Clonal hematopoiesis by SLIT1-mutated hematopoietic stem cells due to a breakdown of the autocrine loop involving Slit1 in acquired aplastic anemia

Clinical and Genetic Analysis of A Father-Son Duo with Monomelic Amyotrophy: Case Report

Monomelic Amyotrophy (MMA) is a rare neurological disorder restricted to one upper limb, predominantly affecting young males with an unknown aetiopathogenesis. We report a familial case of father-son duo affected by MMA. Whole exome sequencing identified genetic variations in SLIT1, RYR3 and ARPP21 involved in axon guidance, calcium homeostasis and regulation of calmodulin signaling respectively. This is the first attempt to define genetic modifiers associated with MMA from India and advocates to extend genetic screening to a larger cohort. Deciphering the functional consequences of variations in these genes will be crucial for unravelling the pathogenesis of MMA.

The GPI-anchored protein CD109 protects hematopoietic progenitor cells from undergoing erythroid differentiation induced by TGF-β

Although a glycosylphosphatidylinositol-anchored protein (GPI-AP) CD109 serves as a TGF-β co-receptor and inhibits TGF-β signaling in keratinocytes, the role of CD109 on hematopoietic stem progenitor cells (HSPCs) remains unknown. We studied the effect of CD109 knockout (KO) or knockdown (KD) on TF-1, a myeloid leukemia cell line that expresses CD109, and primary human HSPCs. CD109-KO or KD TF-1 cells underwent erythroid differentiation in the presence of TGF-β. CD109 was more abundantly expressed in hematopoietic stem cells (HSCs) than in multipotent progenitors and HSPCs of human bone marrow (BM) and cord blood but was not detected in mouse HSCs. Erythroid differentiation was induced by TGF-β to a greater extent in CD109-KD cord blood or iPS cell-derived megakaryocyte-erythrocyte progenitor cells (MEPs) than in wild-type MEPs. When we analyzed the phenotype of peripheral blood MEPs of patients with paroxysmal nocturnal hemoglobinuria who had both GPI(+) and GPI(-) CD34⁺ cells, the CD36 expression was more evident in CD109^- MEPs than CD109⁺ MEPs. In summary, CD109 suppresses TGF-β signaling in HSPCs, and the lack of CD109 may increase the sensitivity of PIGA-mutated HSPCs to TGF-β, thus leading to the preferential commitment of erythroid progenitor cells to mature red blood cells in immune-mediated BM failure.

Hematopoietic stem progenitor cells lacking HLA differ from those lacking GPI-anchored proteins in the hierarchical stage and sensitivity to immune attack in patients with acquired aplastic anemia

To characterize glycosylphosphatidylinositol-anchored protein-deficient (GPI[-]) and HLA-class I allele-lacking (HLA[-]) hematopoietic stem progenitor cells (HSPCs) in acquired aplastic anemia (AA), we studied the peripheral blood (PB) of 56 AA patients in remission who possessed both (n = 13, Group A) or either GPI(-) (n = 34, Group B) and HLA(-) (n = 9, Group C) cell populations. Seventy-seven percent (10/13) of Group A had HLA(-) cells in all lineages of PB cells, including platelets, while only 23% (3/13) had GPI(-) cells in all lineages, and the median percentage of HLA(-) granulocytes in the total granulocytes (21.2%) was significantly higher than that of GPI(-) granulocytes (0.28%, P < 0.05). The greater lineage diversity in HLA(-) cells than in GPI(-) cells was also seen when Group B and Group C were compared. Longitudinal studies of seven patients in Group A showed a gradual decrease in the percentage of HLA(-) granulocytes, with a reciprocal increase in the GPI(-) granulocytes in four patients responding to cyclosporine (CsA) and an increase in the HLA(-) granulocytes with a stable or declining GPI(-) granulocytes in three patients in sustained remission off CsA therapy. These findings suggest that HLA(-) HSPCs differ from GPI(-) HSPCs in the hierarchical stage and sensitivity to immune attack in AA.