Single-Lineage Bone Marrow Failure Driven By 2 Novel PI3KCD Mutations

Five genetic mutation on PI3KCD are known so far to cause the Activated-Phosphoinositide-3-kinaseδ-Syndrome (APDS) a Primary Immune-Deficiency characterized by lymphopenia/hypogammaglobulinemia, respiratory infections, bronchiectasias, gut/pulmonary infiltrates, splenomegaly, autoimmunity and predisposition to malignancies. We report 2 patients carrying 2 novel mutation of PI3KCD gene presenting with a singlelineage bone marrow failure.

Case1: A9-months-old girl with splenomegaly,steroid-responsive autoimmune haemolytic anemia and immune thrombocytopenia,severe persistant neutropenia due to marrow myeloid precursors aplasiaresistant to multiple-agents immunosuppression,recurrent life-threatening infections was referred to our Unit. No myeloid precursors at any stage of maturation were found in the bone marrow aspiration. Growth of both homologous and heterologous myeloid progenitor cells was hampered by patient's marrow plasma.Most common causes of congenital neutropenias were excluded. Sirolimus partially and transiently normalized neutrophil count but after yet another life-threatening sepsis neutropenia relapsed. NGS analysis showed the presence of a novel mutation of PI3KCD gene (H273Y) affecting the enzyme's catalytic domain. She then received analpha-beta-CD19-depleted haplo-identical SCT from her mother (infused18.6x10⁶/kgCD34+,2x10⁴/kgAlpha/beta-T-cells) conditioned withATG-Fludarabine-Melphalan.Neutrophils and platelets recoveredat d+26and+10 respectively.Mixed-chimerismpersistedduring post-transplant andneutropenia relapsed on day +177 when full recipient chimerismwas documented witnessing for rejection.She then underwent anotherhaplo-SCTfrom the mother conditioned with Fludarabine-Melphalan-Campath(infused3x10⁶/kgCD34+, 1.5x10⁵/kgAlfa/beta-T-cells).Neutrophil and platelets recovered at d+18 and +13, respectively.Neither toxicity nor GvHD occurred after both transplants.

Case 2:

A 1 year-old girl presented with Pure Red Cell Aplasia (PRCA) associated with AHIA. No erythroid precursors were seen in the marrow and progenitor colony studies showed that the patient's plasma had an inhibitory effect on the growth of both homologous and control erythroid progenitors. At presentation she also had worsening seizures due to into acute disseminated encephalomyelitis that promptly recovered after few doses of intra-venous immunoglobulins. PRCA/AIHA subsided to combination therapy with Rituximab and Sirolimus and after 2 years of complete remission new episodes of seizures appeared requiring a change of the anti-comitial treatment which by interfering with Sirolimus serum levels caused a relapse of anemiathat was successfully rescued by the addition of monthly IVIG administration. Based on the low Ig levels at the onset of the disease, the response to both Sirolimus (suggesting a mTOR pathway involvement) and IVIG, , we performed Sanger PCR on PI3KCD gene and detected the S277M mutation. To confirm the pathogenetic role of this mutation, we studied the expression of AKT protein by Western blot analysis that showed an increased phosphorilation compared to a same age-healthy control.

This report indicates that thesenew PI3KCD mutations may generate a novel APDS clinical phenotype, consisting of severe single-lineage marrow aplasia,and therefore widen the spectrum of diseases underlying single lineage marrow failure in children. Sirolimus and SCT represent valid options for the treatments of the disease.