Yaddanapudi Ravindranath

Poikiloderma with neutropenia, Clericuzio type (PN; OMIM #604173), is a rare autosomal recessive genodermatosis caused by biallelic loss-of-function variants in U6 snRNA Biogenesis 1 (USB1), with approximately 100 molecularly confirmed cases. Beyond the defining post-inflammatory poikiloderma and non-cyclic neutropenia, affected individuals show recurrent sinopulmonary infection, impaired wound healing, tendon contractures, and primary gonadal failure in males. USB1 is a 2H-superfamily 3′ to 5′ exoribonuclease that removes oligoadenylate tails added by Poly(A) polymerase associated protein 5 (PAPD5) and PAPD7; its loss destabilizes guide-strand microRNAs and blocks the emergence of CD45+ hematopoietic progenitors. Splicing is not measurably disturbed in patient cells, so the earlier splicing-centered account requires revision. Drawing on previously unpublished endocrine, neurologic and imaging data from two affected brothers, we develop a candidate model in which the microRNA lesion reaches cyclic nucleotide signaling by two routes: de-repression of phosphodiesterase E3B (PDE3B) after loss of miR-142-5p, and loss of a perinuclear and Golgi cyclic AMP compartment after coordinate reduction in A-kinase anchoring protein 6 (AKAP6) and PDE4D interacting protein (PDE4DIP). We state where the model is supported, where it conflicts with published effects, and what would refute it, arguing for compartment-restricted dysregulation rather than global deficiency. PAPD5/7 inhibition, leading to repression of PDE3B, is closest to the causal lesion, but its on-target neurotoxicity makes it an experimental tool rather than a candidate drug.

Summary: A heterozygous Kruppel‐like factor 1 (KLF1) E325K mutation causes a severe form of congenital dyserythropoietic anaemia (CDA), designated CDA‐IV (Online Mendelian Inheritence in Man, OMIM 613673), a rare disease with only 15 cases known. In addition to haemolytic anaemia, manifest often at birth, four of seven (57%) of 46,XY children with KLF1 E325K mutation exhibit a range of dysmorphic external genitalia including 46,XY complete sex reversal (2/7 or 28.5%). No genital abnormalities were reported in a boy with double heterozygous KLF1 null mutations, suggesting that the KLF1 E325K variant causes, in addition to its negative impacts on erythroid differentiation, disruptions in male sex differentiation. Our studies suggest a role for a cooperative effect of concurrent ‘non‐pathogenic’ polymorphisms in multiple genes associated with disorders of sex differentiation (DSD), notably fibroblast growth factor 9 ( FGF9 ), whose expression was decreased in the gonads and peripheral blood in the case described here. We propose that the combined loss of FGF9 and CD44 (a target for CDA‐IV KLF1) resulted FGF9 signalling loss and likely caused 46,XY sex reversal. Our studies also suggest that whole‐blood gene expression studies in the proband/parent triad may provide critical clues in evaluating children with DSD, the cause of which remains undiagnosed in many cases.

X‐linked sideroblastic anemia (XLSA) is categorized as hypochromic microcytic anemia. In 3 children with XLSA, we observed prominent elliptocytosis, and red cell band 3 content histograms were similar to those found in hereditary elliptocytosis, thus validating Cooley's descriptions in 1945.

Summary: Poikiloderma with neutropenia (PN) Clericuzio type (OMIM #604173) is a rare disease with areas of skin hyper‐ and hypopigmentation caused by biallelic USB1 variants. The current study was spurred by poor healing of a perianal tear wound in one affected child homozygous for c.266‐1G>A (p.E90Sfster8) mutation, from a family reported previously. Treatment with G‐CSF/CSF3 or GM‐CSF/CSF2 transiently increased neutrophil/monocytes count with no effect on wound healing. Analysis of peripheral blood revealed a lack of non‐classical (CD14^+/−CD16⁺) monocytes, associated with a systemic inflammatory cytokine profile, in the two affected brothers. Importantly, despite normal expression of cognate receptors, monocytes from PN patients did not respond to M‐CSF or IL‐34 in vitro, as determined by cytokine secretion or CD16 expression. RNAseq of monocytes showed 293 differentially expressed genes, including significant downregulation of GATA2, AKAP6 and PDE4DIP that are associated with leucocyte differentiation and cyclic adenosine monophosphate (cAMP) signalling. Notably, the plasma cAMP was significantly low in the PN patients. Our study revealed a novel association of PN with a lack of non‐classical monocyte population. The defects in monocyte plasticity may contribute to disease manifestations in PN and a defective cAMP signalling may be the primary effect of the splicing errors caused by USB1 mutation.

Congenital Dyserythropoietic Anemia Type IV (CDA-IV) is still an emerging new disease with approximately 10 cases reported over the past three decades. CDA-IV is known to be caused by a specific mutation in exon 3 of KLF1, an erythroid transcription factor KLF1 with substitution of glutamic acid with lysine at residue 325 (KLF1 E325K). Because of the rarity of this disorder the presenting features are incompletely defined; especially the non-erythroid comorbidities. Here we report a new case, a male child, presenting with fetal hydrops and dysmorphic external genitalia.

Children with Down syndrome (DS) are at an increased risk of developing transient abnormal myelopoiesis (TAM) and acute leukemia. Aberrant expression of CD56 has been observed on myeloid leukemic blasts in DS patients. In general, CD56 expression in acute myeloid leukemia (AML) is considered a promoter of leukemogenesis. We did a retrospective flow cytometric study to investigate mature myelomonocytic cell CD56 expression patterns in TAM, non-TAM, and leukemia cases with DS. Flow cytometric analysis showed that granulocyte and monocyte aberrant/dysplastic CD56 expression is an inherent characteristic of most DS patients irrespective of the presence of TAM or leukemia. Increased CD56 expression in monocyte and granulocyte populations in DS could be multifactorial; greater expression of RUNX1 secondary to the gene dose effect of trisomy 21 along with the maturational state of the cells are the potential contributors. Unlike AML seen in non-DS patients, CD56 overexpression in DS AML cases does not appear to play a role in leukemogenesis.

Non Rhabdomyosarcoma Soft Tissue Sarcomas (NRSTS) are rare in the pediatric age group, accounting for 1-7% of all pediatric tumors. Leiomyosarcoma, a subtype of NRSTS, is exceedingly rare in pediatric population. Due to the rarity of this condition, management is extrapolated from other common NRSTS which involves surgery, chemotherapy and radiation. Chemotherapy is not very effective in management of pediatric leiomyosarcoma and molecular information may help guide targeted therapies. We describe a patient with a FGFR1-TACC1 gene rearrangement which, based on other models, predicts for sensitivity to FGFR inhibitors.

Monocyte subset analysis by flow cytometry has been shown to be a useful diagnostic tool in chronic myelomonocytic leukemia in adults. An increase in the classical monocyte fraction (CD14++/CD16-) greater than 94.0% of total monocytes is considered highly sensitive and specific in distinguishing CMML from other myeloproliferative disorders. In a pilot study of juvenile myelomonocytic leukemia cases, we noted that CD14++/CD16- monocyte fraction was >95% in de novo JMML with somatic PTPN11 mutations but normal in those with monosomy 7 or Noonan syndrome. Monocyte subgroup profiling by itself is not diagnostic of JMML but may distinguish molecular subgroups within JMML.