BCOR and BCORL1 Mutations In Pediatric Acute Myeloid Leukemia

In pediatric acute myeloid leukemia (AML) current survival rates are approximately 70%, but further improvements are required to improve disease outcome. Prognosis is correlated to early response to treatment and genetic aberrations (Creutzig et al, 2012). In approximately 20% no cytogenetic aberrations can be identified. In some of these cases repetitive aberrations, such as NPM1 mutations or cryptic translocations including NUP98-translocations (Hollink, 2011 and De Rooij, 2013) have been found. Recently, mutations in BCOR and BCORL1, both located on the X-chromosome, were found in adult AML using next generation sequencing. They both are transcriptional co-repressors, although with distinct binding targets (Tiacci, Heamatologica, 2012), and are thought to represent a novel mechanism of leukemogenesis. Somatic inactivating BCOR mutations were identified in 4% of adult cytogenetically normal (CN-) AML patients, predominantly located in exon 4, but also in other exons (Grossmann et al, 2011). Of interest, germline BCOR mutations cause the X-linked oculo-facio-cardio-dental genetic syndrome, which may occur due to its function as a co-repressor of the BCL6 gene. Somatic inactivating BCORL1mutations were found in 6% of adult AML patients (Li et al, 2011); all mutations were located in exon 4. Their exact role in AML and the targets of their co-repressive transcriptional activity has not been elucidated as yet (Tiacci, Haematologica, 2012).

We screened newly diagnosed pediatric AML patients for the presence of BCOR and BCORL1 mutations using direct sequencing of the complete coding sequence of both genes starting with a cohort of 86 patients including all cytogenetic subgroups patients, and later expanding this with an additional 146 patients for BCORL1screening of exon 4. This cohort was enriched for samples from CN-AML patients (56% and 21% respectively). Samples were obtained from the Dutch Childhood Oncology Group (DCOG; The Hague, The Netherlands), the AML-BFM-SG; Hannover, Germany and Prague, Czech Republic, and the Hôpital Robert Debré (Paris, France).

A single BCOR mutation was found in 1 patient only with CN-AML. The mutation, p.A854T, was located in exon 4. The patient was a 4 year old boy with a FAB M1, WBC 354 x 10⁹/L, who is alive 45 months after diagnosis. In addition, only 1 patient carried a BCORL1 mutation. The mutation, located in exon 4, p.G158X, caused a premature stop-codon. The male patient was diagnosed with secondary AML, aged 17 years, with normal cytogenetics and a WBC of 9.4 x 10⁹/L, FAB M1, and died 3 months after diagnosis. Multiple recurrent SNPs were observed for both BCOR (rs5917933: 7/86 pts (91.9%); rs6520618: 15/86 (17.4%); rs144606152: 6/86 (7.0%)) and BCORL1 (rs4830173: 232/232 (100%); rs5932715: 36/232 (15.5%)), all in exon 4. No relation could be found between the presence of SNPs and disease outcome.

BCOR and BCORL1 mutations occur in less than 1% of pediatric AML patients. These data provide further evidence for the differences in genetic background between pediatric and adult AML. Separate next-generation studies should be performed to elucidate the genetic background of pediatric CN-AML.

This project was funded by KIKA, project number 64, entitled: Aberrant signal transduction profiling in pediatric AML.

No relevant conflicts of interest to declare.