Myeloid Leukemia

FIP1L1-PDGFRA in Hypereosinophilic Syndrome 177
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Detection of the FIP1L1-PDGFRA Fusion in Idiopathic
Hypereosinophilic Syndrome and Chronic Eosinophilic
Leukemia
Jan Cools, Elizabeth H. Stover, and D. Gary Gilliland
Summary
Idiopathic hypereosinophilic syndrome (HES) and chronic eosinophilic leukemia (CEL) are
related hematological malignancies characterized by sustained, unexplained hypereosinophilia
(>1,500 eosinophils/µL) (1–4). The term CEL is used when there is evidence that the disease is
of clonal origin. We recently identified the FIP1L1-PDGFRA fusion gene in approx 50% of
HES/CEL cases (5). Fusion of FIP1L1 to PDGFRA is the consequence of a deletion on chromosome
4, del(4)(q12q12), with the centromeric breakpoint in FIP1L1 and the telomeric
breakpoint in PDGFRA. The breakpoints in FIP1L1 are diverse (introns 7 to 10), but the
breakpoints in PDGFRA are always in exon 12 (encoding the juxtamembrane region). because
the chromosomal deletion is only 800 kb in size, it remains undetected with standard cytogenetics.
In agreement with this, most patients with HES/CEL present with a normal karyotype.
Here we describe three different techniques to detect the presence of the FIP1L1-PDGFRA
fusion gene in peripheral blood or bone marrow cells.
Key Words: Eosinophilia; fusion gene; kinase; imatinib; detection.
1. Introduction
The presence of the FIP1L1-PDGFRA fusion gene can be detected in blood
or bone marrow from patients with hypereosinophilia at three different levels:
the chromosome level, the DNA level, and the RNA level (Fig. 1) (5,6). The
FIP1L1-PDGFRA fusion transcript can be detected by reverse transcriptase
polymerase chain reaction (RT-PCR), which is by far the easiest and most sensitive
detection method. Alternatively, the FIP1L1-PDGFRA fusion gene can
be detected and cloned at the DNA level by long-distance inverse PCR (LDI-
PCR), which also allows sequencing of the exact breakpoints within FIP1L1
and PDGFRA. The chromosomal deletion del(4)(q12q12), associated with the
From: Methods in Molecular Medicine, Vol. 125: Myeloid Leukemia: Methods and Protocols
Edited by: H. Iland, M. Hertzberg, and P. Marlton © Humana Press Inc., Totowa, NJ
177