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Also known as: HES/Leukemia; 4q12 (CHIC2) deletion; PDGFRA-FIP1L1 gene rearrangement; FIP1-like-1/platelet-derived growth factor alpha
Formal name: FIP1L1-PDGFRA Fusion by FISH or RT-PCR

The Test Sample

What is being tested?

FIP1L1-PDGFRA is an abnormal fusion gene sequence that causes excessive growth of eosinophils, a type of white blood cell. It is a rare cause of hypereosinophilia (HE) and hypereosinophilic syndrome (HES). This test detects the FIP1L1-PDGFRA gene sequence.

While some genetic abnormalities are inherited from our parents, they can also come from changes that occur to genes or chromosomes after a person is born. These are called somatic mutations, which can occur through exposure to various environmental factors (e.g., radiation, certain chemicals), but more often for unknown reasons.

The FIP1LI-PDGFRA gene sequence is one of those genetic changes acquired after birth. It occurs when a mutation on chromosome 4 causes deletion of approximately 800 nucleotides, or DNA building blocks, which normally separate the FIP1L1 and PDGFRA genes. Because of this deletion, the two genes are brought together, producing a new fusion gene. Other types of mutations can also lead to abnormalities of the PDGFRA gene, but this deletion is the most common.

Normally, the PDGFRA gene provides instructions for making a protein that controls processes like cell growth and division. When the mutation occurs and the FIP1L1-PDGFRA fusion gene is present, the gene sequence still provides instructions for making that protein, but the protein that results is different because it is always activated and continues to send signals for growth and division. With constant signals for growth, eosinophils (and sometimes other blood cells) can grow out of control, causing hypereosinophilia (HE) and hypereosinophilic syndrome (HES), which can be fatal if not treated promptly.

Hypereosinophilia (HE) and Hypereosinophilic syndrome (HES)

Eosinophils are a type of white blood cell that are involved in allergic reactions and immune responses to certain parasites. The number of eosinophils in the blood may be elevated with these conditions. Hypereosinophilia is the prolonged overproduction of eosinophils. As increasing numbers of eosinophils infiltrate and inflame tissues, HES develops. HES is a condition caused when infiltrative eosinophils affect and damage a variety of organs, including the heart, lungs and the nervous system.

Common symptoms include chest pain and shortness of breath, if the heart is involved. People with HES may also have anemia or excessive clotting (hypercoaguability), stroke, blurred vision or slurred speech. Other symptoms may involve the gastrointestinal system or the skin. Sometimes, there may be no symptoms, when tissue or organ damage is less severe.

There are a number of causes of HE and HES besides genetic abnormalities. Allergic diseases are the most common cause in the developed world. Parasitic diseases, certain cancers, autoimmune disorders, skin disease, inflammatory bowel syndrome, and Addison disease can also cause HES. If an individual has HES and a health practitioner has ruled out these secondary causes, genetic testing can determine if FIP1L1-PDGFRA or other genetic abnormality is the underlying cause.

Only 0.4% of people with persistently high numbers of eosinophils carry the FIP1L1-PDGFRA gene. It is most common in individuals between 20 and 50 years old. Although it is a rare cause of HE and HES, it is important to identify it because HE/HES with FIP1L1-PDGFRA can be fatal if not treated but is effectively treated with the drug imatinib.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm or a bone marrow sample is collected using a bone marrow aspiration and/or biopsy procedure.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.