Pelger-Huët anomaly: a critical review of the literature

The dynamic nuclear envelope: resilience in health and dysfunction in disease

The canonical appearance of the nucleus depends on constant adaptation and remodeling of the nuclear envelope in response to changing biomechanical forces and metabolic demands. Dynamic events at the nuclear envelope play a vital role in supporting key nuclear functions as well as conferring plasticity to this organelle. Moreover, imbalance of these dynamic processes is emerging as a central feature of disease etiology. This review focuses on recent advances that shed light on the myriad events at the nuclear envelope that contribute to resilience and flexibility in nuclear architecture.

Immature Neutrophils Released in Acute Inflammation Exhibit Efficient Migration despite Incomplete Segmentation of the Nucleus

Acute inflammation recruits neutrophils with a band-shaped nucleus to the circulation. This neutrophil population was recently shown to have superior antibacterial capacity. Early recruitment of banded neutrophils to an infection site will likely improve the outcome of the immune response, yet it critically depends on efficient migration. However, the current dogma states that the segmentation of the mature neutrophil nucleus has evolved to favor migration through narrow pores as found between endothelial cells and in the interstitium. Therefore, we hypothesized that banded neutrophils migrate less efficiently than neutrophils with segmented nuclei, whereas recently described neutrophils with hypersegmented nuclei would in turn migrate more efficiently. Acute inflammation was evoked in a human model of experimental endotoxemia to recruit neutrophil subsets with different nuclear segmentation to the circulation. To simulate migration toward an infection site, migration of the subsets was studied in in vitro models of transendothelial migration or interstitial chemokinesis and chemotaxis. In both models, nuclear segmentation did not increase migration speed. In dense collagen matrices, the speed of the hypersegmented neutrophils was even reduced compared with the banded neutrophils. Fluorescence microscopy suggested that the hypersegmented neutrophils displayed reduced rear release and deposited more membrane vesicles. Vice versa, migration through narrow pores did not induce nuclear segmentation in the neutrophils. In conclusion, like neutrophils with a segmented nucleus, the banded subset exhibited efficient migration through narrow pores. These findings suggest that the nucleus does not preclude the banded subset from reaching an infection site.

A review of blood diseases and cytopenias associated with human parvovirus B19 infection

Parvovirus B19 is a single-stranded DNA virus which preferentially targets the erythroblast resulting in red cell aplasia, which is temporary in immunocompetent persons. Since the discovery of B19 virus in 1975, a wide variety of blood diseases and cytopenias affecting several blood cell lineages have been documented during or following B19 infection. These include cytopenias affecting the erythroid, megakaryoblastoid, myeloid and lymphoid lineages, as well as a variety of bicytopenias, pancytopenia, bone marrow necrosis / fat embolism syndrome, myelodysplastic syndrome, leucoerythroblastopenia, and hemophagocytic lymphohistiocytosis. B19 infection may also complicate and precede the course of acute leukemia, the significance of which remains to be determined. This review describes the current state of knowledge of the abnormalities of individual blood cell lineages encountered during parvovirus B19 infection, over the almost 40 years since its discovery, and reveals some very interesting themes, which improve our understanding of the pathogenesis of B19 infection with particular reference to the bone marrow.

The prognostic utility of degenerative left shifts in dogs

BACKGROUND

A degenerative left shift (DLS) in dogs is reported to be a poor prognostic indicator, but no studies have been reported to verify this claim.

HYPOTHESIS/OBJECTIVES

To characterize the canine population affected by DLS and to determine if the presence and severity of the DLS are associated with increased risk of euthanasia or death.

ANIMALS

Three-hundred and nineteen dogs with DLS (cases) and 918 dogs without DLS (controls) presented to the University of California, Davis Veterinary Medical Teaching Hospital between April 1, 1995 and April 1, 2010.

METHODS

Retrospective case-control study. All cases had a CBC performed within 24 hours of presentation that showed an immature neutrophil count higher than the mature neutrophil count. Controls were matched by year of presentation and primary diagnosis. Survival analysis was used to determine the risk of death or euthanasia associated with DLS and other potential predictors.

RESULTS

Half of cases versus 76% of controls were alive at discharge. Median in-hospital survival time was 7 days for cases and 13 days for controls. DLS was a significant predictor of death or euthanasia in both univariate and multivariate analysis (hazard ratio, HR, 1.9; 95% CI 1.54-2.34).

CONCLUSIONS AND CLINICAL IMPORTANCE

DLS in dogs is associated with an increased risk of death or euthanasia. This finding, however, varies with disease diagnosis and should be interpreted in light of the individual patient.

Nuclear mechanics in disease

Over the past two decades, the biomechanical properties of cells have emerged as key players in a broad range of cellular functions, including migration, proliferation, and differentiation. Although much of the attention has focused on the cytoskeletal networks and the cell's microenvironment, relatively little is known about the contribution of the cell nucleus. Here, we present an overview of the structural elements that determine the physical properties of the nucleus and discuss how changes in the expression of nuclear components or mutations in nuclear proteins can not only affect nuclear mechanics but also modulate cytoskeletal organization and diverse cellular functions. These findings illustrate that the nucleus is tightly integrated into the surrounding cellular structure. Consequently, changes in nuclear structure and composition are highly relevant to normal development and physiology and can contribute to many human diseases, such as muscular dystrophy, dilated cardiomyopathy, (premature) aging, and cancer.

A neonate with the Pelger-Huët anomaly, cleft lip and palate, and agenesis of the corpus callosum, with a chromosomal microdeletion involving 1q41 to 1q42.12

We observed a neonate with cleft lip and palate, 13 sets of ribs, agenesis of the corpus callosum, slightly small penis, hypoglycemia, and what initially appeared to be a marked leukocyte 'left shift' on complete blood count, but which was actually a Pelger-Huët anomaly. A chromosomal microdeletion was identified at1q41-42.12.

Understanding and recognizing the Pelger-Huët anomaly

The Pelger-Huët anomaly (PHA) is a recognized morphologic variant affecting all granulocytes but is most evident in polymorphonuclear neutrophils (PMNs). PHA is caused by a decreased amount of the lamin B receptor (LBR). Recognition of PHA morphologic features serves as a marker for mutations in the LBR gene. This review summarizes the history of PHA and the current knowledge of the functions of the LBR. Guidance is given for distinguishing PHA from other hematologic disorders in which granulocytes may show similar changes. Recognition of PHA in the laboratory should prompt communication to the patient's physician about the possible clinical significance of this finding and the recommended screening for the anomaly in other family members by CBC and review of a peripheral blood smear.

Reduced lymphocyte longevity and homeostatic proliferation in lamin B receptor-deficient mice results in profound and progressive lymphopenia

The lamin B receptor (LBR) is a highly unusual inner nuclear membrane protein with multiple functions. Reduced levels are associated with decreased neutrophil lobularity, whereas complete absence of LBR results in severe skeletal dysplasia and in utero/perinatal lethality. We describe a mouse pedigree, Lym3, with normal bone marrow and thymic development but profound and progressive lymphopenia particularly within the T cell compartment. This defect arises from a point mutation within the Lbr gene with only trace mutant protein detectable in homozygotes, albeit sufficient for normal development. Reduced T cell homeostatic proliferative potential and life span in vivo were found to contribute to lymphopenia. To investigate the role of LBR in gene silencing in hematopoietic cells, we examined gene expression in wild-type and mutant lymph node CD8 T cells and bone marrow neutrophils. Although LBR deficiency had a very mild impact on gene expression overall, for common genes differentially expressed in both LBR-deficient CD8 T cells and neutrophils, gene upregulation prevailed, supporting a role for LBR in their suppression. In summary, this study demonstrates that LBR deficiency affects not only nuclear architecture but also proliferation, cell viability, and gene expression of hematopoietic cells.

Congenital Pelger-Huët anomaly in a Danish/Swedish Farmdog: case report

A 13 year old Danish/Swedish Farmdog from Denmark was evaluated in a veterinary clinic in Warsaw, Poland for evaluation of an orthopedic problem. Radiographs revealed spondylosis and degenerative vertebral disease, which responded to treatment with anti-inflammatory medications. A predominance of hyposegmented neutrophils and eosinophils containing condensed chromatin and normal cytoplasm were identified on a routine CBC. Follow-up blood film evaluations over the course of 12 months confirmed that the hyposegmented granulocytes persisted. The majority of neutrophils contained Grade 2 nuclei (slightly indented), and the mean nuclear score varied from 1.9 to 2.3. Pelger-Huët anomaly (PHA), presumably congenital, was diagnosed based on persistent hyposegmented granulocytes in the absence of an underlying cause for acquired PHA; genetically related dogs were unavailable for testing to confirm vertical transmission. To the authors' knowledge this is the first report of PHA in a Danish/Swedish Farmdog.

Pseudo-Pelger-Huët anomaly induced by medications: a clinicopathologic study in comparison with myelodysplastic syndrome-related pseudo-Pelger-Huët anomaly

Pseudo-Pelger-Huët anomaly (PPHA) has been documented in association with transplant medications and other drugs. This iatrogenic neutrophilic dysplasia is reversible with cessation or adjustment of medications but is frequently confused with myelodysplastic syndrome (MDS) based on the conventional concept that PPHA is a marker for dysplasia. We investigated the clinicopathologic features in iatrogenic PPHA and compared them with MDS-related PPHA. The 13 cases studied included 5 bone marrow/stem cell transplantations, 3 solid organ transplantations, 1 autoimmune disease, 3 chronic lymphocytic leukemias, and 1 breast carcinoma. For 12 cases, there was follow-up evaluation, and all demonstrated at least transient normalization of neutrophilic segmentation. All 9 cases of MDS demonstrated at least 2 of the following pathologic abnormalities on bone marrow biopsy: hypercellularity (8/9), morphologic dysplasia (8/9), clonal cytogenetic abnormality (7/9), and increased blasts (3/9), whereas these abnormalities were typically absent in iatrogenic PPHA. Iatrogenic PPHA displayed a higher proportion of circulating PPHA cells than in MDS (mean, 47.4%; SD, 31.6% vs mean, 12.3%; SD, 9.8; P < .01). A diagnostic algorithm is proposed in which isolated PPHA is indicative of transient or benign PPHA unless proven otherwise.

Malformation syndromes caused by disorders of cholesterol synthesis

Cholesterol homeostasis is critical for normal growth and development. In addition to being a major membrane lipid, cholesterol has multiple biological functions. These roles include being a precursor molecule for the synthesis of steroid hormones, neuroactive steroids, oxysterols, and bile acids. Cholesterol is also essential for the proper maturation and signaling of hedgehog proteins, and thus cholesterol is critical for embryonic development. After birth, most tissues can obtain cholesterol from either endogenous synthesis or exogenous dietary sources, but prior to birth, the human fetal tissues are dependent on endogenous synthesis. Due to the blood-brain barrier, brain tissue cannot utilize dietary or peripherally produced cholesterol. Generally, inborn errors of cholesterol synthesis lead to both a deficiency of cholesterol and increased levels of potentially bioactive or toxic precursor sterols. Over the past couple of decades, a number of human malformation syndromes have been shown to be due to inborn errors of cholesterol synthesis. Herein, we will review clinical and basic science aspects of Smith-Lemli-Opitz syndrome, desmosterolosis, lathosterolosis, HEM dysplasia, X-linked dominant chondrodysplasia punctata, Congenital Hemidysplasia with Ichthyosiform erythroderma and Limb Defects Syndrome, sterol-C-4 methyloxidase-like deficiency, and Antley-Bixler syndrome.

The danger of "multi-tasking": LBR out of control

The nuclear envelope (NE) is a barrier that separates nuclear from cytoplasmic processes. It is composed of an inner and outer nuclear membrane (INM, ONM), separated by the perinuclear space (PNS). The ONM is contiguous with the endoplasmic reticulum (ER), and thus, the lumen of the NE and that of the ER constitute one compartment. The lamin B receptor (LBR) is a NE protein that has a central structural role as a linker of the INM, the lamina and chromatin, and a less well characterized functional role as a sterol reductase. In a recent study, we reported that the forced expression of mutant variants of LBR in some cell types induces a separation of the INM from the outer nuclear envelope concomitantly with a separation of ER membranes, whereas in other cells no separation is observed. In this extra view, we speculate about the mechanism that leads to this fundamental disruption of NE and ER structure. Our observations furthermore raise the question to what extent LBR contributes to the establishment or maintenance of the ER and PNS luminal compartment, and how a single mutant protein can so drastically interfere with its regular organization.

Lamin B receptor: multi-tasking at the nuclear envelope

Lamin B receptor (LBR) is an integral membrane protein of the interphase nuclear envelope (NE). The N-terminal end resides in the nucleoplasm, binding to lamin B and heterochromatin, with the interactions disrupted during mitosis. The C-terminal end resides within the inner nuclear membrane, retreating with the ER away from condensing chromosomes during mitotic NE breakdown. Some of these properties are interpretable in terms of our current structural knowledge of LBR, but many of the structural features remain unknown. LBR apparently has an evolutionary history which brought together at least two ancient conserved structural domains (i.e., Tudor and sterol reductase). This convergence may have occurred with the emergence of the chordates and echinoderms. It is not clear what survival values have maintained LBR structure during evolution. But it seems likely that roles in post-mitotic nuclear reformation, interphase NE growth and compartmentalization of nuclear architecture might have provided some evolutionary advantage to preservation of the LBR gene.