The gene fusions BCR‐ABL1, TCF3‐PBX1, and ETV6‐RUNX1 are recurrent in B‐cell acute lymphoblastic leukemia (B‐ALL) and are found with low frequency in coexistence with CRLF2 (cytokine receptor‐like factor 2) rearrangements and overexpression. There is limited information regarding the CRLF2 abnormalities and dominant‐negative IKZF1 isoforms associated with surrogate markers of Jak2, ABL, and Ras signaling pathways. To assess this, we evaluated 24 Mexican children with B‐ALL positive for recurrent gene fusions at diagnosis. We found CRLF2 rearrangements and/or overexpression, dominant‐negative IKZF1 isoforms, and surrogate phosphorylated markers of signaling pathways coexisting with recurrent gene fusions. All the BCR‐ABL1 patients expressed CRLF2 and were positive for pCrkl (ABL); most of them were also positive for pStat5 (Jak2/Stat5) and negative for pErk (Ras). TCF3‐PBX1 patients with CRLF2 abnormalities were positive for pStat5, most of them were also positive for pCrkl, and two patients were also positive for pErk. One patient with ETV6‐RUNX1 and intracellular CRLF2 protein expressed pCrkl. In some cases, the activated signaling pathways were reverted in vitro by specific inhibitors. We further analyzed a TCF3‐PBX1 patient at relapse, identifying a clone with the recurrent gene fusion, P2RY8‐CRLF2, rearrangement, and phosphorylation of the three surrogate markers that we studied. These results agree with the previous reports regarding resistance to treatment observed in patients with recurrent gene fusions and coexisting CRLF2 gene abnormalities. A marker phosphorylation signature was identified in BCR‐ABL1 and TCF3‐PBX1 patients. To obtain useful information for the assessment of treatment in B‐ALL patients with recurrent gene fusions, we suggest that they should be evaluated at diagnosis for CRLF2 gene abnormalities and dominant‐negative IKZF1 isoforms, in addition to the analyses of activation and inhibition of signaling pathways.

Nonmosaic trisomy involving 19p13.3p13.2 is a very uncommon abnormality. At present, only 12 cases with this genetic condition have been reported in the literature. However, the size of the trisomic fragment is heterogeneous and thus, the clinical spectrum is variable. Herein, we report the clinical and cytogenetic characterization of a 5-year-old boy with nonmosaic trisomy 19p13.3p13.2 (7.38 Mb), generated by a derivative Y chromosome resulting from a de novo unbalanced translocation t(Y;19)(q12;p13.2). We demonstrated the integrity of the euchromatic regions in the abnormal Y chromosome to confirm the pure trisomy 19p. Our patient shares some clinical features described in other reported patients with pure trisomy 19p, such as craniofacial anomalies, developmental delay, and heart defects. Different to previous reports, our case exhibits frontal pachygyria and polymicrogyria. These additional features contribute to further delineate the clinical spectrum of trisomy 19p13.3p13.2.

<b><i>Introduction:</i></b> The pure interstitial trisomy 11q11q23.2 is an uncommon genomic disorder associated with nonrecurrent intrachromosomal duplications. The phenotype is characterized by intellectual disability and craniofacial abnormalities. Given their uncommonness, a comprehensive genotype-phenotype correlation has not fully been defined. <b><i>Case Presentation:</i></b> We report the clinical and cytogenomic characterization of a 5-year-old boy with intellectual disability, psychomotor retardation, craniofacial dysmorphism, genital anomalies, and pure interstitial trisomy 11q arising from a nonrecurrent 11q13.1q22.3 intrachromosomal duplication in a high-mosaic state (&#x3e;80%). The duplicated chromosome was characterized by cytogenetics, multicolor banding FISH, and SNP array. We demonstrated the wide mosaic distribution of the 11q duplication by interphase FISH in tissues from different embryonic germ layers. The duplication involves a copy number gain of 45.3 Mb containing 22 dosage-sensitive genes. We confirmed the overexpression of dosage-sensitive genes along the duplicated region using RT-qPCR. <b><i>Discussion:</i></b> Only 8 patients have been described. Our patient shares clinical features with previous reports but differs from them by the presence of genital anomalies. We provide a detailed clinical review and an accurate genotype-phenotype correlation and propose <i>PC</i>, <i>NDUFV1</i>, <i>FGF3</i>, <i>FGF4</i>, and <i>DHCR7</i> as dosage-sensitive genes with a possible role in the clinical spectrum of our patient; however, expression changes of <i>FGF3/4</i> were not detected since they must be regulated in a spatiotemporal way. This patient contributes to the accurate description of the pure interstitial trisomy 11q. Future reports could continue to delineate the description, considering the relationship between the chromosome segment and the genes involved.