NPM1 Insertion Mutation
The NPM1 gene encodes a phosphoprotein that is commonly expressed and highly conserved. The NPM1 protein is localized in the nucleolus, and is used as a molecular chaperone to shuttle between the nucleus and the cytoplasm. An overall insertion of four base pairs causes a frameshift that leads to the aberrant localization of the NPM1 protein in the cytoplasm. Several different mutations have been observed for NPM1, however they are all insertions of four base pairs overall and result in the same frameshift.
Research has shown that patients positive for the NPM1 insertion mutations (NPM1m) who test negative for FLT3-ITD have a trend toward better event-free survival (EFS) and overall survival (OS). Patients who test positive for FLT3-ITD show no significant difference in EFS or OS, despite the presence of absence of NPM1m.
DNA is extracted from peripheral blood or bone marrow samples and the NPM1 transcript is amplified by polymerase chain reaction (PCR). Patient samples are run in duplicate with the appropriate positive and negative controls. A PCR reaction, using primers flanking exon 12 is used to detect four nucleotide insertions near the C-terminus region of the gene. A labeled probe is attached to the forward primer for fluorescence detection by capillary gel electrophoresis. Analysis of the PCR product reveals a molecular weight band four base pairs higher than the normal NPM1 wild-type band when an insertion mutation is present. The wild-type band is present in both normal and mutation patient samples, and is used as the endogenous control.
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Questions pertaining to testing may be addressed to the Molecular Oncology Laboratory at 206-667-2592