosomal dominant mutations.
These mutations alter the structure of the lysozyme protein, an enzyme normally involved in antimicrobial defense (present in tears, saliva and other bodily secretions).
Genetic
Lysozyme amyloidosis is linked to autosomal dominant mutations in the LYZ gene.
These mutations modify the structure of the lysozyme protein, causing it to fold abnormally in the body. The mutation is often found in large families, as there is a 50% risk of passing it on from parent to child.
Pathophysiology
Lysozyme amyloidosis is linked to mutations that render lysozyme unstable and promote its abnormal folding. These misfolded proteins form insoluble amyloid fibrils that accumulate in tissues.
Lysozyme amyloidosis can affect several organs, including .
Glands that produce tears, mucus or saliva, leading to a dry syndrome.
The digestive tract: deposits may cause abdominal pain or transit disorders.
Liver: amyloid deposits can cause liver enlargement (hepatomegaly) and disrupt its functions. Spontaneous liver rupture is a very severe complication of amyloidosis.
Kidneys: Deposits can impair the kidneys' ability to filter blood, leading to excessive protein loss in the urine. This may lead to dialysis.
Cardiac involvement is very rare.
Clinical
Symptoms of lysozyme amyloidosis can vary, but the most common include:
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dry syndrome (dry eyes (keratitis), dry mouth).
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abdominal pain or transit disorders.
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swelling of the legs (oedema).
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internal haemorrhage, particularly due to rupture of the liver dome.
Diagnostic
Diagnosis of lysozyme amyloidosis is based on several tests:
Biopsy: tissue sampling to confirm the presence of amyloid deposits.
Genetic analysis: to identify a mutation in the lysozyme gene.
Imaging tests: CT or MRI scans to assess organ involvement, particularly in the digestive tract.
Evolution
Symptoms appear on average at around 25 years of age. Lysozyme amyloidosis progresses slowly, with a median survival rate of almost 20 years after diagnosis.
Severity is related to digestive hemorrhagic complications such as liver rupture.
Regular clinical and specific biological follow-up at an expert center is essential, particularly in cases of renal failure.
Treatment
Il n’existe pas encore de traitement curatif pour l’amylose du lysozyme, mais certains traitements peuvent aider à gérer les symptômes et à ralentir la progression de la maladie :
- Médicaments pour traiter les complications (comme les diurétiques pour les œdèmes).
- Transplantation d’organe dans les cas graves (par exemple, du foie ou des reins).
Bien que l’amylose à lysozyme soit une maladie rare et complexe, un diagnostic précoce et une prise en charge adaptée dans un centre expert habitué à prendre en charge les amyloses héréditaires rares est conseillé.