Germline MYOF1::WNK4 and VPS25::MYOF1 Chimeras Generated by the Constitutional Translocation t(17;19)(q21;p13) in Two Siblings With Myelodysplastic Syndrome.

BACKGROUND/AIM: Constitutional chromosomal aberrations are rare in hematologic malignancies and their pathogenetic role is mostly poorly understood. We present a comprehensive molecular characterization of a novel constitutional chromosomal translocation found in two siblings - sisters - diagnosed with myelodysplastic syndrome (MDS). MATERIALS AND METHODS: Bone marrow and blood cells from the two patients were examined using G-banding, RNA sequencing, PCR, and Sanger sequencing. RESULTS: We identified a balanced t(17;19)(q21;p13) translocation in both siblings' bone marrow, blood cells, and phytohemagglutinin-stimulated lymphocytes. The translocation generated a MYO1F::WNK4 chimera on the der(19)t(17;19), encoding a chimeric serine/threonine kinase, and a VPS25::MYO1F on the der(17), potentially resulting in an aberrant VPS25 protein. CONCLUSION: The t(17;19)(q21;p13) translocation found in the two sisters probably predisposed them to myelodysplasia. How the MYO1F::WNK4 and/or VPS25::MYO1F chimeras, perhaps especially MYO1F::WNK4 that encodes a chimeric serine/threonine kinase, played a role in MDS pathogenesis, remains incompletely understood.

Acute Lymphoblastic Leukemia With Near-haploid Karyotype and Philadelphia Chromosome.

BACKGROUND/AIM: In precursor B-cell lineage acute lymphoblastic leukemia (BCP-ALL), leukemic cells harbor genetic abnormalities that play an important role in the diagnosis, prognosis, and treatment. A subgroup of BCP-ALL is characterized by the presence of a Philadelphia (Ph) chromosome and a chimeric BCR::ABL1 gene, whereas in another subgroup, leukemic cells exhibit near-haploidy with chromosome number 24-30. This study presents the third documented case of BCP-ALL in which a near haploid clone concurrently displayed a Ph chromosome/BCR::ABL1. CASE REPORT: Bone marrow cells obtained at diagnosis from a 25-year-old man with BCP-ALL were genetically investigated using G-banding, fluorescence in situ hybridization, and array comparative genomic hybridization. Leukemic cells had an abnormal karyotype 28,X,-Y,+6,+10,+18,+21,+ der(22) t(9;22)(q34;q11)[13]/28,idem, del(10)(q24),der(12) t(1;12) (q21;p13)[2]/46,XY[3], retained heterozygosity of the disomic chromosomes 6, 10, 18, and 21, had breakpoints in introns 1 of ABL1 and BCR, and carried a BCR::ABL1 chimera encoding the 190 kDa BCR::ABL1 protein. CONCLUSION: The coexistence of the BCR::ABL1 chimera and near-haploidy in the same cytogenetic clone suggested a possible synergistic role in leukemogenesis, with the former activating signaling pathways and the latter disrupting gene dosage balance.

Genetic characterization of intramuscular myxomas.

Introduction: Intramuscular myxomas are benign tumors that are challenging to diagnose, especially on core needle biopsies. Acquired chromosomal aberrations and pathogenic variants in codon 201 or codon 227 in GNAS complex locus gene (GNAS) have been reported in these tumors. Here we present our genetic findings in a series of 22 intramuscular myxomas. Materials and methods: The tumors were investigated for the presence of acquired chromosomal aberrations using G-banding and karyotyping. Pathogenic variants in codon 201 or codon 227 of GNAS were assessed using direct cycle Sanger sequencing and Ion AmpliSeq Cancer Hotspot Panel v2 methodologies. Results: Eleven tumors carried chromosomal abnormalities. Six tumors had numerical, four had structural, and one had both numerical and structural chromosomal aberrations. Gains of chromosomes 7 and 8 were the most common abnormalities being found in five and four tumors respectively. Pathogenic variants in GNAS were detected in 19 myxomas (86%) with both methodologies. The detected pathogenic variants were p.R201H in nine cases (seven with abnormal and two with normal karyotypes), p.R201C in five cases, all with normal karyotypes, p.R201S in three cases (two with abnormal and one with normal karyotype), p.R201G in one case with a normal karyotype, and p.Q227E in one case with a normal karyotype. Conclusion: Firstly, our data indicate a possible association between chromosomal abnormalities and GNAS pathogenic variants in intramuscular myxomas. Secondly, the presence of the rare pathogenic variants R201S, p.R201G and p.Q227E in 26% (5 out of 19) of myxomas with GNAS pathogenic variants shows that methodologies designed to detect only the common "hotspot" of p.R201C and p.R201H will give false negative results. Finally, a comparison between Ion AmpliSeq Cancer Hotspot Panel v2 and direct cycle Sanger sequencing showed that direct cycle Sanger sequencing provides a quick, reliable, and relatively cheap method to detect GNAS pathogenic variants, matching even the most cutting-edge sequencing methods.

Genetic Characterization of Pediatric Mixed Phenotype Acute Leukemia (MPAL).

BACKGROUND/AIM: Mixed phenotype acute leukemia (MPAL) is a rare hematologic malignancy in which the leukemic cells cannot be assigned to any specific lineage. The lack of well-defined, pathogenetically relevant diagnostic criteria makes the clinical handling of MPAL patients challenging. We herein report the genetic findings in bone marrow cells from two pediatric MPAL patients. PATIENTS AND METHODS: Bone marrow cells were examined using G-banding, array comparative genomic hybridization, RNA sequencing, reverse transcription polymerase chain reaction, Sanger sequencing, and fluorescence in situ hybridization. RESULTS: In the first patient, the genetic analyses revealed structural aberrations of chromosomal bands 8p11, 10p11, 11q21, and 17p11, the chimeras MLLT10::PICALM and PICALM::MLLT10, and imbalances (gains/losses) on chromosomes 2, 4, 8, 13, and 21. A submicroscopic deletion in 21q was also found including the RUNX1 locus. In the second patient, there were structural aberrations of chromosome bands 1p32, 8p11, 12p13, 20p13, and 20q11, the chimeras ETV6::LEXM and NCOA6::ETV6, and imbalances on chromosomes 2, 8, 11, 12, 16, 19, X, and Y. CONCLUSION: The leukemic cells from both MPAL patients carried chromosome aberrations resulting in fusion genes as well as genomic imbalances resulting in gain and losses of many gene loci. The detected fusion genes probably represent the main leukemogenic events, although the gains and losses are also likely to play a role in leukemogenesis.

Acute Undifferentiated Leukemia With a Balanced t(5;10)(q35;p12) Resulting in Fusion of HNRNPH1 With MLLT10.

BACKGROUND/AIM: Acute undifferentiated leukemia (AUL) is leukemia which does not express lineage-specific antigens. Such cases are rare, accounting for 2.7% of all acute leukemia. The reported genetic information of AULs is limited to less than 100 cases with abnormal karyotypes and a few cases carrying chimeric genes or point mutation of a gene. We herein present the genetic findings and clinical features of a case of AUL. CASE REPORT: Bone marrow cells obtained at diagnosis from a 31-year-old patient with AUL were genetically investigated. G-Banding karyotyping revealed an abnormal karyotype: 45,X,-Y,t(5;10)(q35;p12),del(12)(p13)[12]/46,XY[5]. Array comparative genomic hybridization examination confirmed the del(12)(p13) seen by G-banding but also detected additional losses from 1q, 17q, Xp, and Xq corresponding to the deletion of approximately 150 genes from these five chromosome arms. RNA sequencing detected six HNRNPH1::MLLT10 and four MLLT10::HNRNPH1 chimeric transcripts, later confirmed by reverse-transcription polymerase chain reaction together with Sanger sequencing. Fluorescence in situ hybridization analysis showed the presence of HNRNPH1::MLLT10 and MLLT10::HNRNPH1 chimeric genes. CONCLUSION: To the best of our knowledge, this is the first AUL in which a balanced t(5;10)(q35;p12) leading to fusion of HNRNPH1 with MLLT10 has been detected. The relative leukemogenic importance of the chimeras and gene losses cannot be reliably assessed, but both mechanisms were probably important in the development of AUL.