Poikiloderma with neutropenia: beginning at the end

Hypogammaglobulinemia in a Child with Clericuzio-Type Poikiloderma with Neutropenia

Introduction: Poikiloderma with neutropenia (PN) is a rare autosomal recessive hereditary disease caused by biallelic mutations of the USB1 gene. It is characterized by poikiloderma, chronic noncyclic neutropenia, and recurrent sinopulmonary infections with bronchiectasis. Here we report a case with homozygous c.531delA mutation in USB1 gene. Case: An 15-month-old boy was admitted to our clinic with skin hyperpigmentation, growth retardation, and recurrent lower respiratory tract infections. The medical history revealed that he was hospitalized 6 times due to pneumonia since the age of 3 months. His physical examination showed facial dysmorphism with triangular face, depressed nasal bridge, and frontal bossing. He also had poikiloderma in the whole body. Skin biopsy was performed and showed only hyperkeratosis. His weight and height were below the 3 percentile. He is the first child of his consangenius parents. In the laboratuary findings; he has mild neutropenia (1,100/mm3), hypogammaglobulinemia (serum IgG: 351 mg/dL, IgA: 17 mg/dL, IgM: 20 mg/dL) and, peripheral lymphocyte subset analysis was normal. Neutropenia was also observed in previous examinations (980-560-840/mm3). Immunoglobulin replacement therapy and antibiotic prophylaxis were started. Exome sequence analysis showed the presence of known homozygous variant (c.351delA) in USB1 gene. Conclusion: Poikiloderma with neutropenia mainly affects the myeloid lineage. Unlike other patients in the literature, we observed hypogammaglobulinemia in addition to neutropenia in our patient. This case illustrated that it is important to monitor serum immunoglobulin levels in symptomatic patients with recurrent infections.

A zebrafish model of Poikiloderma with Neutropenia recapitulates the human syndrome hallmarks and traces back neutropenia to the myeloid progenitor

Poikiloderma with Neutropenia (PN) is an autosomal recessive genodermatosis characterized by early-onset poikiloderma, pachyonychia, hyperkeratosis, bone anomalies and neutropenia, predisposing to myelodysplasia. The causative C16orf57/USB1 gene encodes a conserved phosphodiesterase that regulates the stability of spliceosomal U6-RNA. The involvement of USB1 in splicing has not yet allowed to unveil the pathogenesis of PN and how the gene defects impact on skin and bone tissues besides than on the haematological compartment. We established a zebrafish model of PN using a morpholino-knockdown approach with two different splicing morpholinos. Both usb1-depleted embryos displayed developmental abnormalities recapitulating the signs of the human syndrome. Besides the pigmentation and osteochondral defects, usb1-knockdown caused defects in circulation, manifested by a reduced number of circulating cells. The overall morphant phenotype was also obtained by co-injecting sub-phenotypic dosages of the two morpholinos and could be rescued by human USB1 RNA. Integrated in situ and real-time expression analyses of stage-specific markers highlighted defects of primitive haematopoiesis and traced back the dramatic reduction in neutrophil myeloperoxidase to the myeloid progenitors showing down-regulated pu.1 expression. Our vertebrate model of PN demonstrates the intrinsic requirement of usb1 in haematopoiesis and highlights PN as a disorder of myeloid progenitors associated with bone marrow dysfunction.