CIBERER: Spanish National Network for Research on Rare Diseases: a highly productive collaborative initiative

CIBER (Center for Biomedical Network Research; Centro de Investigación Biomédica En Red) is a public national consortium created in 2006 under the umbrella of the Spanish National Institute of Health Carlos III (ISCIII). This innovative research structure comprises 11 different specific areas dedicated to the main public health priorities in the National Health System. CIBERER, the thematic area of CIBER focused on rare diseases (RDs) currently consists of 75 research groups belonging to universities, research centers, and hospitals of the entire country. CIBERER's mission is to be a center prioritizing and favoring collaboration and cooperation between biomedical and clinical research groups, with special emphasis on the aspects of genetic, molecular, biochemical, and cellular research of RDs. This research is the basis for providing new tools for the diagnosis and therapy of low‐prevalence diseases, in line with the International Rare Diseases Research Consortium (IRDiRC) objectives, thus favoring translational research between the scientific environment of the laboratory and the clinical setting of health centers. In this article, we intend to review CIBERER's 15‐year journey and summarize the main results obtained in terms of internationalization, scientific production, contributions toward the discovery of new therapies and novel genes associated to diseases, cooperation with patients' associations and many other topics related to RD research.

Clinical and genetic characteristics of 21 Spanish patients with biallelic pathogenic SPG7 mutations

Spastic paraplegia type 7 (SPG7) is one of the most common hereditary spastic paraplegias. SPG7 mutations most often lead to spastic paraparesis (HSP) and/or hereditary cerebellar ataxia (HCA), frequently with mixed phenotypes. We sought to clinically and genetically characterize a Spanish cohort of SPG7 patients. Patients were recruited from our HCA and HSP cohorts. We identified twenty-one patients with biallelic pathogenic SPG7 mutations. Mean age at onset was 37.4 years (SD ± 14.3). The most frequent phenotype was spastic ataxia (57%), followed by pure spastic paraplegia (19%) and complex phenotypes (19%). Isolated patients presented with focal or multifocal dystonia, subclinical myopathy or ophthalmoplegia. p.Ala510Val was the most frequent pathogenic variant encountered. Compound heterozygous for p.Ala510Val displayed younger onset (p < 0.05) and more complex phenotypes (p < 0.05) than p.Ala510Val homozygotes. Two novel variants were found: p.Lys559Argfs*33 and p.Ala312Glu. In conclusion, spastic ataxia is the most common phenotype found in Spanish patients. Nonetheless, SPG7 analysis should also be considered in patients with less frequent clinical findings such as dystonia or ophthalmoplegia especially when these symptoms are associated with mild spastic ataxia.

Clinical and genetic spectrum of a large cohort of patients with δ-sarcoglycan muscular dystrophy

Sarcoglycanopathies include four subtypes of autosomal recessive limb-girdle muscular dystrophies (LGMDR3, LGMDR4, LGMDR5 and LGMDR6) that are caused, respectively, by mutations in the SGCA, SGCB, SGCG and SGCD genes. Delta-sarcoglycanopathy (LGMDR6) is the least frequent and is considered an ultra-rare disease. Our aim was to characterize the clinical and genetic spectrum of a large international cohort of LGMDR6 patients and to investigate whether or not genetic or protein expression data could predict diseasés severity. This is a retrospective study collecting demographic, genetic, clinical and histological data of patients with genetically confirmed LGMDR6 including protein expression data from muscle biopsies. We contacted 128 pediatric and adult neuromuscular units around the world that reviewed genetic data of patients with a clinical diagnosis of a neuromuscular disorder. We identified 30 patients with a confirmed diagnosis of LGMDR6 of which 23 patients were included in this study. Eighty seven percent of the patients had consanguineous parents. Ninety one percent of the patients were symptomatic at the time of the analysis. Proximal muscle weakness of the upper and lower limbs was the most common presenting symptom. Distal muscle weakness was observed early over the course of the disease in 56.5% of the patients. Cardiac involvement was reported in 5 patients (21.7%) and 4 patients (17.4%) required non-invasive ventilation. Sixty percent of patients were wheelchair-bound since early teens (median age of 12.0 years old). Patients with absent expression of the sarcoglycan complex on muscle biopsy had a significant earlier onset of symptoms and an earlier age of loss of ambulation compared to patients with residual protein expression. This study confirmed that delta-sarcoglycanopathy is an ultra-rare neuromuscular condition and described the clinical and molecular characteristics of the largest yet-reported collected cohort of patients. Our results showed that this is a very severe and quickly progressive disease characterized by generalized muscle weakness affecting predominantly proximal and distal muscles of the limbs. Similar to other forms of sarcoglycanopathies, the severity and rate of progressive weakness correlates inversely with the abundance of protein on muscle biopsy.

Meta-analyses of ataluren randomized controlled trials in nonsense mutation Duchenne muscular dystrophy

Aim: Assess the totality of efficacy evidence for ataluren in patients with nonsense mutation Duchenne muscular dystrophy (nmDMD). Materials & methods: Data from the two completed randomized controlled trials (ClinicalTrials.gov: NCT00592553; NCT01826487) of ataluren in nmDMD were combined to examine the intent-to-treat (ITT) populations and two patient subgroups (baseline 6-min walk distance [6MWD] ≥300–<400 or <400 m). Meta-analyses examined 6MWD change from baseline to week 48. Results: Statistically significant differences in 6MWD change with ataluren versus placebo were observed across all three meta-analyses. Least-squares mean difference (95% CI): ITT (n = 342), +17.2 (0.2–34.1) m, p = 0.0473; ≥300–<400 m (n = 143), +43.9 (18.2–69.6) m, p = 0.0008; <400 m (n = 216), +27.7 (6.4–49.0) m, p = 0.0109. Conclusion: These meta-analyses support previous evidence for ataluren in slowing disease progression versus placebo in patients with nmDMD over 48 weeks. Treatment benefit was most evident in patients with a baseline 6MWD ≥300–<400 m (the ambulatory transition phase), thereby informing future trial design.

Clinical, pathological and genetic spectrum in 89 cases of mitochondrial progressive external ophthalmoplegia

BACKGROUND

Mitochondrial progressive external ophthalmoplegia (PEO) encompasses a broad spectrum of clinical and genetic disorders. We describe the phenotypic subtypes of PEO and its correlation with molecular defects and propose a diagnostic algorithm.

METHODS

Retrospective analysis of the clinical, pathological and genetic features of 89 cases.

RESULTS

Three main phenotypes were found: 'pure PEO' (42%), consisting of isolated palpebral ptosis with ophthalmoparesis; Kearns-Sayre syndrome (10%); and 'PEO plus', which associates extraocular symptoms, distinguishing the following subtypes: : myopathic (33%), bulbar (12%) and others (3%). Muscle biopsy was the most accurate test, showing mitochondrial changes in 95%. Genetic diagnosis was achieved in 96% of the patients. Single large-scale mitochondrial DNA (mtDNA) deletion was the most frequent finding (63%), followed by multiple mtDNA deletions (26%) due to mutations in TWNK (n=8), POLG (n=7), TK2 (n=6) or RRM2B (n=2) genes, and point mtDNA mutations (7%). Three new likely pathogenic mutations were identified in the TWNK and MT-TN genes.

CONCLUSIONS

Phenotype-genotype correlations cannot be brought in mitochondrial PEO. Muscle biopsy should be the first step in the diagnostic flow of PEO when mitochondrial aetiology is suspected since it also enables the study of mtDNA rearrangements. If no mtDNA deletions are identified, whole mtDNA sequencing should be performed.

A Roma founder BIN1 mutation causes a novel phenotype of centronuclear myopathy with rigid spine

OBJECTIVE

To describe a large series of BIN1 patients, in which a novel founder mutation in the Roma population of southern Spain has been identified.

METHODS

Patients diagnosed with centronuclear myopathy (CNM) at 5 major reference centers for neuromuscular disease in Spain (n = 53) were screened for BIN1 mutations. Clinical, histologic, radiologic, and genetic features were analyzed.

RESULTS

Eighteen patients from 13 families carried the p.Arg234Cys variant; 16 of them were homozygous for it and 2 had compound heterozygous p.Arg234Cys/p.Arg145Cys mutations. Both BIN1 variants have only been identified in Roma, causing 100% of CNM in this ethnic group in our cohort. The haplotype analysis confirmed all families are related. In addition to clinical features typical of CNM, such as proximal limb weakness and ophthalmoplegia, most patients in our cohort presented with prominent axial weakness, often associated with rigid spine. Severe fat replacement of paravertebral muscles was demonstrated by muscle imaging. This phenotype seems to be specific to the p.Arg234Cys mutation, not reported in other BIN1 mutations. Extreme clinical variability was observed in the 2 compound heterozygous patients for the p.Arg234Cys/p.Arg145Cys mutations, from a congenital onset with catastrophic outcome to a late-onset disease. Screening of European Roma controls (n = 758) for the p.Arg234Cys variant identified a carrier frequency of 3.5% among the Spanish Roma.

CONCLUSION

We have identified a BIN1 founder Roma mutation associated with a highly specific phenotype, which is, from the present cohort, the main cause of CNM in Spain.

ANKK1 is found in myogenic precursors and muscle fibers subtypes with glycolytic metabolism

Ankyrin repeat and kinase domain containing 1 (ANKK1) gene has been widely related to neuropsychiatry disorders. The localization of ANKK1 in neural progenitors and its correlation with the cell cycle has suggested its participation in development. However, ANKK1 functions still need to be identified. Here, we have further characterized the ANKK1 localization in vivo and in vitro, by using immunolabeling, quantitative real-time PCR and Western blot in the myogenic lineage. Histologic investigations in mice and humans revealed that ANKK1 is expressed in precursors of embryonic and adult muscles. In mice embryos, ANKK1 was found in migrating myotubes where it shows a polarized cytoplasmic distribution, while proliferative myoblasts and satellite cells show different isoforms in their nuclei and cytoplasm. In vitro studies of ANKK1 protein isoforms along the myogenic progression showed the decline of nuclear ANKK1-kinase until its total exclusion in myotubes. In adult mice, ANKK1 was expressed exclusively in the Fast-Twitch muscles fibers subtype. The induction of glycolytic metabolism in C2C12 cells with high glucose concentration or treatment with berberine caused a significant increase in the ANKK1 mRNA. Similarly, C2C12 cells under hypoxic conditions caused the increase of nuclear ANKK1. These results altogether show a relationship between ANKK1 gene regulation and the metabolism of muscles during development and in adulthood. Finally, we found ANKK1 expression in regenerative fibers of muscles from dystrophic patients. Future studies in ANKK1 biology and the pathological response of muscles will reveal whether this protein is a novel muscle disease biomarker.

Audiological Findings in Charcot-Marie-Tooth Disease Type 4C

OBJECTIVE

Charcot-Marie-Tooth disease type 4C (CMT4C) is a hereditary demyelinating early onset neuropathy with prominent unsteadiness and occasional cranial nerve involvement. Vestibulopathy caused by the dysfunction of cranial nerve VIII has been demonstrated in a high percentage of these patients, but the presence and degree of auditory neuropathy are unknown. The aim of the study was to characterize the hearing abnormalities of a series of patients with CMT4C and to determine the presence and severity of auditory neuropathy (AN) in these patients.

MATERIALS AND METHODS

Ten patients with genetically confirmed CMT4C underwent comprehensive clinical and audiological testing. The results were compared among patients in different age groups and also to the results of vestibular testing that had already been performed.

RESULTS

Only 3 patients had hearing problems, but 9 had hearing abnormalities on ancillary testing that were compatible with different degrees of auditory nerve dysfunction. In the mildest cases, only the abnormality of the stapedial reflex and distortion of wave I in auditory brainstem responses could be detected. In the more severe cases, tonal audiometry revealed asymmetric hearing loss. These findings were more severe in older patients, even after correcting for age-related hypoacusia. In these patients, vestibular dysfunction could also be detected and seemed to be more profound and symmetric than hearing loss.

CONCLUSION

This report confirms and defines the presence of different degrees of auditory neuropathy in all patients with CMT4C, being detectable, usually unilaterally, during infancy, and worsening with disease progression.

Netrin-1 receptor antibodies in thymoma-associated neuromyotonia with myasthenia gravis

OBJECTIVE

To identify cell-surface antibodies in patients with neuromyotonia and to describe the main clinical implications.

METHODS

Sera of 3 patients with thymoma-associated neuromyotonia and myasthenia gravis were used to immunoprecipitate and characterize neuronal cell-surface antigens using reported techniques. The clinical significance of antibodies against precipitated proteins was assessed with sera of 98 patients (neuromyotonia 46, myasthenia gravis 52, thymoma 42; 33 of them with overlapping syndromes) and 219 controls (other neurologic diseases, cancer, and healthy volunteers).

RESULTS

Immunoprecipitation studies identified 3 targets, including the Netrin-1 receptors DCC (deleted in colorectal carcinoma) and UNC5A (uncoordinated-5A) as well as Caspr2 (contactin-associated protein-like 2). Cell-based assays with these antigens showed that among the indicated patients, 9 had antibodies against Netrin-1 receptors (7 with additional Caspr2 antibodies) and 5 had isolated Caspr2 antibodies. Only one of the 219 controls had isolated Caspr2 antibodies with relapsing myelitis episodes. Among patients with neuromyotonia and/or myasthenia gravis, the presence of Netrin-1 receptor or Caspr2 antibodies predicted thymoma (p < 0.05). Coexisting Caspr2 and Netrin-1 receptor antibodies were associated with concurrent thymoma, myasthenia gravis, and neuromyotonia, often with Morvan syndrome (p = 0.009). Expression of DCC, UNC5A, and Caspr2 proteins was demonstrated in paraffin-embedded thymoma samples (3) and normal thymus.

CONCLUSIONS

Antibodies against Netrin-1 receptors (DCC and UNC5a) and Caspr2 often coexist and associate with thymoma in patients with neuromyotonia and myasthenia gravis.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that antibodies against Netrin-1 receptors can identify patients with thymoma (sensitivity 21.4%, specificity 100%).

Mutations in the MORC2 gene cause axonal Charcot-Marie-Tooth disease

Charcot-Marie-Tooth disease (CMT) is a complex disorder with wide genetic heterogeneity. Here we present a new axonal Charcot-Marie-Tooth disease form, associated with the gene microrchidia family CW-type zinc finger 2 (MORC2). Whole-exome sequencing in a family with autosomal dominant segregation identified the novel MORC2 p.R190W change in four patients. Further mutational screening in our axonal Charcot-Marie-Tooth disease clinical series detected two additional sporadic cases, one patient who also carried the same MORC2 p.R190W mutation and another patient that harboured a MORC2 p.S25L mutation. Genetic and in silico studies strongly supported the pathogenicity of these sequence variants. The phenotype was variable and included patients with congenital or infantile onset, as well as others whose symptoms started in the second decade. The patients with early onset developed a spinal muscular atrophy-like picture, whereas in the later onset cases, the initial symptoms were cramps, distal weakness and sensory impairment. Weakness and atrophy progressed in a random and asymmetric fashion and involved limb girdle muscles, leading to a severe incapacity in adulthood. Sensory loss was always prominent and proportional to disease severity. Electrophysiological studies were consistent with an asymmetric axonal motor and sensory neuropathy, while fasciculations and myokymia were recorded rather frequently by needle electromyography. Sural nerve biopsy revealed pronounced multifocal depletion of myelinated fibres with some regenerative clusters and occasional small onion bulbs. Morc2 is expressed in both axons and Schwann cells of mouse peripheral nerve. Different roles in biological processes have been described for MORC2. As the silencing of Charcot-Marie-Tooth disease genes have been associated with DNA damage response, it is tempting to speculate that a deregulation of this pathway may be linked to the axonal degeneration observed in MORC2 neuropathy, thus adding a new pathogenic mechanism to the long list of causes of Charcot-Marie-Tooth disease.

Limb-girdle muscular dystrophy 1F is caused by a microdeletion in the transportin 3 gene

In 2001, we reported linkage of an autosomal dominant form of limb-girdle muscular dystrophy, limb-girdle muscular dystrophy 1F, to chromosome 7q32.1-32.2, but the identity of the mutant gene was elusive. Here, using a whole genome sequencing strategy, we identified the causative mutation of limb-girdle muscular dystrophy 1F, a heterozygous single nucleotide deletion (c.2771del) in the termination codon of transportin 3 (TNPO3). This gene is situated within the chromosomal region linked to the disease and encodes a nuclear membrane protein belonging to the importin beta family. TNPO3 transports serine/arginine-rich proteins into the nucleus, and has been identified as a key factor in the HIV-import process into the nucleus. The mutation is predicted to generate a 15-amino acid extension of the C-terminus of the protein, segregates with the clinical phenotype, and is absent in genomic sequence databases and a set of >200 control alleles. In skeletal muscle of affected individuals, expression of the mutant messenger RNA and histological abnormalities of nuclei and TNPO3 indicate altered TNPO3 function. Our results demonstrate that the TNPO3 mutation is the cause of limb-girdle muscular dystrophy 1F, expand our knowledge of the molecular basis of muscular dystrophies and bolster the importance of defects of nuclear envelope proteins as causes of inherited myopathies.

Autoimmunity as a prognostic factor in sporadic adult onset cerebellar ataxia

Cerebellar adult onset ataxia is a heterogeneous condition. The aim of this study was to ascertain if there is a heightened autoimmune background in patients with sporadic cerebellar ataxia of unknown origin, and if autoimmunity correlates with a more rapid evolution of the ataxia. We selected patients with sporadic progressive adult onset cerebellar ataxia with a follow-up of >5 years. As controls we included 43 patients with genetically demonstrated hereditary ataxia. All patients were tested for a panel of neuronal (onconeuronal, glutamate-decarboxylase [GAD], IgG/IgA transglutaminase 6 antibodies) and systemic non-neuronal antibodies (including IgG/IgA gliadin and transglutaminase 2, thyroperoxidase, thyroglobulin, antinuclear, striational, smooth muscle, mitochondrial, liver kidney microsomal, and parietal gastric cells antibodies). Correlation between the antibodies and disease progression was studied with Cox regression models and Kaplan-Meier plots. Forty-four patients were included. All patients were negative for onconeuronal or GAD antibodies. There were no significant differences between patients and controls in the prevalence of transglutaminase 6, 2, gliadin, or thyroid antibodies. However, when we studied the panel of systemic non-neuronal autoantibodies as a group, antibodies were more frequent in patients with sporadic ataxia (p = 0.018). The presence of one or more systemic non-neuronal antibodies correlated with a faster evolution to stage 2 (loss of independent gait) (p = 0.03) and shorter survival (p = 0.03) in patients with sporadic ataxia. We conclude that there is probably a heightened autoimmune background in some patients with sporadic cerebellar ataxia of unknown origin. The presence of systemic non-neuronal autoantibodies is a prognostic marker.

[Guidelines for molecular diagnosis of Charcot-Marie-Tooth disease]

INTRODUCTION

Charcot-Marie-Tooth disease (CMT) is the most frequent form of inherited neuropathy. In accordance with the inheritance pattern and degree of slowing of motor conduction velocity (MCV) of the median nerve, CMT encompasses five main forms: CMT1 (autosomal dominant [AD] or X-linked transmission and MCV < 38 m/s); CMT2 (AD or X-linked transmission and MCV > 38 m/s); CMT4 (autosomal recessive [AR] and severe slowing of MCV); AR-CMT2 (AR transmission and MCV > 38 m/s); and DI-CMT (intermediate form with AD transmission and MCV between 30 and 40 m/s). In spite of its stereotyped semiological repertoire (basically, symptoms and signs of sensory-motor polyneuropathy and pes cavus), CMT seems to be one of the most complex hereditary neurodegenerative syndromes, 31 causative genes having been cloned.

DEVELOPMENT

This paper is aimed at performing a nosological review of the disease, emphasising the guidelines for its molecular diagnosis. Genetic epidemiological studies and genotypes reported in Spanish patients are revised.

CONCLUSIONS

In the great majority of CMT cases, mutations involve a reduced number of genes, namely: for CMT1, PMP22, GJB1 and MPZ; for CMT2, MFN2 and GJB1; for CMT4, GDAP1, and NDRG1, HK1 and SH3TC2 (gypsies); for AR-CMT2, GDAP1; and for DI-CMT, GJB1 and MPZ. Given their low prevalence, mutations in other pathogenic genes should be investigated after discarding the previous ones. There is no place for the indiscriminate use of diagnostic CMT genetic panels.

Phenotypical features of the p.R120W mutation in the GDAP1 gene causing autosomal dominant Charcot-Marie-Tooth disease

Mutations in the ganglioside-induced-differentiation-associated protein 1 gene (GDAP1) can cause Charcot-Marie-Tooth (CMT) disease with demyelinating (CMT4A) or axonal forms (CMT2K and ARCMT2K). Most of these mutations present a recessive inheritance, but few autosomal dominant GDAP1 mutations have also been reported. We performed a GDAP1 gene screening in a clinically well-characterized series of 81 index cases with axonal CMT neuropathy, identifying 17 patients belonging to 4 unrelated families in whom the heterozygous p.R120W was found to be the only disease-causing mutation. The main objective was to fully characterize the neuropathy caused by this mutation. The clinical picture included a mild-moderate phenotype with onset around adolescence, but great variability. Consistently, ankle dorsiflexion and plantar flexion were impaired to a similar degree. Nerve conduction studies revealed an axonal neuropathy. Muscle magnetic resonance imaging studies demonstrated selective involvement of intrinsic foot muscles in all patients and a uniform pattern of fatty infiltration in the calf, with distal and superficial posterior predominance. Pathological abnormalities included depletion of myelinated fibers, regenerative clusters and features of axonal degeneration with mitochondrial aggregates. Our findings highlight the relevance of dominantly transmitted p.R120W GDAP1 gene mutations which can cause an axonal CMT with a wide clinical profile.

MYH7 gene tail mutation causing myopathic profiles beyond Laing distal myopathy

OBJECTIVE

To describe a wide range of clinical and pathologic myopathic profiles associated with the p.K1729del mutation in the MYH7 gene, known to cause Laing distal myopathy.

METHODS

A study conducted in the Safor region (Spain), setting of a large cluster of patients. Clinical, neurophysiologic, muscle imaging, and muscle biopsy studies and MYH7 gene sequencing were investigated in 32 patients from 4 kindreds. Data from 36 deceased or nonexamined patients were collected from hospital records or relatives.

RESULTS

Onset ranged from congenital to the 6th decade. All patients presented weakness of great toe/ankle dorsiflexors and many had associated neck flexor, finger extensor, and mild facial weakness. In most cases, involvement of proximal and axial muscles was observed either clinically or by muscle imaging, sometimes giving rise to scapuloperoneal and limb-girdle syndromes. Disabling myalgias, skeletal deformities, and dilated cardiomyopathy in one patient were associated features. Life expectancy was not reduced but the spectrum of disability ranged from asymptomatic to wheelchair confined. Electromyographic neurogenic features were frequently recorded. Muscle fiber type disproportion, core/minicore lesions, and mitochondrial abnormalities were the most relevant pathologic alterations. All patients carried the p.K1729del mutation in MYH7.

CONCLUSIONS

The p.K1729del mutation in the MYH7 gene expresses notable clinical variability and electromyographic and pathologic features that can lead to the misdiagnosis of neurogenic atrophies, congenital myopathies, or mitochondrial myopathies. Mutations in genes encoding other sarcomeric and reticulo-sarcoplasmic proteins involved in calcium regulation share pathologic characteristics with our patients, suggesting a possible pathogenetic connection.

Missense mutations in the SH3TC2 protein causing Charcot-Marie-Tooth disease type 4C affect its localization in the plasma membrane and endocytic pathway

Mutations in SH3TC2 (KIAA1985) cause Charcot-Marie-Tooth disease (CMT) type 4C, a demyelinating inherited neuropathy characterized by early-onset and scoliosis. Here we demonstrate that the SH3TC2 protein is present in several components of the endocytic pathway including early endosomes, late endosomes and clathrin-coated vesicles close to the trans-Golgi network and in the plasma membrane. Myristoylation of SH3TC2 in glycine 2 is necessary but not sufficient for the proper location of the protein in the cell membranes. In addition to myristoylation, correct anchoring also needs the presence of SH3 and TPR domains. Mutations that cause a stop codon and produce premature truncations that remove most of the TPR domains are expressed as the wild-type protein. In contrast, missense mutations in or around the region of the first-TPR domain are absent from early endosomes, reduced in plasma membrane and late endosomes and are variably present in clathrin-coated vesicles. Our findings suggest that the endocytic and membrane trafficking pathway is involved in the pathogenesis of CMT4C disease. We postulate that missense mutations of SH3TC2 could impair communication between the Schwann cell and the axon causing an abnormal myelin formation.

The p.R1109X mutation in SH3TC2 gene is predominant in Spanish Gypsies with Charcot-Marie-Tooth disease type 4

Charcot-Marie-Tooth (CMT) disease type 4 (CMT4) is the name given to autosomal recessive forms of hereditary motor and sensory neuropathy (HMSN). When we began this study, three genes or loci associated with inherited peripheral neuropathies had already been identified in the European Gypsy population: HMSN-Lom (MIM 601455), HMSN-Russe (MIM 605285) and the congenital cataracts facial dysmorphism neuropathy syndrome (MIM 604168). We have carried out genetic analyses in a series of 20 Spanish Gypsy families diagnosed with a demyelinating CMT disease compatible with an autosomal recessive trait. We found the p.R148X mutation in the N-myc downstream-regulated gene 1 gene to be responsible for the HMSN-Lom in four families and also possible linkage to the HMSN-Russe locus in three others. We have also studied the CMT4C locus because of the clinical similarities and showed that in 10 families, the disease is caused by mutations located on the SH3 domain and tetratricopeptide repeats 2 (SH3TC2) gene: p.R1109X in 20 out of 21 chromosomes and p.C737_P738delinsX in only one chromosome. Moreover, the SH3TC2 p.R1109X mutation is associated with a conserved haplotype and, therefore, may be a private founder mutation for the Gypsy population. Estimation of the allelic age revealed that the SH3TC2 p.R1109X mutation may have arisen about 225 years ago, probably as the consequence of a bottleneck.

Dysferlin expression in monocytes: A source of mRNA for mutation analysis

Dysferlin protein is expressed in peripheral blood monocytes. The genomic analysis of the DYSF gene has proved to be time consuming because it has 55 exons. We designed a mutational screening strategy based on cDNA from monocytes to find out whether the mutational analysis could be performed in mRNA from a source less invasive than the muscle biopsy. We studied 34 patients from 23 families diagnosed with dysferlinopathy. The diagnosis was based on clinical findings and on the absence of protein expression using either immunohistochemistry or Western blot of skeletal muscle and/or monocytes. We identified 28 different mutations, 13 of which were novel. The DYSF mutations in both alleles were found in 30 patients and only in one allele in four. The results were confirmed using genomic DNA in 26/34 patients. This is the first report to furnish evidence of reliable mutational analysis using monocytes cDNA and constitutes a good alternative to genomic DNA analysis.

[Different phenotypes of Charcot-Marie-Tooth disease caused by mutations in the same gene. Are classical criteria for classification still valid?]

Molecular genetic research is leading to the continuous discovery of new genes and protein involved in peripheral nerves function. Simultaneously, extended clinical, neurophysiological and pathological research has yielded new genotype-phenotype correlation on Charcot-Marie-Tooth disease (CMT). This has made it possible to know that several genes can cause both demyelinating (CMT1) and axonal (CMT2) phenotypes. Those observations have questioned the validity of some current criteria for CMT classification and raise the need for new strategies for diagnosis. The discovery of Schwann cell-axon interaction is a challenge for coming years. In this review, we extensively analyzed mutations of genes that give rise to CMT1 or CMT2 phenotypes. There are at least three forms of genetic variability. MPZ gene mutations yield a real allelism, that is, CMT1 or CMT phenotypes associated to specific mutation by site or quality. GADP1 and probably NF-L gene manifest different phenotypes but only in terms of nerve conduction velocity (CV). Evidence is provided that indicates that CV reduction in GADP-1 neuropathy may be the result of axonal loss. Finally a third form of variability is present in CMTX due to the degree of clinical expression in females related with the inactivation of chromosome X.

Clinical, electrophysiological and morphological findings of Charcot-Marie-Tooth neuropathy with vocal cord palsy and mutations in the GDAP1 gene

Three Spanish families with an autosomal recessive severe hereditary motor and sensory neuropathy, showing mutations in the ganglioside-induced-differentiation-associated protein 1 (GDAP1) gene in the Charcot-Marie-Tooth (CMT) type 4A locus were studied. The disorder started in the neonatal period or early infancy with weakness and wasting of the feet and, subsequently, involvement of the hands, causing severe disability. By the late teens, some patients developed a hoarse voice and vocal cord paresis. Peripheral motor nerve conduction velocity (MNCV) could not be measured in many cases because of the absence of muscle response due to distal atrophy. However, latencies to proximal muscles were in the normal range; median MNCV was >40 m/s in those cases in which it could be measured. Sural nerve biopsy from two patients showed a pronounced depletion of myelinated fibres, regenerative clusters and signs of axonal atrophy. Additionally, a small proportion of thin myelinated fibres and proliferation of Schwann cells forming onion bulb structures were also found. Unmyelinated fibre population was markedly increased. These findings are indicative of a predominant axonal degeneration with some demyelinating features. These Spanish families share in the severe CMT clinical phenotype with some Tunisian families who also presented mutations in the GDAP1 gene and to which the CMT4A locus was originally assigned. However, our families differ in the presence of laryngeal involvement and values of MNCV and pathological features are more in line with CMT2 type. The possibility that GDAP1 gene mutations could be expressed under different phenotypes is a question to be resolved.

The gene encoding ganglioside-induced differentiation-associated protein 1 is mutated in axonal Charcot-Marie-Tooth type 4A disease

We identified three distinct mutations and six mutant alleles in GDAP1 in three families with axonal Charcot-Marie-Tooth (CMT) neuropathy and vocal cord paresis, which were previously linked to the CMT4A locus on chromosome 8q21.1. These results establish the molecular etiology of CMT4A (MIM 214400) and suggest that it may be associated with both axonal and demyelinating phenotypes.

Genotype and phenotype analysis of Friedreich's ataxia compound heterozygous patients

Friedreich's ataxia is caused by mutations in the FRDA gene that encodes frataxin, a nuclear-encoded mitochondrial protein. Most patients are homozygous for the expansion of a GAA triplet repeat within the FRDA gene, but a few patients show compound heterozygosity for a point mutation and the GAA-repeat expansion. We analyzed DNA samples from a cohort of 241 patients with autosomal recessive or isolated spinocerebellar ataxia for the GAA triplet expansion. Patients heterozygous for the GAA expansion were screened for point mutations within the FRDA coding region. Molecular analyses included the single-strand conformation polymorphism analysis, direct sequencing, and linkage analysis with FRDA locus flanking markers. Seven compound heterozygous patients were identified. In four patients, a point mutation that predicts a truncated frataxin was detected. Three of them associated classic early-onset Friedreich's ataxia with an expanded GAA allele greater than 800 repeats. The other patient associated late-onset disease at the age of 29 years with a 350-GAA repeat expansion. In two patients manifesting the classical phenotype, no changes were observed by single-strand conformation polymorphism (SSCP) analysis. Linkage analysis in a family with two children affected by an ataxic syndrome, one of them showing heterozygosity for the GAA expansion, confirmed no linkage to the FRDA locus. Most point mutations in compound heterozygous Friedreich's ataxia patients are null mutations. In the present patients, clinical phenotype seems to be related to the GAA repeat number in the expanded allele. Complete molecular definition in these patients is required for clinical diagnosis and genetic counseling.

Early onset cerebellar ataxia and preservation of tendon reflexes: clinical phenotypes associated with GAA trinucleotide repeat expanded and non-expanded genotypes

The aim of this study was to determine phenotypie characteristics of patients with early onset cerebellar ataxia (EOCA) with preserved tendon reflexes. The series comprises 25 patients, representing 10% of all ataxic patients who have been genetically studied in our laboratory since 1990. There were 11 males and 14 females. Fourteen patients were homozygous for the GAA expansion on chromosome 9q13 (group 1) and therefore a diagnosis of Friedreich's ataxia with retained reflexes (FARR) was given. The remaining 11 patients had two normal non-expanded alleles (group 2) and a working diagnosis of EOCA with retained reflexes (EOCARR) was established. Mean ages of onset were 13.7 +/- 5.9 years (3-25) for group 1 and 10.3 +/- 7.3 for group 2; the difference was not significant. Frequencies of symptoms and signs were also comparable for both groups the only significant differences being the higher frequency of nystagmus, cardiomyopathy and sensory neuropathy in group 1 patients. There was a tendency for FARR patients to have higher frequencies of hypopallesthesia in the lower limbs and skeletal deformities. In none of the cases diabetes mellitus was observed. We conclude that differentiation of FARR and EOCARR may be suspected by classical clinical and electrophysiological data and confirmed by analysis of the GAA repeat.

[Predictive value of the study of cerebro-spinal fluid in neurological diseases. Discriminant analysis of 733 cases]

INTRODUCTION

The study of cerebrospinal fluid (CSF) gives very valuable data for the diagnosis of certain neurological disorders. Objective. To discover the discriminative value of different tests and their usefulness in the study of neurological disorders.

MATERIAL AND METHODS

Discriminative multivariate analysis was used for the group of parameters obtained from study of CSF and serum in a sample of 733 patients. BO was included, CSF cytobiochemical data and five of the equations used for calculation of the synthesis of intrathecal IgG.

RESULTS

The best discriminative function was expressed as the intrathecal IgG with normal BHE. The formula of Tourtellotte was noteworthy for overestimation of the synthesis of intrathecal IgG when the albumin index indicated BHE rupture. Prospective reclassification of the 733 cases showed that these tests are well worthwhile to rule out immunologically mediated disorders (93% of the cases were correctly reclassified); they suggest the diagnosis in multiple sclerosis (66% correctly reclassified) and give very poor reliability when trying to distinguish between inflammatory infectious processes.

CONCLUSIONS

In spite of their undoubted use in supporting the clinical diagnosis, the tests used for study of the synthesis of IgG, even complemented by cytobiochemical examination of the CSF, are not in themselves sufficient for use as a discriminative test in the differential diagnosis of neurological processes.

Phenotype correlation and intergenerational dynamics of the Friedreich ataxia GAA trinucleotide repeat

The Friedreich ataxia (FA) mutation has recently been identified as an unstable trinucleotide GAA repeat present 7-22 times in the normal population but amplified as many as > 1,000 times in FA. Since it is an autosomal recessive disease, FA does not show typical features observed in other dynamic mutation disorders, such as genetic anticipation. We have analyzed the GAA repeat in 104 FA patients and 163 carrier relatives previously defined by linkage analysis. The GAA expansion was detected in all patients, most (94%) of them being homozygous for the mutation. We have demonstrated that clinical variability in FA is related to the size of the expanded alleles: milder forms of the disease-late-onset FA and FA with retained reflexes-are associated with shorter expansions, especially with the smaller of the two expanded alleles. Absence of cardiomyopathy is also associated with shorter alleles. Dynamics of the GAA repeat has been investigated in 212 parent-offspring pairs. Meiotic instability showed a sex bias: paternally transmitted alleles tend to decrease in a linear way that depends on the paternal expansion size, whereas maternal alleles can either increase or decrease. A different pattern of intergenerational variation was also observed, depending on the genetic status of the sib: patients had shorter expansions than were seen in heterozygous carriers. This finding has been interpreted as a postzygotic event. Finally, we have observed that the size of the expansion remains constant in the population through carriers.

Mutational analysis of the MPZ, PMP22 and Cx32 genes in patients of Spanish ancestry with Charcot-Marie-Tooth disease and hereditary neuropathy with liability to pressure palsies

Charcot-Marie-Tooth disease (CMT) and hereditary neuropathy with liability to pressure palsies (HNPP) are two inherited peripheral neuropathies. The most prevalent mutations are a reciprocal 1.5-Mb duplication and 1.5-Mb deletion, respectively, at the CMT1A/HNPP locus on chromosome 17p11.2. Point mutations in the coding region of the myelin genes, peripheral myelin protein 22 (PMP22), myelin protein zero (MPZ) or connexin 32 (Cx32) have been reported in CMT patients, including CMT type 1 (CMT1), CMT type 2 (CMT2) and Déjérine-Sottas neuropathy (DS) patients, and only in the coding region of PMP22 in HNPP families lacking a deletion. We have investigated point and small mutations in the MPZ, PMP22 and Cx32 genes in a series of patients of Spanish ancestry: 47 CMT patients without duplications, and 5 HNPP patients without deletions. We found 15 different mutations in 16 CMT patients (34%). Nine different mutations in ten patients were detected in the Cx32 gene, this being the most frequently involved gene in this series, whereas five mutations involved the MPZ gene and only one the PMP22 gene. Six out of nine nucleotide substitutions in the Cx32 gene involved two codons encoding arginine at positions 164 and 183, suggesting that these two codons may constitute two Cx32 regions prone to mutate in the Spanish population. Analysis of HNPP patients revealed a 5' splicing mutation in intron 1 of the PMP22 gene in a family with autosomal dominance, which confirms allelic heterogeneity in HNPP. Ectopic mRNA analysis on leukocytes suggests that this mutation might behave as a null allele.

[Analysis of the situation of Valencian neurology by the Commission of Analysis of the Quality of Valencian Neurological Society]

INTRODUCTION

The Comision de Analisis de la Calidad de la Sociedad Valenciana de Neurologia has made a proposal of Neurology care requirements, based on the findings of various studies done in this region. There studies suggest that there should be a proportion of 3 neurologists per 100,000 inhabitants.

METHOD

An analysis of requirements was made, based on evaluation of the public health service, private practice and trainee specialists (MIR) regarding this problem. The need for emergency neurological attention, and the place of a hierarchy and a system for referral was also considered.

RESULTS

It was calculated that 109 neurologists are required, 11 in Castellon, 63 in Valencia and 35 in Alicante. This would mean a proportion of 2,66 neurologists per 100,000 inhabitants in Castellon, 2,90 in Valencia and 2,70 in Alicante. The total figure for the whole Community would be 2,82 per 100,000 inhabitants.

CONCLUSIONS

At the present time neurological care is expensive, since a lack of specialists means waiting lists, poor patient care and high costs due to inappropriate use of technical resources.

[Magnetic resonance of the brain in encephalitis due to Epstein-Barr virus]

Encephalitis due to Epstein-Barr virus (EEBV) is rare and the debate on possible pathogenic mechanisms has remained open in the absence of structural changes in brain images and discrepancies in serology and viral culture results. We describe an EEBV case in which magnetic resonance images in T1 and T2 potentiated sequences were normal, although intense meningeal captation and a destructive parenchymatous lesion could be observed after administration of gadolinium. These findings suggest direct infiltration of the central nervous system by the virus as well as a meningeal infiltrative type reaction, supporting the hypothesis that the pathogenic mechanisms involved is invasive rather than infectiously or immunologically mediated. The pattern of involvement seen in EEBV by magnetic resonance is different from that of other forms of viral encephalitis.

[Deletion of 17p11.2 chromosome in Spanish families with hereditary neuropathy and abnormal sensitivity to pressure]

Hereditary neuropathy with abnormal liability to pressure palsies (HNPP) is a dominant autosomally transmitted disease that gives rise to foci of peripheral nerve myelination, reducing conduction and leading to episodes of palsy and sensory changes that are all linked to sensitivity to pressure and traction on the affected nerve roots. The molecular basis of HNPP has been identified as a submicroscopic deletion of the 17p11.2 chromosome in exactly the same region that it is duplicated in Charcot-Marie-Tooth disease, type 1A (CMT1A). We report genetic analyses of 13 patients (belonging to 3 families) diagnosed of HNPP by means of physical examination and electrophysiologic and morphologic tests (the last in 3 cases only). Inter- and intrafamilial variation in symptomatology was studied. Some patients presented the usual clinical signs, such as recidivating brachial plexus palsy, permanent sensory polyneuropathy, foot deformities and others that might also be found in patients with CMT1A. All the patients showed electrophysiologic signs of underlying demyelinating polyneuropathy. Genetic study centered on detecting the deletion of 17p11.2 by segregation analysis with the polymorphic markers VAW409R3a (D17S122) and EW401HE (D17S61). Our results confirmed deletion at the CTM1A location of chromosome 17p11.2 in all 13 patients examined. These data suggest that the deletion of 17p11.2 plays a causal role in HNPP and that it is the most prevalent mutation in this disease; our findings constitute new evidence of the importance of the CMT1A/HNPP locus in the formation and control of peripheral myelin and in the ultimate functioning of peripheral nerves.

[The diagnosis and prevalence of locus CMT1A duplication in Charcot-Marie-Tooth disease type 1]

BACKGROUND

The Charcot-Marie-Tooth (CMT) disease or hereditary motor-sensitive neuropathy (HMSN) is the most frequent hereditary neuropathy. The demyelinated or type 1 form (CMT1) is the most frequently presented, commonly being of a dominant autosomic inheritance. CMT1 is heterogeneous genetically and the subjacent mutation found in most of the cases is a duplication of 1,500 kb in the CMT1A locus of chromosome 17p11.2. The aim of the present study was to determine the prevalence of CMT1A duplication in patients with CMT1 and evaluate its usefulness as a biological diagnostic marker.

METHODS

The study was carried out in a group of patients with HMSN who were not related, and were distributed according to the following diagnostic categories: CMT1 (n = 49), CMT2 (n = 9), untyped CMT (n = 11) and Déjérine-Sottas (DS) disease (n = 4). To detect three alleles confirming the presence of duplication the DNA of the patients was analyzed with four polymorph markers, VAW409R3a, RM11-GT, VAW412R3HEc and EW401HE localized in the CMT1A locus.

RESULTS

CMT1A duplication was found in 68.7% of the patients with CMT1 and in 27.2% of untyped CMT patients. None of the individuals in the CMT2 and DS categories showed duplication. Cases pertaining to families with dominant autosomic inheritance and genetically sporadic cases were confirmed to show a high prevalence of duplication, being of 83.3% and 85.7%, respectively.

CONCLUSIONS

Duplication of the CMT1A locus is the most prevalent mutation found in Charcot-Marie-Tooth type 1 disease. It is a specific mutation of this disease among the different forms of hereditary motor-sensitive neuropathy. This mutation is useful as a biological marker in the diagnosis of these neuropathies.

Subacute mucormycosis with secondary internal carotid occlusion: clinical and MR findings

A case of subacute mucormycosis with a cavernous sinus syndrome and internal carotid occlusion with survival after surgical and anfothericin B treatment in a patient with type II diabetes is reported. The RM images of this form of evolution of the infection by mucormycosis is also described. We suggest that a mucormycosis with subacute profile is possible in a well controlled patient with an underlying inmunosuppressive disorder, and that this form of mucormycosis should be considered in the differential diagnosis of the destructive lesions of the middle line, as a prompt identification of this disorder can improve the survival rate of patients.

Friedreich's ataxia: an epidemiological study in Valencia, Spain, based on consanguinity analysis

Epidemiological studies performed directly on the population show a prevalence of Friedreich's ataxia (FA) from 1 to 4.7 cases/100,000 inhabitants. An indirect epidemiological approach can be achieved using genetic methods like consanguinity studies to determine the frequency of a mutated gene and the incidence of certain diseases in the population. We obtained consanguinity data of a series of FA patients in Valencia, Spain and the figures on consanguinity in the general population that were estimated according to the Archive of Dispensations given by the Catholic church for consanguineous marriages. From these data, the frequency of the FA gene was calculated as 1/127. From these data, applying the Hardy-Weinberg principle, the frequency of the carriers was 1/64 and the incidence was 6.18/100,000 live births. Assuming a life expectancy of FA of 45 years, the prevalence was 3.83/100,000 inhabitants. These figures are in the same range as those obtained in population studies.

[Scleromyxedema associated with myopathy]

We describe a 45 year-old man, with scleromyxedema associated to systemic manifestations, including myopathy. After 6 years of dermatologic manifestations, muscular weakness, with proximal predominance resulting in incapacity, was established. Corticosteroids plus cyclophosphamide treatment suppressed muscular symptomatology, and a second biopsy was normal. The common association between scleromyxedema and myopathy and other systemic alterations suggest that this entity should probably be considered as a systemic disease instead as a skin disease.

[Disseminated encephalomyelitis. A study of 5 cases]

Five cases of acute disseminated encephalomyelitis (ADE) with a follow-up longer than 5 years are presented. The clinical picture, CT images, MR and laboratory tests, specially LCR and evoked potentials presented in a variable form. In two cases the symptoms were preceded by viral infection. The course was acute in one case while the other four evolved in a subacute form during weeks. In two patients a pseudotumoral pattern was observed in the CT and MR images leading to difficulties in the diagnosis. Clinical improvement was accompanied by a partial resolution of the lesions. Steroid treatment improved symptomatology in all the cases. Knowledge of this process may avoid the unnecessary practice of other, more aggressive tests.

[Genetic analysis of Friedreich's ataxia using polymorphic DNA markers]

Friedreich's ataxia (FA) is a progressive degenerative disease involving both central and peripheral nervous system. It is an autosomal recessive hereditary disorder, which begins around puberty and has an unknown genetic basis and biochemical defect. The recent mapping of FA locus in human chromosome 9 by means of the analysis of the molecular genetic linkage has permitted to evaluate FA genetics with polymorphic genetic markers (RFLPs) that are secreted linked with the FA gene. The normal and mutant allele secretion of FA was evaluated in ten Spanish families with one or two members with FA by means of several cloned probes (MCT112, DR47, D9S1 and HHH220), localized in chromosome 9 and strongly linked to FA gene, with the aim of achieving a predictive diagnosis of relatives in the pediatric age and to detect healthy carriers. In 9 out of 10 families some totally or partially informative RFLP were found. In 5 of 6 relatives in pediatric age the future development of the disease could be ruled out. By contrast, the carrier status could only be identified in three relatives. In a family with two affected children a genetic recombinant for D9S1 was found. Remarkably, one of them had a better clinical evolution and preserved tendon reflexes in lower limbs.

[The presence of oligoclonal bands in the cerebrospinal fluid in various neurologic diseases]

The polyacrylamide gel electrophoresis of spinal fluid from 488 patients suffering neurological diseases and from a control group are reviewed. One hundred and eleven cases (22.7%) showed oligoclonal bands (OB). The highest percentage of OB appeared in the group of patients with definite multiple sclerosis (84%), followed by those with probable multiple sclerosis (46%) and inflammatory infectious diseases (43%); the group of patients with a possible multiple sclerosis (7%), vascular malignancies (11%) and other diseases (4%) showed a lower incidence of OBs. No OBs were found in groups of patients with degenerative diseases, dementia or the control group. These results confirm the great usefulness of this test to support the diagnosis of multiple sclerosis, although it also shows that it is not a specific test so it should always be evaluated within a clinical context.