Chronic Granulomatous Disease and Myelodysplastic Syndrome in a Patient with a Novel Mutation in CYBB.

Chronic Granulomatous Disease (CGD) is an inborn error of immunity characterized by impaired phagocyte function, recurrent fungal and bacterial infections and granuloma formation in multiple organs. Pediatric myelodysplastic Syndrome (MDS) is a rare hematological stem cell disease that leads to an ineffective hematopoiesis with variable risk of evolution to acute leukemias. Both disorders are rare and have distinct pathophysiologic mechanisms, with no known association. A 7-month-old boy presenting with recurrent infections and anemia at age 2 months underwent immunological, hematological and genetic investigation that culminated in the diagnosis of both CGD and MDS. Next generation sequencing was performed and identified a silent variant predicted as of Uncertain Significance, located in the splicing site at the end of exon 5 in CYBB. CYBB variants account for at least two thirds of CGD cases, but no previous descriptions of this variant were found in ClinVar or The Human Gene Mutation Database (HGMD) databases. We were able to demonstrate an exon 5 skipping on the proband's cDNA, which strongly suggests the disruption of the NADPH oxidase complex, abrogating the formation of reactive oxygen species from neutrophils. Moreover, erythroid cell lineage could be also affected by NADPH oxidase complex damages. Further investigation is needed to evaluate the potential effect of CYBB gene alterations in hematopoiesis, as well as in MDS and CGD association.

TET2 expression level and 5-hydroxymethylcytosine are decreased in refractory cytopenia of childhood.

Myelodysplastic syndromes (MDS) are myeloid malignancies characterized by ineffective hematopoiesis, dysplasia, peripheral cytopenia and increased risk of progression to acute myeloid leukemia. Refractory cytopenia of childhood (RCC) is the most common subtype of pediatric MDS and has overlapping clinical features with viral infections and autoimmune disorders. Mutations in TET2 gene are found in about 20-25% of adult MDS and are associated with a decrease in 5-hydroxymethylcytosine (5-hmC) content. TET2 deregulation and its malignant potential were reported in adult but not in pediatric MDS. We evaluated the gene expression and the presence of mutations in TET2 gene in 19 patients with RCC. TET2 expression level was correlated with 5-hmC amount in DNA and possible regulatory epigenetic mechanisms. One out of 19 pediatric patients with RCC was a carrier of a TET2 mutation. TET2 expression and 5-hmC levels were decreased in patients when compared to a disease-free group. Lower expression was not associated to the presence of mutation or with the status of promoter methylation, but a significant correlation with microRNA-22 expression was found. These findings suggested that TET2 downregulation and low levels of 5-hmC are inversely related to miR-22 expression. The existence of a regulatory loop between microRNA-22 and TET2 may play a role in MDS pathogenesis.