Mastocytosis (NORD)

Mastocytosis, or clonal mast cell disease, is a rare disorder that leads to increased numbers of incorrectly functioning mast cells.

Mast cells are a kind of white blood cell that have many roles in the immune system, including allergic reactions.

There are two main categories of mastocytosis. In cutaneous mastocytosis, the mast cells accumulate only in the skin.

In systemic mastocytosis, mast cells also accumulate in other tissues, like the liver, spleen, lymph nodes, gastrointestinal tract, and, most commonly, bone marrow.

Generally, the signs and symptoms of mastocytosis are similar to an allergic reaction. They can range between categories and from mild to life-threatening.

Some examples are pain, flushing, malaise, headaches, memory and concentration difficulties, stomach aches, production of more than the usual amount of gastric juices, abdominal discomfort, nausea, bloating or diarrhea, and anaphylaxis which is a severe allergic reaction that can be deadly.

Now, within each main category of mastocytosis, there are additional forms. Their distinction can be based on more specific signs and symptoms.

For example, in the most common form of cutaneous mastocytosis, lesions appear on the skin’s surface as brownish, flat or elevated spots.

They may be surrounded by Darier’s signs, which are areas of skin that become red and itchy when scratched or rubbed.

In the rarest form, lesions aren’t present but the skin is rougher and thicker. Itching and blistering may also occur in individuals who are less than one year old.

Some skin changes may be present in systemic mastocytosis, but these forms also involve dysfunction in other tissues.

Blood cell production in the bone marrow may decrease and bones may soften and weaken. In addition to liver dysfunction, swelling or enlargement of the liver, spleen or lymph nodes may occur.

In aggressive systemic mastocytosis, liver function may be lost and in advanced mastocytosis, other blood disorders such as leukemias can form.

Normally developing mast cells are found in the bone marrow. And as they mature, they leave the bone marrow and sit in tissues around the body.

There they have an important role in activating the immune system to defend the body against a threat, such as an insect sting, alcohol, or physical or emotional stress.

When a threat triggers a response, mast cells become activated and release a large amount of chemicals, like histamine or leukotrienes, into the surrounding tissue. These chemicals lead to a specific immune system response called an allergic reaction.

Typically, mastocytosis is caused by changes or mutations in the KIT gene, also called mast/stem cell growth factor receptor, and the most common mutation is D816V.