Inclusion body myopathy, Paget's disease of the bone and frontotemporal dementia: recurrence of the VCP R155H mutation in an Italian family and implications for genetic counselling

The acronym IBMPFD denotes a syndrome including inclusion body myopathy, Paget's disease of the bone (PDB) and frontotemporal dementia (FTD) as cardinal features, which is caused by missense mutations in the VCP gene. We studied the clinical characteristics and the histopathological features in two siblings and their mother who presented with adult-onset myopathy and presenile, rapidly progressive FTD. One sibling also showed PDB. Light and electron microscopy performed on muscle biopsies demonstrated degenerative changes with inclusion bodies and abnormal aggregates. Mutation analysis of the VCP gene on affected siblings revealed a heterozygous missense mutation (R155H) in a hot spot. This is the first Italian family with multiple individuals diagnosed as having IBMPFD and carrying the recurrent R155H mutation. The implications for genetic counselling were also discussed, with regard to the procedures that may be offered to families suffering from a multisystem disorder with high risk of cognitive decline.

Hypokalemic periodic paralysis in a patient with acquired growth hormone deficiency

CONTEXT

Hypokalemic periodic paralysis (HypoPP) is a rare disorder consisting of sudden episodes of muscle weakness with areflexia involving all four limbs, which spontaneously resolve within several hours or days. Primary HypoPP is genetically determined, while secondary acquired HypoPP has been described in association with thyreotoxycosis, hyperaldosteronism, kidney diseases, diuretics and liquorice abuse, gastrointestinal potassium loss, or cysplatinum therapy.

OBJECTIVE

To report a case of HypoPP associated with GH deficiency.

PATIENT

A 33 yr-old man with hypopituitarism and diabetes insipidus secondary to pituitary stalk-localized sarcoidosis, and documented HypoPP episodes.

CLINICAL PRESENTATION

Neurologic exam outside HypoPP episodes was normal. Needle electromyography was normal without myotonia or other spontaneous electric activity. Muscle biopsy documented a vacuolar myopathy with tubular aggregates. However, genetic analysis ruled out common mutations of the voltage-gated calcium channel observed in primary HypoPP. Common causes of secondary HypoPP were also ruled out. The patient was diagnosed with severe GH deficiency with modest fasting hyperinsulinemia and insulin resistance and started on GH replacement therapy, an alpha-glucosidase inhibitor (acarbose) and a diet low in simple carbohydrates.

CONCLUSIONS

GH replacement therapy, acarbose and a diet low in simple carbohydrates resulted in the complete long-term (>2 yr) remission of HypoPP episodes. This is consistent with the hypothesis that the hyperinsulinemia associated to GH deficiency may trigger HypoPP episodes by increasing Na+/K+ ATPase activity and K+ transport into the intracellular compartment with subsequent hypokalemia.

Phenotypic clustering of lamin A/C mutations in neuromuscular patients

BACKGROUND

Mutations in the LMNA gene, encoding human lamin A/C, have been associated with an increasing number of disorders often involving skeletal and cardiac muscle, but no clear genotype/phenotype correlation could be established to date.

METHODS

We analyzed the LMNA gene in a large cohort of patients mainly affected by neuromuscular or cardiac disease and clustered mutated patients in two groups to unravel possible correlations.

RESULTS

We identified 28 variants, 9 of which reported for the first time. The two groups of patients were characterized by clinical and genetic differences: 1) patients with childhood onset displayed skeletal muscle involvement with predominant scapuloperoneal and facial weakness associated with missense mutations; 2) patients with adult onset mainly showed cardiac disorders or myopathy with limb girdle distribution, often associated with frameshift mutations presumably leading to a truncated protein.

CONCLUSIONS

Our findings, supported by meta-analysis of previous literature, suggest the presence of two different pathogenetic mechanisms: late onset phenotypes may arise through loss of function secondary to haploinsufficiency, while dominant negative or toxic gain of function mechanisms may explain the severity of early phenotypes. This model of patient stratification may help patient management and facilitate future studies aimed at deciphering lamin A/C pathogenesis.

Dominant LMNA mutations can cause combined muscular dystrophy and peripheral neuropathy

The coexistence of neurogenic and myogenic features in scapuloperoneal syndrome is rarely ascribed to a single gene. Defects in the nuclear envelope protein lamin A/C, encoded by the LMNA gene, have been shown to be associated with a variety of disorders affecting mainly the muscular and adipose tissues and, more recently, with autosomal recessive Charcot-Marie-Tooth type 2 neuropathy. This report is about a patient presenting features of myopathy and neuropathy due to a dominant LMNA mutation, suggesting that the peripheral nerve might be affected in primary LMNA myopathy. Our observations further support the marked intrafamilial and interfamilial phenotypic heterogeneity associated with lamin A/C defects.

Schwann cells synthesize alpha7beta1 integrin which is dispensable for peripheral nerve development and myelination

Defects in laminins or laminin receptors are responsible for various neuromuscular disorders, including peripheral neuropathies. Interactions between Schwann cells and their basal lamina are fundamental to peripheral nerve development and successful myelination. Selected laminins are expressed in the endoneurium, and their receptors are developmentally regulated during peripheral nerve formation. Loss-of-function mutations have confirmed the importance and the role of some of these molecules. Here we show for the first time that another laminin receptor, alpha7beta1 integrin, previously described only in neurons, is also expressed in Schwann cells. The expression of alpha7 appears postnatally, such that alpha7beta1 is the last laminin receptor expressed by differentiating Schwann cells. Genetic inactivation of the alpha7 subunit in mice does not affect peripheral nerve formation or the expression of other laminin receptors. Of note, alpha7beta1 is not necessary for basal lamina formation and myelination. Nonetheless, these data taken together with the previous demonstration of impaired axonal regrowth in alpha7-null mice suggest a possible Schwann cell-autonomous role for alpha7 in nerve regeneration.

Autoantibodies to amphiphysin I and amphiphysin II in a patient with sensory-motor neuropathy

A proportion of patients with peripheral neuropathies has circulating autoantibodies directed against neural antigens. In some cases, autoantibodies may play a pathogenic role. We studied a patient with a progressive sensory-motor axonal neuropathy of unknown etiology, looking for circulating autoantibodies against neural antigens and we showed that the patient's serum contained anti-amphiphysin I (AMP I) and amphiphysin II (AMP II) autoantibodies. A sural nerve biopsy revealed an axonal neuropathy. Indirect immunofluorescence experiments with the patient's serum showed a staining of rat axons due to alpha-AMP I autoantibodies and a specific labelling of cytoplasm and Schmidt-Lanterman incisures of Schwann cells due to alpha-AMP II autoantibodies. In conclusion we identified a patient affected by a sensory-motor neuropathy with autoantibodies against both AMP I and AMP II.

Role of integrins in the peripheral nervous system

Integrins, a subgroup of adhesion receptors, are transmembrane glycoproteins that mediate interactions between cytoplasm and the extracellular environment. These interactions influence, among others, events such as cell migration, proliferation, and differentiation. Differential expression of integrins is developmentally regulated in the peripheral nervous system (PNS) and is associated with crucial events in both physiological and pathological processes. Preliminary studies suggest that integrin expression influences neural crest cell migration, axonal outgrowth, and Schwann cell differentiation. Similarly, the abnormal expression of integrins or their ligands, is associated with degenerative, inflammatory, and malignant disorders of the PNS. Finally, integrins participate in the complex interactions that promote repair of the PNS. A better comprehension of the role of integrins in the PNS, their protein interactions and transducing signals is being achieved by selected biochemical and genetic experiments. Here we review a large bias of evidence suggesting the key functions for integrins in the PNS.

Expression of angiopoietin-1 in human glioblastomas regulates tumor-induced angiogenesis: in vivo and in vitro studies

To define a role for the angiopoietin/Tie2 system in astrocytoma angiogenesis, we examined the expression of angiopoietin-1 (Ang1) and angiopoietin-2 (Ang2) in these tumors by immunohistochemistry and in situ hybridization. Furthermore, we studied in vitro the effects elicited by glioblastoma cell-secreted Ang1 or by recombinant Ang1 on functions of endothelial cells (ECs). Our observations of astrocytomas show that a stage-specific induction of angiopoietins occurs and is correlated with angiogenic phases of different intensity. Ang1 expression was found in a few astrocytes scattered in the tumor at all stages of astrocytoma progression. In blood vessels, Ang1 mRNA increased progressively in high-grade glioblastomas, in which the number of vessels was higher than in low-grade tumors. Ang2 was detected in tumor cells and in ECs in high-grade astrocytomas, whereas its expression was negligible in low-grade tumors. Coculture of glioblastoma cell lines producing Ang1 with endothelium demonstrated a key role of this ligand in the control of EC network organization. We found that recombinant Ang1 in vitro induces EC spreading and reorganization of the cell monolayer into cordlike structures. These results suggest that Ang1 directly acts on ECs by modulating cell-cell and cell-matrix associations and promoting the differentiation phase of angiogenesis.

Human IgM anti-GM1 autoantibodies modulate intracellular calcium homeostasis in neuroblastoma cells

Increased titers of IgM anti-GM1 antibodies are present in some patients with Lower Motor Neuron Disease (LMND) or Motor Neuropathy (MN), but their pathogenic role and the mechanism of action are unclear. Previous studies have shown that the B subunit of Cholera Toxin (CT), which binds and crosslinks ganglioside GM1, modulate intracellular calcium in murine neuroblastoma cells via the activation of L-type voltage-dependent calcium channels (VGCC). Therefore, using a fluorimetric approach, we have examined the hypothesis that the pentameric IgM anti-GM1 antibodies, could similarly alter calcium concentration in N18 neuroblastoma cells. Sera with human IgM anti-GM1 antibodies were obtained from 5 patients with LMND and 2 patients with MN. Human IgG anti-GM1, IgM anti-Myelin Associated Glycoprotein (MAG), IgM anti-sulfatide antibodies and lectin peanut agglutinin (PNA), that recognizes specifically the Gal(betal-3)GalNAc epitope, were used as control sera. Direct application of either human IgM anti-GM1 antibodies or the B subunit of CT to N18 neuroblastoma cells induced a sustained influx of manganese ions, as indicated by a quench of the intracellular fura-2 fluorescence. Furthermore, the dihydropyridine L-type channel antagonists completely inhibited the manganese influx, suggesting that it is due to activation of an L-type VGCC. The magnitude of the influx was correlated with antibody titers. None of human IgG anti-GM1, IgM anti-MAG, IgM anti-sulfatide antibodies or PNA induce an ion influx, pointing to the selective participation of the pentameric IgM isotype of anti-GM1 in the modulation of L-type calcium channels opening. Given that L-type calcium channels are present on motor neurons, the modulation of L-type calcium channels by IgM GM1 antisera may have important implications in diseases such as LMND and MN.

Epitope-tagged P(0) glycoprotein causes Charcot-Marie-Tooth-like neuropathy in transgenic mice

In peripheral nerve myelin, the intraperiod line results from compaction of the extracellular space due to homophilic adhesion between extracellular domains (ECD) of the protein zero (P(0)) glycoprotein. Point mutations in this region of P(0) cause human hereditary demyelinating neuropathies such as Charcot-Marie-Tooth. We describe transgenic mice expressing a full-length P(0) modified in the ECD with a myc epitope tag. The presence of the myc sequence caused a dysmyelinating peripheral neuropathy similar to two distinct subtypes of Charcot-Marie-Tooth, with hypomyelination, altered intraperiod lines, and tomacula (thickened myelin). The tagged protein was incorporated into myelin and was associated with the morphological abnormalities. In vivo and in vitro experiments showed that P(0)myc retained partial adhesive function, and suggested that the transgene inhibits P(0)-mediated adhesion in a dominant-negative fashion. These mice suggest new mechanisms underlying both the pathogenesis of P(0) ECD mutants and the normal interactions of P(0) in the myelin sheath.

Laminin receptor alpha6beta4 integrin is highly expressed in ENU-induced glioma in rat

Laminins and their receptors influence neoplastic growth and invasiveness. We recently reported the abnormal expression of a laminin receptor, alpha6beta4 integrin, in human astrocytomas. To further investigate the role of alpha6beta4 in gliomas, we produced an experimental model of glioma in rat by transplacental ethylnitrosourea (ENU) administration. This animal model allowed us to study the timing of alpha6beta4 expression during tumor development and the topography of expression in the tumor and the surrounding tissue. Immunohistochemistry, in situ hybridization, and immunoprecipitation studies demonstrated that alpha6beta4 heterodimer forms in experimental gliomas, and confirmed that alpha6beta4 is expressed diffusely in neoplastic cells and reactive astrocytes, but not in normal glia surrounding the tumors. Interestingly, alpha6beta4 was expressed from the early phases of tumor development, and more highly expressed by cells in the proliferative centers of the tumors. Both neoplastic cells and reactive astrocytes also expressed the glial growth factor (neuregulin) receptors, Erb-B2 and Erb-B3. Finally, alpha6beta4 expression was reduced in a subset of tumor blood vessels. Thus, this study suggests a potential role for alpha6beta4 in the pathogenesis of gliomas. Furthermore, this is the first description of altered integrin expression in experimental gliomas; transplacental ENU-induced gliomas in rat will provide a useful model to study the role of altered adhesion in the pathogenesis of human gliomas.

The role of integrins in immune-mediated diseases of the nervous system

Immune-mediated diseases of the CNS and PNS, such as multiple sclerosis and Guillain-Barré syndrome, respectively, constitute a major cause of transient and permanent neurological disability in the adult. The aetiology and pathogenesis of these disorders are only partially understood. On a cellular level, focal mononuclear-cell infiltration with demyelination and eventual axonal loss is a crucial pathogenetic event that leads to inflammation and subsequent dysfunction. Here, the evidence that integrins, a family of cell adhesion molecules, expressed on neural and immune cells might play a central role in immune cell recruitment to the CNS and PNS, and probably in tissue repair is reviewed. Distinct integrin expression patterns are observed in multiple sclerosis and Guillain-Barré syndrome. Therapeutic targeting of integrins has been very successful in the corresponding animal models and holds promise as a novel treatment strategy to combat human immune-mediated disorders of the nervous system.

Expression of integrins in experimental autoimmune neuritis and Guillain-Barré syndrome

Integrins are a subclass of adhesion molecules that mediate cell-cell and cell-extracellular matrix interactions. Integrins influence transendothelial migration of lymphocytes and monocytes and are suitable targets for experimental immunotherapy. They are critically involved in the pathogenesis of autoimmune neuritis and abnormally expressed in human neuropathies. Also, the role of integrins in myelination, neurite outgrowth, and nerve regeneration suggests that they could be involved in the recovery phase of immune-mediated neuropathies. We investigated by immunohistochemistry the expression of a number of integrin subunits during the course of experimental autoimmune neuritis (EAN). Results were compared with the human immune neuropathy Guillain-Barre syndrome (GBS) and extended in vitro. Inflammation and demyelination in both EAN and GBS induced the down-regulation of beta4 integrin in Schwann cells (SCs), whereas loss of alpha2 was noted only in EAN. When axonal loss was present, SCs displayed alpha5 integrin, in both EAN and GBS. In vitro, basal lamina and inflammatory cytokines modulated the expression of beta4 in SCs, but they did not influence alpha2 and alpha5 expression. Finally, integrins were differentially expressed in blood vessels during EAN. In conclusion, the spatiotemporal changes in integrin expression may be used to characterize, stage, and better understand the pathogenesis and evolution of inflammation during GBS and EAN. This may help to establish useful, novel therapy for immune-mediated neuropathies.

Modulation of the expression of integrins on glial cells during experimental autoimmune encephalomyelitis. A central role for TNF-alpha

Integrins comprise a group of adhesion receptors involved in cell-cell and cell-extracellular matrix interactions. Evidence is accumulating that integrins expressed on mononuclear cells play a central role in the induction of autoimmune diseases of the central nervous system. The effects of integrins on glial cell behavior, myelination, and angiogenesis suggest that they may also have a role in resolving inflammation in the nervous system and in promoting tissue repair. We investigated the temporospatial expression of integrins in the rat central nervous system during the course of experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis. A higher expression of alpha v- and beta 4-integrin subunits in astrocytes and alpha 2 integrin in oligodendrocytes was observed in active lesions of experimental autoimmune encephalomyelitis, in comparison with controls. Proinflammatory cytokines, primarily TNF-alpha, also enhanced alpha v, beta 4, and alpha 2 expression in purified glial cells ex vivo. Furthermore, we observed that the expression of some integrin subunits was modulated in the cerebral vasculature during inflammation. Our results suggest an active role for glial and vascular integrins in the regulation of autoimmune diseases of the central nervous system, opening an avenue for new potential immunotherapies.