What causes ttp blood disorder

Overview

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening blood disorder that, if left untreated, can be fatal in more than 90% of cases. It is characterized by the formation of widespread microthrombi (tiny blood clots) in the small blood vessels (microvasculature) of the body. These clots consume platelets, leading to a low platelet count (thrombocytopenia) and can also cause red blood cells to break down prematurely (hemolytic anemia) as they squeeze through narrowed vessels. The blockage of these small vessels can lead to reduced blood flow and damage to vital organs, including the brain, kidneys, and heart.

What Causes TTP?

The underlying cause of TTP is a severe deficiency in the activity of an enzyme called ADAMTS13. This enzyme plays a critical role in the blood's clotting process. Specifically, ADAMTS13 is a metalloprotease that cleaves (cuts) large multimers of von Willebrand factor (vWF) into smaller, functional units. Von Willebrand factor is a protein that helps platelets stick together and form clots when a blood vessel is injured.

In a healthy individual, ADAMTS13 constantly regulates the size of vWF multimers. However, when ADAMTS13 activity is significantly reduced (less than 10% of normal activity is typically seen in TTP), large, ultra-large vWF multimers accumulate in the bloodstream. These ultra-large multimers are highly reactive and cause platelets to spontaneously clump together, forming microthrombi. These microthrombi then lodge in small blood vessels, leading to the characteristic symptoms of TTP.

Types of TTP and Their Causes

TTP can be broadly categorized into two main types, based on its cause:

1. Acquired TTP (Immune-mediated TTP - iTTP)

This is the most common form of TTP, accounting for approximately 90% of all cases. Acquired TTP develops when the body's immune system mistakenly attacks the ADAMTS13 enzyme. This autoimmune response leads to the production of antibodies (autoantibodies) that bind to and inhibit the function of ADAMTS13, or sometimes they cause it to be cleared from the circulation more rapidly. The exact trigger for this autoimmune response is often unknown, but it can sometimes be associated with:

• Infections (viral or bacterial)
• Pregnancy and childbirth
• Certain medications (e.g., ticlopidine, clopidogrel, quinine, some chemotherapies)
• Malignancies (cancers)
• Autoimmune diseases (e.g., lupus)
• Pancreatitis

In many cases, no specific trigger can be identified, and the TTP is considered idiopathic (of unknown cause).

2. Hereditary TTP (hTTP)

Also known as Upshaw-Schulman syndrome, hereditary TTP is a much rarer condition, accounting for about 10% of TTP cases. It is a genetic disorder caused by mutations in the ADAMTS13 gene. Individuals with hTTP inherit two faulty copies of the gene (one from each parent), resulting in a congenital deficiency of the ADAMTS13 enzyme. Unlike acquired TTP, the body does not produce antibodies against ADAMTS13; rather, it simply produces very little or no functional enzyme from birth. Symptoms of hereditary TTP may appear in infancy, childhood, or adulthood, and can be triggered by factors such as infections, pregnancy, or certain medications.

Symptoms and Diagnosis

The symptoms of TTP can vary widely and may develop suddenly or gradually. Common symptoms include:

• Thrombocytopenia (low platelet count): leading to easy bruising, nosebleeds, bleeding gums, and petechiae (tiny red or purple spots under the skin).
• Microangiopathic hemolytic anemia (MAHA): characterized by fatigue, paleness, shortness of breath, and jaundice, due to red blood cells being destroyed as they pass through damaged blood vessels.
• Neurological abnormalities: such as confusion, seizures, stroke-like symptoms, headaches, and changes in consciousness.
• Kidney problems: ranging from mild impairment to severe kidney failure.
• Abdominal pain, nausea, and vomiting.
• Fever.

Diagnosis of TTP relies on a combination of clinical symptoms, blood tests, and specific enzyme assays. Key diagnostic findings include severe thrombocytopenia, evidence of MAHA (e.g., elevated LDH, low haptoglobin, presence of schistocytes in blood smear), and critically low ADAMTS13 activity (<10%). Testing for ADAMTS13 inhibitor antibodies can help differentiate between acquired and hereditary forms.

Treatment

Treatment for TTP is a medical emergency. The primary treatment for acquired TTP is plasma exchange (plasmapheresis), a procedure where the patient's plasma is removed and replaced with donor plasma. This process helps to remove the autoantibodies and ultra-large vWF multimers from the blood, while also replenishing the deficient ADAMTS13 enzyme. Corticosteroids and rituximab (a monoclonal antibody) are also commonly used to suppress the immune system and reduce antibody production. For hereditary TTP, regular plasma infusions to provide the missing ADAMTS13 enzyme may be necessary.