The enigma of KMT2A gene in hematological disorders

Abstract Introduction/Objective Presence of distinct MLL rearrangements is an independent dismal prognostic factor. Rearrangements of the histone lysine [K]- MethylTransferase 2A gene (KMT2A) on chromosome 11q23, formerly known as the mixed-lineage leukemia (MLL) gene, are found in 10% and 5% of adult and children with acute leukemia respectively. Chromosome 11 breakpoints are typically localized to band 11q23.3, frequently altering the proto- oncogene KMT2A/MLL whereas partner chromosomes involved in translocation may vary. More than 80 different gene partners involved in this fusion have been described, although the majority of leukemias results from 6 common partner genes. KMT2A gene rearrangement are associated with poor prognosis in both Lymphoid and Myeloid leukemia. Methods/Case Report A retrospective study conducted in Cytogenetic laboratory of The Indus hospital, Karachi. All karyotype cases (age 1-60 year) with chromosome 11 aberrations were included from October 2020 to December 2022. Karyotype and FISH performed using G-banding and break a part probe for MLL respectively. Results (if a Case Study enter NA) Total of 923 cases received for karyotyping out of which 32(3.4%) cases were reported for 11q23 abnormalities. The median age was 5 (1.25-12.5) years, majority 15 (47%) were 1-10 years, 9(28%) were >10 years and 7(22%) were <1 years. M:F ratio was 1.9:1. B-ALL were 19(59.4%), AML 8(25%), and 5 (15.6%) were others. FISH performed in 23(72%) cases, 21 (91%) showed concordance with karyotype. The t(9;11) was the commonest 7(22%), followed by t(4;11) and (1;11). Chromosome 9 was the most common partner identified in B-ALL. Loss of 11q23 observed in 3 (13%) cases. Conclusion The findings underscore the heterogeneity of partner chromosomes involved in KMT2A gene rearrangements and emphasize the importance of employing both FISH and karyotyping for comprehensive detection. The high concordance rate between the two methods supports their complementary roles in clinical diagnostics. Understanding the specific translocations and partner chromosomes associated with MLL gene rearrangements contributes valuable insights for prognostication and targeted therapeutic strategies in acute leukemia. FISH and karyotype showed 91% concordance to detect this aberration.