IGJ and SPATS2L immunohistochemistry sensitively and specifically identify BCR::ABL1+ and BCR::ABL1-like B-acute lymphoblastic leukaemia.

Therapeutic management and prognostication for patients with B-acute lymphoblastic leukaemia (B-ALL) require appropriate disease subclassification. BCR::ABL1-like B-ALL is unique in that it is defined by a gene expression profile similar to BCR::ABL1+ B-ALL rather than a unifying recurrent translocation. Current molecular/cytogenetic techniques to identify this subtype are expensive, not widely accessible, have long turnaround times and/or require an adequate liquid biopsy. We have studied a total of 118 B-ALL cases from three institutions in two laboratories to identify surrogates for BCR::ABL1+/like B-ALL. We report that immunoglobulin joining chain (IGJ) and spermatogenesis associated serine-rich 2-like (SPATS2L) immunohistochemistry (IHC) sensitively and specifically identify BCR::ABL1+/like B-ALL. IGJ IHC positivity has a sensitivity of 83%, a specificity of 95%, a positive predictive value (PPV) of 89% and a negative predictive value (NPV) of 90%. SPATS2L staining has similar sensitivity and NPV but lower specificity (85%) and PPV (70%). The presence of either IGJ or SPATS2L staining augments the sensitivity (93%) and NPV (95%). While these findings would need to be validated in larger studies, they suggest that IGJ and/or SPATS2L IHC may be utilized in identifying BCR::ABL1-like B-ALL or in selecting B-ALL cases for confirmatory molecular/genetic testing, particularly in resource-limited settings.

Mucin 4 protein is expressed in B-acute lymphoblastic leukemia and is restricted to BCR::ABL1-positive and BCR::ABL-like subtypes.

Mucin 4 (MUC4) is a transmembrane mucin that, like most mucins, is not expressed in normal hematopoietic cells, but little is known about its expression in malignant hematopoiesis. B-acute lymphoblastic leukemia (B-ALL) consists of genetically distinct disease subtypes with similarities and differences in gene expression most frequently studied at the mRNA level, which is less amenable to widespread routine clinical use. Here, we demonstrate using immunohistochemistry (IHC) that MUC4 protein is expressed in less than 10% of B-ALL, with expression restricted to BCR::ABL1+ and BCR::ABL1-like (CRLF2 rearranged) subtypes of B-ALL (4/13, 31%). None (0/36, 0%) of the remaining B-ALL subtypes expressed MUC4. We compare clinical and pathologic features of MUC4+ and MUC4- BCR::ABL1+/like cases and most significantly report a possible shorter time to relapse for MUC4+ BCR::ABL1 B-ALL that would need to be validated in larger studies. In conclusion, MUC4 is a specific, albeit insensitive, marker for these high-risk subtypes of B-ALL. We propose that MUC4 IHC may be used diagnostically to rapidly identify these B-ALL subtypes, particularly in resource-limited settings or when an aspirate sample is not available for ancillary genetic studies.

A Novel Homozygous Missense Mutation in the YARS Gene: Expanding the Phenotype of YARS Multisystem Disease.

Aminoacyl-tRNA synthetases (ARSs) are crucial enzymes for protein translation. Mutations in genes encoding ARSs are associated with human disease. Tyrosyl-tRNA synthetase is encoded by YARS which is ubiquitously expressed and implicated in an autosomal dominant form of Charcot-Marie-Tooth and autosomal recessive YARS-related multisystem disease. We report on a former 34-week gestational age male who presented at 2 months of age with failure to thrive (FTT) and cholestatic hepatitis. He was subsequently diagnosed with hyperinsulinemic hypoglycemia with a negative congenital hyperinsulinism gene panel and F-DOPA positron-emission tomography (PET) scan that did not demonstrate a focal lesion. Autopsy findings were notable for overall normal pancreatic islet size and morphology. Trio whole exome sequencing identified a novel homozygous variant of uncertain significance in YARS (c.611A > C, p.Tyr204Cys) with each parent a carrier for the YARS variant. Euglycemia was maintained with diazoxide (max dose, 18 mg/kg/day), and enteral dextrose via gastrostomy tube (G-Tube). During his prolonged hospitalization, the patient developed progressive liver disease, exocrine pancreatic insufficiency, acute renal failure, recurrent infections, ichthyosis, hematologic concerns, hypotonia, and global developmental delay. Such multisystem features have been previously reported in association with pathogenic YARS mutations. Although hypoglycemia has been associated with pathogenic YARS mutations, this report provides more conclusive data that a YARS variant can cause hyperinsulinemic hypoglycemia. This case expands the allelic and clinical heterogeneity of YARS-related disease. In addition, YARS-related disease should be considered in the differential of hyperinsulinemic hypoglycemia associated with multisystem disease.