Clinical utility gene card for: poikiloderma with neutropenia

Clinical, genetic aspects and molecular pathogenesis of osteopetrosis

Osteopetrosis ("marble bone", ICD-10-78.2) includes a group of hereditary bone disorders distinguished by clinical variability and genetic heterogeneity. The name "osteopetrosis" comes from the Greek language: 'osteo' means 'bone' and 'petrosis' means 'stone', which characterizes the main feature of the disease: increased bone density caused by imbalances in bone formation and remodeling, leading to structural changes in bone tissue, predisposition to fractures, skeletal deformities. These defects, in turn, affect other important organs and tissues, especially bone marrow and the nervous system. The disease can be autosomal recessive, autosomal dominant, X-linked or sporadic. Autosomal dominant osteopetrosis has an incidence of 1 in 20,000 newborns and autosomal recessive one has 1 in 250,000. To date, 23 genes have been described, structural changes in which lead to the development of osteopetrosis. Clinical symptoms in osteopetrosis vary greatly in their presentation and severity. The mildest skeletal abnormalities are observed in adulthood and occur in the autosomal dominant form of osteopetrosis. Severe forms, being autosomal recessive and manifesting in early childhood, are characterized by fractures, mental retardation, skin lesions, immune system disorders, renal tubular acidosis. Clinical examination and review of radiographs, bone biopsy and genetic testing provide the bases for clinical diagnosis. The early and accurate detection and treatment of the disease are important to prevent hematologic abnormalities and disease progression to irreversible neurologic consequences. Most patients die within the first decade due to secondary infections, bone marrow suppression and/or bleeding. This article summarizes the current state of the art in this field, including clinical and genetic aspects, and the molecular pathogenesis of the osteopetrosis.

Incomplete splicing of neutrophil-specific genes affects neutrophil development in a zebrafish model of poikiloderma with neutropenia

Poikiloderma with neutropenia (PN) is a rare inherited disorder characterized by poikiloderma, facial dysmorphism, pachyonychia, short stature and neutropenia. The molecular testing of PN patients has identified mutations in the C16orf57 gene, which encodes a protein referred to as USB1 (U Six Biogenesis 1). In this study, we developed a zebrafish model of PN by the microinjection of morpholino antisense oligos to suppress usb1 gene function. Severe morphological defects, including a bent tail, thin yolk extension and reduced body length, were predominant in the Usb1-suppressed embryos (morphants). We also observed significantly decreased number of neutrophils in the morphants by Sudan Black staining. Interestingly, the splicing of genes involved in neutrophil differentiation and development, such as mpx, ncf1, ela3l and npsn, was aberrant in the morphants. However, the splicing of haematopoietic precursors and erythroid-specific genes was unaltered. Importantly, the neutrophil defects were almost completely rescued by co-injection of ela3l mRNA, the most markedly affected gene in the morphants. Our study demonstrated a possible role of USB1 in modulating the tissue-specific gene splicing that eventually leads to the impaired development of neutrophils. This zebrafish model could serve as a valuable tool to investigate the causative role of USB1 in PN pathogenesis.

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.

Poikiloderma with neutropenia: genotype-ethnic origin correlation, expanding phenotype and literature review

Poikiloderma with neutropenia (PN), is a rare genodermatosis associated with patognomic features of poikiloderma and permanent neutropenia. Three common recurrent mutations of related gene, USB1, were considered to be associated with three different ethnic origins. The most common recurrent mutation, c.531delA, has been detected in seven Caucasian patients in the literature. In this paper, we present review of all patients from the literature and report two additional patients of Turkish ancestry with the diagnosis of PN. The diagnosis of these two PN patients were made clinically and confirmed by molecular analysis which detected the most common recurrent mutation, c.531delA. Genotype-ethnic origin correlation hypothesis, therefore, has been strengthened with this result. Short stature in PN, is a common finding, which until now has never been treated with growth hormone (GH). One of our patients is the first patient with attempted treatment of short stature via GH administration. Finally, both of our patients had high-pitched voice and vocal cord nodules which might be considered as additional clinical findings not associated with PN before.