Claire-Marie Dhaenens

New syndromic form of benign hereditary chorea is associated with a deletion of TITF-1 and PAX-9 contiguous genes.

Benign hereditary chorea is a rare autosomal dominant disorder presenting with a childhood‐onset and slowly progressive chorea. The objective of this study was to describe the clinical and genetic features of 3 patients who developed childhood‐onset chorea. Three affected patients from three generations of a family with benign hereditary chorea associated with a multisystemic disorder of the basal ganglia, thyroid, lungs, salivary glands, bowels, and teeth. The TITF‐1 gene was screened by microsatellite analysis, gene sequencing, and fluorescence in situ hybridization. Genetic analysis revealed a novel 0.9‐Mb deletion on chromosome 14, which includes the TITF‐1 and PAX9 genes. We have identified a novel deletion responsible for a new syndrome of benign hereditary chorea, including symptoms of brain–thyroid–lung syndrome associated with bowels, salivary glands, and teeth disorders. Associated signs, sometimes of slight expression, remain of high interest for the clinical and genetic diagnosis of benign hereditary chorea.

A genetic variation in the ADORA2A gene modifies age at onset in Huntington's disease ☆

Based on the pathophysiological role of adenosine A(2A) receptors in HD, we have evaluated the association of the 1976C/T single-nucleotide polymorphism in the ADORA2A gene (rs5751876) with residual age at onset (AAO) in HD. The study population consisted of 791 unrelated patients belonging to the Huntington French Speaking Network. The variability in AAO attributable to the CAG repeats number was calculated by linear regression using the log (AAO) as the dependent variable, and the respective rs5751876 genotypes as independent variables. We show that the rs5751876 variant significantly influences the variability in AAO. The R(2) statistic rose slightly but significantly (p=0.019) when rs5751876 T/T genotype was added to the regression model. Patients harbouring T/T genotype have an earlier AAO of 3.8 years as compared to C/C genotype (p=0.02). Our data thus strengthens the pathophysiological role of A(2A) receptors in Huntingtons disease.

ETR-3 represses Tau exons 2/3 inclusion, a splicing event abnormally enhanced in myotonic dystrophy type I

Altered splicing of transcripts, including the insulin receptor (IR) and the cardiac troponin (cTNT), is a key feature of myotonic dystrophy type I (DM1). CELF and MBNL splicing factor members regulate the splicing of those transcripts. We have previously described an alteration of Tau exon 2 splicing in DM1 brain, resulting in the favored exclusion of exon 2. However, the factors required for alternative splicing of Tau exon 2 remain undetermined. Here we report a decreased expression of CELF family member and MBNL transcripts in DM1 brains as assessed by RT‐PCR. By using cellular models with a control‐ or DM1‐like splicing pattern of Tau transcripts, we demonstrate that ETR‐3 promotes selectively the exclusion of Tau exon 2. These results together with the analysis of Tau exon 6 and IR exon 11 splicing in brain, muscle, and cell models suggest that DM1 splicing alteration of several transcripts involves various factors.

Tau as a biomarker of neurodegenerative diseases

The microtubule-associated protein Tau is mainly expressed in neurons of the CNS and is crucial in axonal maintenance and axonal transport. The rationale for Tau as a biomarker of neurodegenerative diseases is that it is a major component of abnormal intraneuronal aggregates observed in numerous tauopathies, including Alzheimers disease. The molecular diversity of Tau is very useful when analyzing it in the brain or in the peripheral fluids. Immunohistochemical and biochemical characterization of Tau aggregates in the brain allows the postmortem classification and differential diagnosis of tauopathies. As peripheral biomarkers of Alzheimers disease in the cerebrospinal fluid, Tau proteins are now validated for diagnosis and predictive purposes. For the future, the detailed characterization of Tau in the brain and in peripheral fluids will lead to novel promising biomarkers for differential diagnosis of dementia and monitoring of therapeutics.

Analysis of Exonic Regions Involved in Nuclear Localization, Splicing Activity, and Dimerization of Muscleblind-like-1 Isoforms

Muscleblind-like-1 (MBNL1) is a splicing regulatory factor controlling the fetal-to-adult alternative splicing transitions during vertebrate muscle development. Its capture by nuclear CUG expansions is one major cause for type 1 myotonic dystrophy (DM1). Alternative splicing produces MBNL1 isoforms that differ by the presence or absence of the exonic regions 3, 5, and 7. To understand better their respective roles and the consequences of the deregulation of their expression in DM1, here we studied the respective roles of MBNL1 alternative and constitutive exons. By combining genetics, molecular and cellular approaches, we found that (i) the exon 5 and 6 regions are both needed to control the nuclear localization of MBNL1; (ii) the exon 3 region strongly enhances the affinity of MBNL1 for its pre-mRNA target sites; (iii) the exon 3 and 6 regions are both required for the splicing regulatory activity, and this function is not enhanced by an exclusive nuclear localization of MBNL1; and finally (iv) the exon 7 region enhances MBNL1-MBNL1 dimerization properties. Consequently, the abnormally high inclusion of the exon 5 and 7 regions in DM1 is expected to enhance the potential of MBNL1 of being sequestered with nuclear CUG expansions, which provides new insight into DM1 pathophysiology.

Brain pathology in myotonic dystrophy: when tauopathy meets spliceopathy and RNAopathy

Myotonic dystrophy (DM) of type 1 and 2 (DM1 and DM2) are inherited autosomal dominant diseases caused by dynamic and unstable expanded microsatellite sequences (CTG and CCTG, respectively) in the non-coding regions of the genes DMPK and ZNF9, respectively. These mutations result in the intranuclear accumulation of mutated transcripts and the mis-splicing of numerous transcripts. This so-called RNA gain of toxic function is the main feature of an emerging group of pathologies known as RNAopathies. Interestingly, in addition to these RNA inclusions, called foci, the presence of neurofibrillary tangles (NFT) in patient brains also distinguishes DM as a tauopathy. Tauopathies are a group of nearly 30 neurodegenerative diseases that are characterized by intraneuronal protein aggregates of the microtubule-associated protein Tau (MAPT) in patient brains. Furthermore, a number of neurodegenerative diseases involve the dysregulation of splicing regulating factors and have been characterized as spliceopathies. Thus, myotonic dystrophies are pathologies resulting from the interplay among RNAopathy, spliceopathy, and tauopathy. This review will describe how these processes contribute to neurodegeneration. We will first focus on the tauopathy associated with DM1, including clinical symptoms, brain histology, and molecular mechanisms. We will also discuss the features of DM1 that are shared by other tauopathies and, consequently, might participate in the development of a tauopathy. Moreover, we will discuss the determinants common to both RNAopathies and spliceopathies that could interfere with tau-related neurodegeneration.

Systematic Screening of BEST1 and PRPH2 in Juvenile and Adult Vitelliform Macular Dystrophies: A Rationale for Molecular Analysis

PURPOSE To evaluate a genetic approach of BEST1 and PRPH2 screening according to age of onset, family history, and Arden ratio in patients with juvenile vitelliform macular dystrophy (VMD2) or adult-onset vitelliform macular dystrophy (AVMD), which are characterized by autofluorescent deposits. DESIGN Clinical, electrophysiologic, and molecular retrospective study. PARTICIPANTS The database of a clinic specialized in genetic sensory diseases was screened for patients with macular vitelliform dystrophy. Patients with an age of onset less than 40 years were included in the VMD2 group (25 unrelated patients), and patients with an age of onset more than 40 years were included in the AVMD group (19 unrelated patients). METHODS Clinical, fundus photography, and electro-oculogram (EOG) findings were reviewed. Mutation screening of BEST1 and PRPH2 genes was systematically performed. MAIN OUTCOME MEASURES Relevance of age of onset, family history, and Arden ratio were reviewed. RESULTS Patients with VMD2 carried a BEST1 mutation in 60% of the cases. Seven novel mutations in BEST1 (p.V9L, p.F80V, p.I73V, p.R130S, pF298C, pD302A, and p.179delN) were found. Patients with VMD2 with a positive family history or a reduced Arden ratio carried a BEST1 mutation in 70.5% of cases and in 83% if both criteria were fulfilled. Patients with AVMD carried a PRPH2 mutation in 10.5% of cases and did not carry a BEST1 mutation. The probability of finding a PRPH2 mutation increased in the case of a family history (2/5 patients). Electro-oculogram was normal in 3 of 15 patients with BEST1 mutations and reduced in the 3 patients with PRPH2 mutations. CONCLUSIONS Age of onset is a major criterion to distinguish VMD2 from AVMD. Electro-oculogram is not as relevant because decreased or normal Arden ratios have been associated with mutations in both genes and diseases. A positive family history increased the probability of finding a mutation. BEST1 screening should be recommended to patients with an age of onset less than 40 years, and PRPH2 screening should be recommended to patients with an age of onset more than 40 years. For an onset between 30 and 40 years, PRPH2 can be screened if no mutation has been detected in BEST1. FINANCIAL DISCLOSURE(S) The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Mis-splicing of Tau exon 10 in myotonic dystrophy type 1 is reproduced by overexpression of CELF2 but not by MBNL1 silencing

Tau is the proteinaceous component of intraneuronal aggregates common to neurodegenerative diseases called Tauopathies, including myotonic dystrophy type 1. In myotonic dystrophy type 1, the presence of microtubule-associated protein Tau aggregates is associated with a mis-splicing of Tau. A toxic gain-of-function at the ribonucleic acid level is a major etiological factor responsible for the mis-splicing of several transcripts in myotonic dystrophy type 1. These are probably the consequence of a loss of muscleblind-like 1 (MBNL1) function or gain of CUGBP1 and ETR3-like factor 1 (CELF1) splicing function. Whether these two dysfunctions occur together or separately and whether all mis-splicing events in myotonic dystrophy type 1 brain result from one or both of these dysfunctions remains unknown. Here, we analyzed the splicing of Tau exons 2 and 10 in the brain of myotonic dystrophy type 1 patients. Two myotonic dystrophy type 1 patients showed a mis-splicing of exon 10 whereas exon 2-inclusion was reduced in all myotonic dystrophy type 1 patients. In order to determine the potential factors responsible for exon 10 mis-splicing, we studied the effect of the splicing factors muscleblind-like 1 (MBNL1), CUGBP1 and ETR3-like factor 1 (CELF1), CUGBP1 and ETR3-like factor 2 (CELF2), and CUGBP1 and ETR3-like factor 4 (CELF4) or a dominant-negative CUGBP1 and ETR-3 like factor (CELF) factor on Tau exon 10 splicing by ectopic expression or siRNA. Interestingly, the inclusion of Tau exon 10 is reduced by CUGBP1 and ETR3-like factor 2 (CELF2) whereas it is insensitive to the loss-of-function of muscleblind-like 1 (MBNL1), CUGBP1 and ETR3-like factor 1 (CELF1) gain-of-function, or a dominant-negative of CUGBP1 and ETR-3 like factor (CELF) factor. Moreover, we observed an increased expression of CUGBP1 and ETR3-like factor 2 (CELF2) only in the brain of myotonic dystrophy type 1 patients with a mis-splicing of exon 10. Taken together, our results indicate the occurrence of a mis-splicing event in myotonic dystrophy type 1 that is induced neither by a loss of muscleblind-like 1 (MBNL1) function nor by a gain of CUGBP1 and ETR3-like factor 1 (CELF1) function but is rather associated to CUGBP1 and ETR3-like factor 2 (CELF2) gain-of-function.

Microtubule-associated protein tau gene: a risk factor in human neurodegenerative diseases

Tau is a microtubule-associated protein mainly expressed in neurons of central nervous system, which is crucial in the maintenance of these cells. It has a central role in the polymerization and stabilization of microtubules and in the traffic of organelles along axons and dendrites. Aggregates of hyperphosphorylated forms of tau protein participate in the formation of neurofibrillary tangles, which characterize numerous neurodegenerative disorders named tauopathies. The analysis of tau gene and the study of familial cases of tauopathies have led to the discovery of tau gene mutations that cause inherited dementia designated as Frontotemporal dementia (FTD) with parkinsonism linked to chromosome 17 (FTDP-17). However, these familial cases remain rare compared to the sporadic tauopathies, the later involving both genetic and environmental etiologic factors. As tau pathology represents a primary pathogenic event in various neurodegenerative diseases, the hypothesis that tau genotype could influence the development of these diseases was tested by several groups. This review summarizes advances in the molecular genetics of the tau gene, as well as recent studies addressing the disease incidence of novel tau polymorphisms in different neurodegenerative diseases. Hopefully, the identification of several genetic defects of the tau gene will be helpful in improving our understanding of the role of tau protein in the pathogenesis of various neurodegenerative diseases.

Relative frequencies of inherited retinal dystrophies and optic neuropathies in Southern France: assessment of 21-year data management.

ABSTRACT Purpose: Inherited retinal dystrophies (IRDs) and inherited optic neuropathies (IONs) are rare diseases defined by specific clinical and molecular features. The relative prevalence of these conditions was determined in Southern France. Methods: Patients recruited from a specialized outpatient clinic over a 21-year period underwent extensive clinical investigations and 107 genes were screened by polymerase chain reaction/sequencing. Results: There were 1957 IRD cases (1481 families) distributed in 70% of pigmentary retinopathy cases (56% non-syndromic, 14% syndromic), 20% maculopathies and 7% stationary conditions. Patients with retinitis pigmentosa were the most frequent (47%) followed by Usher syndrome (10.8%). Among non-syndromic pigmentary retinopathy patients, 84% had rod-cone dystrophy, 8% cone-rod dystrophy and 5% Leber congenital amaurosis. Macular dystrophies were encountered in 398 cases (30% had Stargardt disease and 11% had Best disease). There were 184 ION cases (127 families) distributed in 51% with dominant optic neuropathies, 33% with recessive/sporadic forms and 16% with Leber hereditary optic neuropathy. Positive molecular results were obtained in 417/609 families with IRDs (68.5%) and in 27/58 with IONs (46.5%). The sequencing of 5 genes (ABCA4, USH2A, MYO7A, RPGR and PRPH2) provided a positive molecular result in 48% of 417 families with IRDs. Except for autosomal retinitis pigmentosa, in which less than half the families had positive molecular results, about 75% of families with other forms of retinal conditions had a positive molecular diagnosis. Conclusions: Although gene discovery considerably improved molecular diagnosis in many subgroups of IRDs and IONs, retinitis pigmentosa, accounting for almost half of IRDs, remains only partly molecularly defined.