IDH1 and IDH2 gene mutations in South African patients with cytogenetically-normal Acute Myeloid Leukaemia.

Walton, Ashleigh Helen
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Introduction: Mutations in isocitrate dehydrogenase (IDH) 1 and 2 genes have recently been found in Acute Myeloid Leukaemia (AML) and may represent a novel class of mutations with distinct clinical and biological characteristics. They occur more frequently with normal karyotype AML and NPM1 mutations, and may confer a mutation-specific prognostic impact. The frequency of IDH1 and IDH2 mutations has not yet been established in South Africa. Materials and Methods: Samples from 70 cytogenetically-normal paediatric (n=9) and adult (n=61) AML patients were analyzed for IDH1R132, IDH2R140 and IDH2R172 mutations with singleplex polymerase chain reaction (PCR) and direct sequencing. IDH1R132 mutations were further investigated with a mutation-specific, multiplex PCR and agarose gel electrophoresis (AGE). The concurrence of IDH mutations with two common AML gene mutations, NPM1 and FLT3-ITD, was also determined using a multiplex PCR and capillary electrophoresis (CE) assay for NPM1 and FLT3-ITD mutations, followed by a separate singleplex PCR and AGE method for FLT3-ITD and a mutation-specific, multiplex real-time qualitative PCR (qPCR) for NPM1. Results: IDH1R132 mutations were detected in 5 (8.2%) adult patients and 1 (11.1%) paediatric patient. In adults, IDH2R140 and IDH2R172 mutations were detected in 4 (6.6%) patients and 1 (1.6%) patient, respectively. No paediatric patient had IDH2 mutations. IDH1 and IDH2 mutations were heterozygous and mutually exclusive. Concurrent mutations in NPM1 and FLT3-ITD were also detected in patients with mutated IDH1R132 and IDH2R140 but not in the patient with the IDH2R172 mutation. One sample showed discordant results between the singleplex PCR and sequencing method and the mutation-specific, multiplex IDH1R132 PCR. The multiplex PCR and CE assay for NPM1 and FLT3-ITD mutations was more accurate than the separate mutation-specific, multiplex real-time qPCR for NPM1 mutations and the singleplex PCR and AGE method for FLT3-ITDs. For each of these, one discordant result was seen between these techniques. Conclusion: Overall, 16.4% of adult and 11.1% of paediatric cytogenetically-normal AML patients had IDH gene mutations. Multiplex PCR and CE is the preferred method in testing for NPM1 and FLT3-ITD mutations. Although the role of IDH mutations in AML is currently unknown, the mutation-specific, multiplex IDH1R132 PCR offers a suitable and faster alternative to sequencing should these markers be used diagnostically in the future.