Transient Myeloproliferative Disorder as the Presenting Feature for Mosaic Trisomy 21

Trisomy 21 is a common congenital disorder with well documented clinical manifestations, including an increased risk for transient myeloproliferative disorder as a neonate and leukemia in childhood and adolescence. Children with mosaic trisomy 21 can have a similar risk for hematological malignancies. We present a non-dysmorphic neonate, with negative noninvasive prenatal screening of maternal blood for trisomy 21, who came to medical attention because of ruddy skin. He was found to have mild polycythemia, thrombocytopenia and developed peripheral blasts. His clinical presentation was concerning for transient myeloproliferative disorder, which is only seen in trisomy 21 patients. Cytogenetic studies were positive for mosaic trisomy 21.

A 3-D Hydrogel Based System for Hematopoietic Differentiation and its Use in Modeling Down Syndrome Associated Transient Myeloproliferative Disorder

Induced pluripotent stem cells (iPSCs) provide an extraordinary tool for disease modeling owing to their potential to differentiate into the desired cell type. The differentiation of iPSCs is typically performed...

Modeling Transient Myeloproliferative Disorder Using Induced Pluripotent Stem Cells and CRISPR/Cas9 Technology

Down syndrome (DS) is recognized as one of the most important leukemia-predisposing syndromes. Specifically, 1-2% of DS children develop acute myeloid leukemia (AML) prior to age 5. AML in DS children (DS-AML) is characterized by the pathognomonic mutation in the gene encoding the essential hematopoietic transcription factor GATA1, resulting in N-terminally truncated mutant GATA1 (GATA1s). Trisomy 21 and GATA1s together induce a transient myeloproliferative disorder (TMD) exhibiting pre-leukemic characteristics. Approximately thirty percent of these cases progress into DS-AML by acquisition of additional somatic mutations in a step-wise manner. We employed disease modeling in vitro by the use of customizable induced pluripotent stem cells (iPSCs) (7, 8) to generate a TMD model. Isogenic iPSC lines derived from the fibroblasts of a DS patient with trisomy 21 and with disomy 21 were used. We also obtained DS2-iPS10 (iPSCs derived from DS patient fibroblast) from Prof. George Daley, Children's Hospital, Harvard University (Boston, MA). CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)/Cas9 system with the indicated guide sequence (Fig. 1A) was used to introduce clinically relevant GATA1 mutation in both disomic and trisomic iPSC lines. A representative plot of TIDE (Tracking of Indels by Decomposition) analysis showing 98% allelic mutation frequency of a clone with 2 bp deletion at chromosomal level (Fig. 1B) correlated with sequence analysis using Basic Local Sequence Alignment Tool (BLAST) and Sanger sequencing chromatogram (Fig. 1C). This mutation resulted in the disruption of first initiation codon and thus prevented the production of full length GATA1 protein, while allowing the usage of second initiation codon at 84th position to generate GATA1s. GATA1 and GATA1s are not expressed in iPSCs. To determine the expression of GATA1s, we differentiated these mutant iPSC lines into hematopoietic stem cell progenitors (HSPCs) using hematopoietic differentiation kit (StemCell Technologies) following a protocol depicted in Fig. 1D. The HSPCs derived from two distinct clones of trisomic iPSCs showed expression of full-length GATA1 protein and GATA1 mutant HSPCs lacked the expression of full-length GATA1 as expected (Fig. 1E). These HSPCs expressed GATA1s. Given that trisomy 21 promotes hematopoietic differentiation, an increase in the percentage of erythroid, megakaryoid and myeloid population was observed in trisomy 21 HSPCs with full length GATA1 (Fig. 1F, compare bars 1 and 3 in each category). The expression of GATA1s reduced erythroid lineage cells whereas it augmented megakaryoid and myeloid lineages in both disomy 21 (compare red and blue bars 1 and 2) and trisomy 21 backgrounds (compare bars 3 and 4). HSPCs derived from trisomy 21 iPSCs with GATA1s exhibited more megakaryoid expansion compared to the GATA1s in disomy 21 background (Fig. 1F, compare bars 2 and 4), in agreement with the synergistic function of trisomy 21 and GATA1s in promoting TMD. Transplantation of HSPCs derived from GATA1 mutated trisomic iPSCS into NSG-SGM3 mice showed the presence of human CD45+ cells in peripheral blood at 12 weeks post cell injection (Fig. 1G). In conclusion, we have developed a model system representing TMD, which can be used for step-wise modeling of Down-syndrome AML by introducing additional mutations. Figure 1 Disclosures No relevant conflicts of interest to declare.

Transient Myeloproliferative Disorder: An Update for Neonatal Nurses

Down syndrome (DS) is a well-known genetic disorder that affects 700–1,000 infants per year. One particular comorbidity of DS is transient myeloproliferative disorder (TMD), a disease characterized by leukocytosis with elevated blast counts. Approximately 10 percent of DS infants develop TMD, which usually manifests during the first week of life and can lead to an extended hospitalization in a NICU. In addition to hallmark hematologic findings, other manifestations include jaundice, conjugated hyperbilirubinemia, hepatomegaly, and pericardial or pleural effusions. TMD generally resolves spontaneously in the first three months of life with the provision of timely medical management; however, survivors are at increased risk of developing acute myeloid leukemia (AML). Neonatal nurses need to have knowledge of this disorder to facilitate screening of DS infants and optimize family education and coordination of care.

Chromosome 21 Gain Is Dispensable for Transient Myeloproliferative Disorder (TMD) Development

Transient myeloproliferative disorder (TMD) is a hematopoietic disease, characterized by a clonal proliferation of immature megakaryoblasts in the neonatal period occurring in approximately 10% of newborns with Down syndrome (DS). Rarely, TMD occurs in non-DS newborns but then it is associated with somatic trisomy 21 (tri21). Tri21 together with in-utero gained mutations in the GATA1 gene encoding a myeloid transcription factor are thus considered essential in TMD. Recently, we have identified a TMD with a typical manifestation and course in a newborn without DS/somatic tri21, which admits that tri21 is dispensable for TMD development. To elucidate the alternative TMD pathogenesis, we performed comprehensive genomic/transcriptomic profiling of this TMD case. We utilized high-density SNP array and whole exome and transcriptome sequencing (WES/RNAseq) to detect copy number changes, mutations and fusion genes. We did not find any aberrations on chromosome 21 and any fusion genes. Two focal intronic losses, likely representing benign germline variants, were found on chromosome X. In addition to 6 missense mutations affecting genes without established roles in hematopoietic disorders, we found in-frame deletions in the GATA1 and JAK1 genes. Both mutations are novel. The GATA1 D65_C228del mutation is predicted to result in an internally truncated protein - GATA1aber. Unlike GATA1s (resulting from GATA1 mutations in DS-TMD) which lacks the transactivation domain (TAD) but retains both Zinc fingers (ZF), GATA1aber lacks part of TAD and the N-terminal ZF. Nevertheless, we hypothesize that GATA1aber substitutes the pathogenetic role of GATA1s. The JAK1 gene encodes a non-receptor tyrosine-kinase engaged in the JAK/STAT signaling pathway. The identified mutation results in the loss of phenylalanine 636 (F636del), which is located in the pseudokinase domain and belongs to a conserved amino acid triad (F636-F575-V658) that is believed to mediate a structural switch controlling the JAK1 catalytic activity (Toms, Nat Struct Mol Biol, 2013). JAK1 mutations are implicated in various hematological malignancies including acute megakaryocytic leukemia, and we hypothesize that JAK1 F636del co-operates with GATA1aber on TMD pathogenesis via deregulation of cytokine/growth factor signaling. We cloned the coding sequences of GATA1aber and JAK1 F636del and transfected them into a model cell line in which we confirmed the expression of both in-silico predicted proteins. Their subcellular trafficking was analogous to that of their wild type counterparts; GATA1aber was found in the nucleus and JAK1 F636del in both the nucleus and cytoplasm. Next, we assessed the kinase activity of JAK1 F636del. To distinguish auto- from trans-phosphorylation, we utilized the JAK1 F636del construct harboring an inactivating mutation of an ATP-binding site (K908G). The JAK1 F636del (but not JAK1 F636del + K908G) was autophosphorylated on Y1034/Y1035 and induced STATs phosphorylation both under steady-state conditions and following non-specific stimulation with PMA. However, at all studied time points all phosphorylation levels were lower compared to wild-type JAK1. Moreover, unlike constitutively active JAK1 V658I, JAK1 F636del did not confer IL3-independent growth to the murine B-cell progenitor cell line BAF3. Interestingly, the transforming potential of double-mutated JAK1 (JAK1 V658I + F636del) was enforced compared to JAK1 V658I. These data show that F636del does not lead to constitutive activation, but in the same time it is not functionally neutral. As the impact of F636del on JAK1 function may vary depending on upstream signaling, we are currently assessing JAK1 F636 kinase activity/transforming potential in BAF3 cells stably expressing the IL6 receptor, which (unlike the IL3 receptor) directly activates JAK1 upon ligand binding. In the future, we plan to study the impact of JAK1 F636del on GATA1s induced deregulation of erythroid/megakaryocytic lineage development and to demonstrate "GATA1s-like" function of GATA1aber. To conclude, we identified two novel mutations affecting GATA1 and JAK1 as likely drivers in an alternative tri21-independent TMD pathogenesis. As the pathogenetic role of tri21 has been poorly understood so far, we believe that by clarifying an alternative mechanism of TMD development, we could improve our understanding of this intriguing disease in general. Support: GAUK 86218 Disclosures No relevant conflicts of interest to declare.