No Mutation in the SLC2A3 Gene in Cohorts of GLUT1 Deficiency Syndrome-Like Patients Negative for SLC2A1 and in Patients with AHC Negative for ATP1A3

The facilitative glucose transporter-1 (GLUT1) deficiency or de Vivo syndrome is a rare neuropediatric disorder characterized by drug-resistant epilepsy, acquired microcephaly, delayed psychomotor development, intermittent ataxia, and other paroxysmal neurological disorders due to the presence of dominant mutations in the SLC2A1 gene. Alternating hemiplegia of childhood (AHC) is another rare neuropediatric disorder characterized by episodes of hemiplegia developing during the first 1.5 years of life. Before the recent finding of the gene ATP1A3 as the major cause of AHC, a heterozygous missense mutation in the SLC2A1 gene encoding GLUT1 was described in one child with atypical AHC, suggesting some clinical overlap between AHC and GLUT1 deficiency syndrome (GLUT1DS1). Half of patients with symptoms evocative of GLUT1DS1 with hypoglycorrhachia and up to 25 % of patients with AHC remain molecularly undiagnosed. We investigated whether mutations in SLC2A3 encoding GLUT3, another glucose transporter predominant in the neuronal cell, may account the case of a cohort of 75 SLC2A1 negative GLUTDS1-like patients and seven patients with AHC who were negative for ATP1A3 and SLC2A1 mutations. Automated Sanger sequencing and qPCR analyses failed to detect any mutation of SLC2A3 in the patients analyzed, excluding this gene as frequently mutated in patients with GLUT1DS1 like or AHC.

[Congenital myasthenic syndromes: difficulties in the diagnosis, course and prognosis, and therapy--The French National Congenital Myasthenic Syndrome Network experience]

Congenital myasthenic syndromes (CMS) are a heterogeneous group of disorders caused by genetic defects affecting neuromuscular transmission and leading to muscle weakness accentuated by exertion. Three different aspects have been investigated by members of the national French CMS Network: the difficulties in making a proper diagnosis; the course and long-term prognosis; and the response to therapy, especially for CMS that do not respond to cholinesterase inhibitors. CMS diagnosis is late in most cases because of confusion with other entities such as: congenital myopathies, due to the frequent presentation in patients of myopathies such as permanent muscle weakness, atrophy and scoliosis, and the abnormalities of internal structure, diameter and distribution of fibers (type I predominance, type II atrophy) seen on biopsy; seronegative autoimmune myasthenia gravis, when CMS is of late onset; and metabolic myopathy, with the presence of lipidosis in muscle. The long-term prognosis of CMS was studied in a series of 79 patients recruited with the following gene mutations: CHRNA; CHRNE; DOK7; COLQ; RAPSN; AGRN; and MUSK. Disease-course patterns (progressive worsening, exacerbation, stability, improvement) could be variable throughout life in a given patient. DOK7 patients had the most severe disease course with progressive worsening: of the eight wheelchair-bound and ventilated patients, six had mutations of this gene. Pregnancy was a frequent cause of exacerbation. Anticholinesterase agents are the first-line therapy for CMS patients, except for cases of slow-channel CMS, COLQ and DOK7. In our experience, 3,4-DAP was a useful complement for several patients harboring CMS with AChR loss or RAPSN gene mutations. Ephedrine was given to 18 patients (eight DOK7, five COLQ, four AGRN and one RAPSN). Tolerability was good. Therapeutic responses were encouraging even in the most severely affected patients, particularly with DOK7 and COLQ. Salbutamol was a good alternative in one patient who was allergic to ephedrine.

Absence of mutation in the SLC2A1 gene in a cohort of patients with alternating hemiplegia of childhood (AHC)

Alternating hemiplegia of childhood (AHC) is a rare neuropediatric disorder classically characterized by episodes of hemiplegia developing in the first months of life, various non-epileptic paroxysmal events and global neurological impairment. If the etiology is unresolved, the disorder is highly suspected to be monogenic with DE NOVO autosomal dominant mutations. A missense mutation in the SLC2A1 gene encoding the facilitative glucose transporter-1 (GLUT1) was recently described in a child fulfilling the existing criteria for the diagnosis of AHC, with the exception of age at onset, thus suggesting a clinical overlap between AHC and GLUT1 deficiency syndrome due to SLC2A1 mutations. We have studied a cohort of 23 patients to investigate whether patients with classical AHC harbor SLC2A1 mutations. Automated Sanger sequencing and MLPA analyses failed to detect any SLC2A1 mutations in the 23 patients analyzed, thus excluding mutations of this gene as a frequent cause of classical AHC.

Schwartz-Jampel syndrome and perlecan deficiency

Schwartz-Jampel syndrome (SJS) is a rare autosomal recessive disorder characterized by the association of myotonia with chondrodysplasia. A positional cloning strategy allowed the localization and the identification of perlecan as the disease causing gene. Another human recessive disorder, the Dyssegmental Dysplasia, Silverman-Handmaker type (DDSH), is caused by functional null mutations of the perlecan gene. A gene-dosage effect seems to account for the correlation between the phenotype and the mutations within the gene: SJS would be associated with hypomorph mutations of the perlecan gene and DDSH would be due to the absence of functional perlecan. Perlecan is the major heparan sulfate proteoglycan of extracellular matrix and basement membranes that displays various functions. Based on these functions, several hypotheses are evoked to explain chondrodysplasia and the unusual myotonia in SJS. Mouse models are invaluable tools to explore these hypotheses. Since knock-out mice develop a phenotype similar to DDSH, we have developed a SJS mouse model by reproducing the hypomorph effect of SJS perlecan mutation in this species. The characterization of this mouse model will help to understand the pathophysiological mechanism leading to this multisystemic human disorder.

Hypokalaemic periodic paralysis type 2 caused by mutations at codon 672 in the muscle sodium channel gene SCN4A

Hypokalaemic periodic paralysis (hypoPP) is an autosomal dominant muscle disorder characterized by episodic attacks of muscle weakness associated with a decrease in blood potassium levels. Mutations in the gene encoding the skeletal muscle voltage-gated calcium channel alpha-1 subunit (CACNL1A3) account for the majority of cases. Recently, mutations in the gene coding for the skeletal muscle voltage-gated sodium channel alpha subunit (SCN4A) have been reported in a small number of hypoPP families. In order to determine the relative frequency of the CANCL1A3 and SCN4A mutations in a large population of hypoPP patients, and to specify the clinical and pathological features associated with each of them, we searched for mutations in 58 independent hypoPP index cases. We detected the causative mutation in 45 cases: 40 were linked to the CACNL1A3 gene and five to the SCN4A gene. One mutation has not been described before. Some remarkable clinical features were observed in a large hypoPP family carrying an SCN4A mutation: a complete penetrance in men and women, an early age at onset, postcritic myalgias and an increased number and severity of attacks induced by acetazolamide. A muscle biopsy, performed in two members of this family, revealed a peculiar myopathy characterized by tubular aggregates. In contrast, vacuoles were predominant in muscles from hypoPP patients carrying CACNL1A3 mutations. Our findings point to the usefulness of a molecular characterization of hypoPP patients in clinical practice. They also provide new clues for understanding the mechanisms behind functional and structural alterations of the skeletal muscle in hypoPP.

Expression of SMARCF1, a truncated form of SWI1, in neuroblastoma

Previously we cloned and mapped a B120 gene to human chromosome 1p35-36.1 where possible suppressor genes for various neuroendocrine tumors including neuroblastoma have been mapped. Very recently, B120 was identified as a truncated form of p270, a putative human counterpart of SWI1. In the present study, expression of the B120 gene product was immunohistochemically investigated in 23 neuroblastomas. We also examined B120 expression in neural stem cells in developing brain and intact adrenal medulla. Four of 23 neuroblastomas strongly expressed B120 gene product in both cytoplasm and nucleus. The other neuroblastomas expressed B120 gene product in the nucleus; however, the intensity of staining was much weaker and equivalent to that in developing human brain stem cells in the subventricular region. B120 gene product was less strongly expressed in intact adrenal medulla. Subsequently, we performed loss of heterozygosity studies on 19 neuroblastomas using the polymorphic markers D1S195 and D1S511 located near the B120 gene. Loss of heterozygosity was observed in three of 19 tumors that abundantly expressed B120 protein. Furthermore, neuroblastoma cells were transfected with B120 expression vector. These transfected neuroblastoma cells adhered to each other and aggregated. Differential display experiments followed by reverse transcriptase-polymerase chain reaction and Northern blot analysis were performed and three molecules with altered expression in B120-transfected neuroblastoma cells were identified. One of three genes seemed to be a proliferation-related and cell cycle-related nucleolar protein, p120, encoding gene. We further characterized the genomic structure of B120. B120 appeared to be encoded by 17 exons in more than 20-kbp genomic DNA. The present findings contribute to understanding of the B120 gene, a truncated form of human SWII1, an approved term for which is SMARCF1, in normal cells and neuroblastomas.

Perlecan, the major proteoglycan of basement membranes, is altered in patients with Schwartz-Jampel syndrome (chondrodystrophic myotonia)

Schwartz-Jampel syndrome (SJS1) is a rare autosomal recessive disorder characterized by permanent myotonia (prolonged failure of muscle relaxation) and skeletal dysplasia, resulting in reduced stature, kyphoscoliosis, bowing of the diaphyses and irregular epiphyses. Electromyographic investigations reveal repetitive muscle discharges, which may originate from both neurogenic and myogenic alterations. We previously localized the SJS1 locus to chromosome 1p34-p36.1 and found no evidence of genetic heterogeneity. Here we describe mutations, including missense and splicing mutations, of the gene encoding perlecan (HSPG2) in three SJS1 families. In so doing, we have identified the first human mutations in HSPG2, which underscore the importance of perlecan not only in maintaining cartilage integrity but also in regulating muscle excitability.

Voltage-sensor sodium channel mutations cause hypokalemic periodic paralysis type 2 by enhanced inactivation and reduced current

The pathomechanism of familial hypokalemic periodic paralysis (HypoPP) is a mystery, despite knowledge of the underlying dominant point mutations in the dihydropyridine receptor (DHPR) voltage sensor. In five HypoPP families without DHPR gene defects, we identified two mutations, Arg-672-->His and -->Gly, in the voltage sensor of domain 2 of a different protein: the skeletal muscle sodium channel alpha subunit, known to be responsible for hereditary muscle diseases associated with myotonia. Excised skeletal muscle fibers from a patient heterozygous for Arg-672-->Gly displayed depolarization and weakness in low-potassium extracellular solution. Slowing and smaller size of action potentials were suggestive of excitability of the wild-type channel population only. Heterologous expression of the two sodium channel mutations revealed a 10-mV left shift of the steady-state fast inactivation curve enhancing inactivation and a sodium current density that was reduced even at potentials at which inactivation was removed. Decreased current and small action potentials suggested a low channel protein density. The alterations are decisive for the pathogenesis of episodic muscle weakness by reducing the number of excitable sodium channels particularly at sustained membrane depolarization. The results prove that SCN4A, the gene encoding the sodium channel alpha subunit of skeletal muscle is responsible for HypoPP-2 which does not differ clinically from DHPR-HypoPP. HypoPP-2 represents a disease caused by enhanced channel inactivation and current reduction showing no myotonia.

The human CDC42 gene: genomic organization, evidence for the existence of a putative pseudogene and exclusion as a SJS1 candidate gene

Schwartz-Jampel syndrome (SJS) is an autosomal recessive human disorder characterized by myotonia and osteoarticular deformities. Three types are distinguished based on age at onset: types 1A, 1B and 2. We have previously localized the SJS1 gene, responsible for types 1A and 1B, on human chromosome 1p35-p36.1 in a region frequently rearranged in human tumours. The CDC42 gene, for which divergent localizations have previously been described (chromosomes 4, 7 and 20), has been mapped within the SJS1 critical interval by radiation hybrid and yeast/P1 artificial-chromosome-based physical map analyses. The CDC42 gene product is a small GTPase protein of the Rho family mediating a variety of signaling pathways including cytoskeletal rearrangements, cell-cycle progression and transformation. To search for mutations in SJS1 patients, we have determined the organization of the human CDC42 gene on chromosome 1p and found that it encodes for the placental and brain isoforms generated by alternative splicing. No mutations have been found in SJS1 patients, excluding CDC42 as the SJS1 gene. Interestingly, we have demonstrated that a CDC42-like transcript gene located on chromosome 4 does not contain introns and is similar to the placental isoform, suggesting that it is a processed pseudogene. The determination of the CDC42 gene structure described in this report should facilitate future studies of the potential role of CDC42 in human disorders.

Mutation in the human acetylcholinesterase-associated collagen gene, COLQ, is responsible for congenital myasthenic syndrome with end-plate acetylcholinesterase deficiency (Type Ic)

Congenital myasthenic syndrome (CMS) with end-plate acetylcholinesterase (AChE) deficiency is a rare autosomal recessive disease, recently classified as CMS type Ic (CMS-Ic). It is characterized by onset in childhood, generalized weakness increased by exertion, refractoriness to anticholinesterase drugs, and morphological abnormalities of the neuromuscular junctions (NMJs). The collagen-tailed form of AChE, which is normally concentrated at NMJs, is composed of catalytic tetramers associated with a specific collagen, COLQ. In CMS-Ic patients, these collagen-tailed forms are often absent. We studied a large family comprising 11 siblings, 6 of whom are affected by a mild form of CMS-Ic. The muscles of the patients contained collagen-tailed AChE. We first excluded the ACHE gene (7q22) as potential culprit, by linkage analysis; then we mapped COLQ to chromosome 3p24.2. By analyzing 3p24.2 markers located close to the gene, we found that the six affected patients were homozygous for an interval of 14 cM between D3S1597 and D3S2338. We determined the COLQ coding sequence and found that the patients present a homozygous missense mutation, Y431S, in the conserved C-terminal domain of COLQ. This mutation is thought to disturb the attachment of collagen-tailed AChE to the NMJ, thus constituting the first genetic defect causing CMS-Ic.

Diseases caused by voltage-gated ion channels

Ion channels regulate the transfer of ions between the outer and the inner surface of the cell membrane. The opening of ion channels may be triggered by the binding of a ligand or variations in the membrane potential. Voltage-gated ion channels are an important class of such channels, that are involved in the generation and propagation of action potentials and play a key role in cell to cell communication. As a consequence of cloning and sequencing of ion channel genes, their role in diseases affecting excitable tissues such as the nervous system, heart and skeletal muscle has been examined, and a new class of diseases has emerged. We will review disorders caused by mutations in voltage-gated ion channels affecting these excitable tissues as well as non-excitable tissues such as the kidney. The clinician should be aware of this new class of diseases because pharmacological agents modulating channel functions are available. Characterization of these gene defects should lead to better treatment of these disorders.

Abstraction skillfulness in monozygotic and dizygotic twin pairs

The computerized version of the Wisconsin Card Sorting Test (WCST) was administered to a sample of 96 subjects (Ss), constituted in equal parts by monozygotic twins (MZ), dizygotic twins (DZ), unique children and couples of "almost contemporary" brothers. The statistic tests (Analysis of principal components, ANOVA) underline, as far as the rapidity to define a category is concerned, a statistically significant difference between DZ and singletons, independently from the fact that the latter may be unique children. A significant difference emerged neither between MZ and singletons, nor between MZ and DZ.

Recessive Schwartz-Jampel syndrome (SJS): confirmation of linkage to chromosome 1p, evidence of genetic homogeneity and reduction of the SJS locus to a 3-cM interval

Schwartz-Jampel syndrome (SJS), or chondrodystrophic myotonia, is a rare autosomal recessive disorder characterized by generalized myotonia resulting in a particular, recognizable facies and osteoarticular abnormalities. Some of us have recently shown genetic linkage of SJS to a locus on 1p34-p36.1 in five families. Here, we show by homozygosity mapping and segregation analysis that eight new families are most likely linked to the SJS locus on chromosome 1, confirming the localization of SJS to chromosome 1p and suggesting genetic homogeneity. Recombination events reduced the SJS locus from a genetic interval of 8 to 3 cM, which should facilitate the identification of the SJS gene. Low clinical variability was observed between the studied families, except for osteoarticular abnormalities. Since the severity and the location of osteoarticular abnormalities varied from one individual to another, even in the same families, other factors than the SJS gene itself, genetic or epigenetic, might contribute to the phenotype.

Localization of the Schwartz-Jampel syndrome (SJS) locus to chromosome 1p34-p36.1 by homozygosity mapping

Schwartz-Jampel syndrome (SJS, MIM 255800), also known as chondrodystrophic myotonia, is a rare autosomal recessive disorder characterized by generalized myotonia, skeletal abnormalities and facial dysmorphism. Using homozygosity mapping, we localized the SJS locus to chromosome 1p34-p36.1 in a 8 cM interval flanked by markers D1S199 and D1S234. Families of different ethnic backgrounds (Tunisia and South Africa) showed genetic linkage to the same locus. Moreover, one Algerian family also demonstrated evidence of genetic linkage to 1p34-p36.1. Taken altogether, our results suggest genetic homogeneity, at least in the group of families analyzed.

Self-awareness in monozygotic twins: a relational study

This study considers the replies to a 14-item questionnaire, by 27 monozygotic (MZ) and 38 dizygotic (DZ) pairs. Another sample consisting of 48 sets of parents of twins (24 of whom were MZ and 24 DZ, not necessarily corresponding to the couples of twins actually studied) was used, to answer a questionnaire directly related the one put to the twin pairs. The results of statistical tests performed (canonical correlation and Fisher's discriminant) indicate that only in MZ twins does self-awareness outweigh pair-awareness. This does not seem to be related to any difference between MZ and DZ twins in the education/upbringing received from their parents.

[Case of mucocele causing exophthalmos. Diagnostic considerations]

A case of ethmoid mucocele with exophthalmos as isolated symptom is reported. Clinical, aetiopathological and radiological features are evaluated; particularly computed tomography findings can be an available help in diagnosis.

Orbital pseudotumor. Pathologic and therapeutic considerations

Orbital pseudotumor is a chronic, idiopathic granuloma acting as an orbital expanding lesion. The importance of clinical features for a proper diagnosis is relevant. A subdivision in three subgroups is made taking in account surgical, pathological and CT-scan patterns. Therapeutic indications are given according to the follow-up of 29 cases.

31 primary orbital mass lesions in infancy and childhood

A series of 31 primary orbital mass lesions in patients up to 15 years of age is presented (malignancies: 5 sarcomas, 1 retinoblastoma; benign lesions: 7 optic nerve gliomas, 4 pseudotumors, 4 angiomas, 3 fibrous dysplasias, 2 dermoids, 1 hemiangioblastoma, 1 osteoma, 1 neurofibroma, 1 eosinophilic granuloma, 1 echinococcus). All the patients were operated upon using the subfrontal-extradural approach. The pathological and roentgenological features, and the long-term follow-up are analyzed. In the author's experience, computerized tomography scan (CT scan) is useful in planning the surgical approach more than in the pathological differential diagnosis. In orbital pseudotumors, without visual function impairment, CT scan is also useful in checking the results of conservative steroid therapy. The author's stress the importance of performing radical surgery, either along with (in benign lesions, including optic nerve gliomas) or followed by radiotherapy (in malignancies).

[Primary intraorbital meningiomas]

The authors found in literature the description of 124 cases of intra-orbital primitive meningiomas; they illustrate their clinico-surgical aspects as well as the differential features on the ground of their point of origin: 90 meningiomas of the (dural) sheath of the optic nerve (23 intraforaminal ones and 67 extraforaminal ones), 34 extradural meningiomas; they present 4 original cases, 3 extradural ones and 1 of the sheath of the optic nerve. After describing the elements of differential diagnosis with the most common intra-orbital expansive lesions (gliomas, sarcomas, angiomas, psuedotumors or orbital granulomas) the authors end by stating that total extirpation must be always carried out including, if necessary, the optic nerve and the ocular globe when it is invaded.

Lymphocytic infiltration in long-survival glioblastomas: possible host's resistance

A series of 200 patients operated on at the Rome University Neurosurgical Clinic for primary glioblastoma is analyzed. Eight of these patients (4%) survived for over four years. The histological preparations showed more or less heavy perivascular lymphocytic infiltration in six of these cases. Since such infiltrations in malignant tumours of other organs are recognized as having an immune function, expressing the host's resistance to his tumour, the longer survival of the cases considered may well denote an immune defensive mechanism.