Copy Number Variant Analysis of Spinocerebellar Ataxia Genes in a Cohort of Dutch Patients With Cerebellar Ataxia.

Background and Objectives: The spinocerebellar ataxias (SCAs) are a genetically heterogeneous group of neurodegenerative disorders generally caused by single nucleotide variants (SNVs) or indels in coding regions or by repeat expansions in coding and noncoding regions of SCA genes. Copy number variants (CNVs) have now also been reported for 3 genes-ITPR1, FGF14, and SPTBN2-but not all SCA genes have been screened for CNVs as the underlying cause of the disease in patients. In this study, we aim to assess the prevalence of CNVs encompassing 36 known SCA genes. Methods: A cohort of patients with cerebellar ataxia who were referred to the University Medical Center Groningen for SCA genetic diagnostics was selected for this study. Genome-wide single nucleotide polymorphism (SNP) genotyping was performed using the Infinium Global Screening Array. Following data processing, genotyping data were uploaded into NxClinical software to perform CNV analysis per patient and to visualize identified CNVs in 36 genes with allocated SCA symbols. The clinical relevance of detected CNVs was determined using evidence from studies based on PubMed literature searches for similar CNVs and phenotypic features. Results: Of the 338 patients with cerebellar ataxia, we identified putative clinically relevant CNV deletions in 3 patients: an identical deletion encompassing ITPR1 in 2 patients, who turned out to be related, and a deletion involving PPP2R2B in another patient. Although the CNV deletion in ITPR1 was clearly the underlying cause of SCA15 in the 2 related patients, the clinical significance of the deletion in PPP2R2B remained unknown. Discussion: We showed that CNVs detectable with the limited resolution of SNP array are a very rare cause of SCA. Nevertheless, we suggest adding CNV analysis alongside SNV analysis to SCA gene diagnostics using next-generation sequencing approaches, at least for ITPR1, to improve the genetic diagnostics for patients.

Prevalence of intronic repeat expansions in RFC1 in Dutch patients with CANVAS and adult-onset ataxia.

Recently, an intronic biallelic (AAGGG)n repeat expansion in RFC1 was shown to be a cause of CANVAS and adult-onset ataxia in multiple populations. As the prevalence of the RFC1 repeat expansion in Dutch cases was unknown, we retrospectively tested 9 putative CANVAS cases and two independent cohorts (A and B) of 395 and 222 adult-onset ataxia cases, respectively, using the previously published protocol and, for the first time optical genome mapping to determine the size of the expanded RFC1 repeat. We identified the biallelic (AAGGG)n repeat expansion in 5/9 (55%) putative CANVAS patients and in 10/617 (1.6%; cohorts A + B) adult-onset ataxia patients. In addition to the AAGGG repeat motif, we observed a putative GAAGG repeat motif in the repeat expansion with unknown significance in two adult-onset ataxia patients. All the expanded (AAGGG)n repeats identified were in the range of 800-1299 repeat units. The intronic biallelic RFC1 repeat expansion thus explains a number of the Dutch adult-onset ataxia cases that display the main clinical features of CANVAS, and particularly when ataxia is combined with neuropathy. The yield of screening for RFC1 expansions in unselected cohorts is relatively low. To increase the current diagnostic yield in ataxia patients, we suggest adding RFC1 screening to the genetic diagnostic workflow by using advanced techniques that attain long fragments.

Feasibility of Follow-Up Studies and Reclassification in Spinocerebellar Ataxia Gene Variants of Unknown Significance.

Spinocerebellar ataxia (SCA) is a heterogeneous group of neurodegenerative disorders with autosomal dominant inheritance. Genetic testing for SCA leads to diagnosis, prognosis and risk assessment for patients and their family members. While advances in sequencing and computing technologies have provided researchers with a rapid expansion in the genetic test content that can be used to unravel the genetic causes that underlie diseases, the large number of variants with unknown significance (VUSes) detected represent challenges. To minimize the proportion of VUSes, follow-up studies are needed to aid in their reclassification as either (likely) pathogenic or (likely) benign variants. In this study, we addressed the challenge of prioritizing VUSes for follow-up using (a combination of) variant segregation studies, 3D protein modeling, in vitro splicing assays and functional assays. Of the 39 VUSes prioritized for further analysis, 13 were eligible for follow up. We were able to reclassify 4 of these VUSes to LP, increasing the molecular diagnostic yield by 1.1%. Reclassification of VUSes remains difficult due to limited possibilities for performing variant segregation studies in the classification process and the limited availability of routine functional tests.

Clinical, genetic, and histological features of centronuclear myopathy in the Netherlands.

Centronuclear myopathy (CNM) is a genetically heterogeneous congenital myopathy characterized by muscle weakness, atrophy, and variable degrees of cardiorespiratory involvement. The clinical severity is largely explained by genotype (DNM2, MTM1, RYR1, BIN1, TTN, and other rarer genetic backgrounds), specific mutation(s), and age of the patient. The histopathological hallmark of CNM is the presence of internal centralized nuclei on muscle biopsy. Information on the phenotypical spectrum, subtype prevalence, and phenotype-genotype correlations is limited. To characterize CNM more comprehensively, we retrospectively assessed a national cohort of 48 CNM patients (mean age = 32 ± 24 years, range 0-80, 54% males) from the Netherlands clinically, histologically, and genetically. All information was extracted from entries in the patient's medical records, between 2000 and 2020. Frequent clinical features in addition to muscle weakness and hypotonia were fatigue and exercise intolerance in more mildly affected cases. Genetic analysis showed variants in four genes (18 DNM2, 14 MTM1, 9 RYR1, and 7 BIN1), including 16 novel variants. In addition to central nuclei, histologic examination revealed a large variability of myopathic features in the different genotypes. The identification and characterization of these patients contribute to trial readiness.

Biallelic loss of function variants in SYT2 cause a treatable congenital onset presynaptic myasthenic syndrome.

Synaptotagmins are integral synaptic vesicle membrane proteins that function as calcium sensors and regulate neurotransmitter release at the presynaptic nerve terminal. Synaptotagmin-2 (SYT2), is the major isoform expressed at the neuromuscular junction. Recently, dominant missense variants in SYT2 have been reported as a rare cause of distal motor neuropathy and myasthenic syndrome, manifesting with stable or slowly progressive distal weakness of variable severity along with presynaptic NMJ impairment. These variants are thought to have a dominant-negative effect on synaptic vesicle exocytosis, although the precise pathomechanism remains to be elucidated. Here we report seven patients of five families, with biallelic loss of function variants in SYT2, clinically manifesting with a remarkably consistent phenotype of severe congenital onset hypotonia and weakness, with variable degrees of respiratory involvement. Electrodiagnostic findings were consistent with a presynaptic congenital myasthenic syndrome (CMS) in some. Treatment with an acetylcholinesterase inhibitor pursued in three patients showed clinical improvement with increased strength and function. This series further establishes SYT2 as a CMS-disease gene and expands its clinical and genetic spectrum to include recessive loss-of-function variants, manifesting as a severe congenital onset presynaptic CMS with potential treatment implications.

Predictive genetic testing in Huntington's disease: should a neurologist be involved?

International guidelines on Huntington's Disease recommend neurological examination in the predictive testing trajectory. Experiences and personal wishes of persons at risk of Huntington's Disease regarding this topic have never been evaluated. The objective was to provide an overview of the experiences of Dutch at-risk persons, opting for predictive testing, in consulting a neurologist before and after DNA analysis. Persons who were counseled in four Dutch clinics between 2017 and 2019 were retrospectively or prospectively approached for a questionnaire which listed topics as experiences with consultation and personal wishes. From 71 participants, 44 participants visited a neurologist. 41 participants indicated their visit to a neurologist as positive (93.2%). The majority of participants (n = 59) desired consulting a neurologist. Thirty-two participants indicated consultation shortly after (Desired After Group) and twenty-seven before DNA analysis (Desired Before Group) as personal wish. The Desired Before Group consisted of a significantly higher number of participants who actually consulted a neurologist before predictive testing (n = 26) compared with the number of participants who actually consulted a neurologist after DNA analysis in the Desired After Group (n = 11) (p < 0.001). The Desired After Group (n = 19) had a significantly higher number of Huntington's disease gene expansion carriers compared with the Desired Before Group (n = 5) (p 0.003). Participants are content with consultation. However, persons without the gene expansion still feel the need to get in touch with a neurologist. Therefore, offering a consultation with a neurologist before DNA analysis might be beneficial for all.

Paediatric motor phenotypes in early-onset ataxia, developmental coordination disorder, and central hypotonia.

AIMS: To investigate the accuracy of phenotypic early-onset ataxia (EOA) recognition among developmental conditions, including developmental coordination disorder (DCD) and hypotonia of central nervous system origin, and the effect of scientifically validated EOA features on changing phenotypic consensus. METHOD: We included 32 children (4-17y) diagnosed with EOA (n=11), DCD (n=10), and central hypotonia (n=11). Three paediatric neurologists independently assessed videotaped motor behaviour phenotypically and quantitatively (using the Scale for Assessment and Rating of Ataxia [SARA]). We determined: (1) phenotypic interobserver agreement and phenotypic homogeneity (percentage of phenotypes with full consensus by all three observers according to the underlying diagnosis); (2) SARA (sub)score profiles; and (3) the effect of three scientifically validated EOA features on phenotypic consensus. RESULTS: Phenotypic homogeneity occurred in 8 out of 11, 2 out of 10, and 1 out of 11 patients with EOA, DCD, and central hypotonia respectively. Homogeneous phenotypic discrimination of EOA from DCD and central hypotonia occurred in 16 out of 21 and 22 out of 22 patients respectively. Inhomogeneously discriminated EOA and DCD phenotypes (5 out of 21) revealed overlapping SARA scores with different SARA subscore profiles. After phenotypic reassessment with scientifically validated EOA features, phenotypic homogeneity changed from 16 to 18 patients. INTERPRETATION: In contrast to complete distinction between EOA and central hypotonia, the paediatric motor phenotype did not reliably distinguish between EOA and DCD. Reassessment with scientifically validated EOA features could contribute to a higher phenotypic consensus. Early-onset ataxia (EOA) and central hypotonia motor phenotypes were reliably distinguished. EOA and developmental coordination disorder (DCD) motor phenotypes were not reliably distinguished. The EOA and DCD phenotypes have different profiles of the Scale for Assessment and Rating of Ataxia.

FENOTIPOS PEDIÁTRICOS MOTORES EN ATAXIA DE INICIO TEMPRANO, TRASTORNO DEL DESARROLLO DE LA COORDINACIÓN E HIPOTONÍA DE ORIGEN CENTRAL: OBJETIVOS: Investigar la precisión del reconocimiento fenotípico de ataxia de inicio temprano (EOA) con respecto a trastornos del desarrollo, incluido el trastorno del desarrollo de la coordinación (TDC) y la hipotonía de origen central. Investigar el efecto de las características científicamente validadas de EOA sobre el consenso fenotípico entre los evaluadores. MÉTODO: Se incluyeron 32 niños (4-17 años) diagnosticados con EOA (n = 11), TDC (n = 10) e hipotonía central (n = 11). Tres neurólogos pediátricos evaluaron de forma independiente el comportamiento motor grabado en video en cuanto a las características fenotípica y cuantitativa (utilizando la Escala de evaluación y calificación de la ataxia [SARA]). Determinamos: (1) coincidencia fenotípica entre los observadores y homogeneidad fenotípica (porcentaje de fenotipos con consenso total de los tres observadores según el diagnóstico subyacente), (2) perfiles de (sub)puntajes en el SARA y (3) el efecto sobre el consenso fenotípico de tres características de EOA validadas científicamente. RESULTADOS: La homogeneidad fenotípica ocurrió en 8 de 11, 2 de 10 y 1 de 11 pacientes con EOA, DCD e hipotonía central, respectivamente. La discriminación fenotípica homogénea de EOA con respecto a TDC e hipotonía central se produjo en 16 de 21 y 22 de 22 pacientes, respectivamente. Los fenotipos EOA y TDC que no fueron discriminados de manera homogénea por los observadores (5 de 21) revelaron superposición en los puntajes del SARA con diferentes perfiles en los subpuntajes del SARA. Después de una reevaluación fenotípica con características EOA científicamente validadas, la homogeneidad fenotípica cambió de 16 a 18 pacientes. INTERPRETACIÓN: En contraste con la distinción completa entre EOA e hipotonía central, el fenotipo motor pediátrico no distinguió confiablemente entre EOA y TDC. La evaluación en base a características EOA científicamente validadas podría contribuir a un mayor consenso fenotípico.

FENÓTIPOS MOTORES PEDIÁTRICOS NA ATAXIA DE INÍCIO PRECOCE, TRANSTORNO DO DESENVOLVIMENTO DA COORDENACÃO, E HIPOTONIA CENTRAL: OBJETIVOS: Investigar a acurácia do reconhecimento fenotípico da ataxia de início precoce (AIP) entre condições desenvolvimentais, incluindo o transtorno do desenvolvimento da coordenação (TDC) e a hipotonia de origem no sistema nervoso central, e o efeito de aspectos cientificamente validados da AIP na modificação do consenso fenotípico. MÉTODO: Incluímos 32 crianças (4-17a) diagnosticadas com AIP (n=11), TDC (n=10), e hipotonia central (n=11). Três neurologistas pediátricos avaliaram de maneira independente por meio de vídeo o comportamento motor tanto por meio do fenótiopo quanto quantitativamente (usando a Escala para Avaliação e Pontuação da Ataxia) [EAPA]). Determinamos: (1) a concordânica fenotípica inter-observadores e a homogeneidade fenotípica (porcentagem de fenótipos com consenso completo pelos três observadores de acordo com o diagnóstico de base, (2) perfis segundo os (sub)escores da EAPA, e (3) o efeito de três aspectos cientificamente validados da AIP sobre o consenso fenotípico. RESULTADOS: A homogeneidade fenotípica ocorreu em 8 entre 12, 2 entre 10, e 1 entre 11 pacientes com AIP, TDC, e hipotonia central, respectivamente. A discriminação fenotípica homogênea da AIP com relação ao TDC e hipotonia central ocorreu em 16 entre 21 e 21 entre 22 pacientes, respectivamente. A discriminação não homogêna dos fenótipos AIP e TDC (5 em 21) revelou escores da EAPA que sobrepõem com diferentes perfis de subescores da EAPA. Após reavaliação fenotípica com aspectos cientificamente validados da AIP, a homogeneidade fenotípica mudou de 16 para 18 pacientes. INTERPRETAÇÃO: Em contraste com a completa distinção entre AIP e hipotonia central, o fenótipo motor pediátrico não distinguiu confiavelmente entre AIP e TDC. A reavaliação com aspectos cientificamente valiaddos da AIP pode contribuir para um maior consenso fenotípica. contrast to complete distinction between EOA and central hypotonia, the paediatric motor phenotype did not reliably distinguish between EOA and DCD. eassessment with scientifically validated EOA features could contribute to a higher phenotypic consensus.

Panel-Based Exome Sequencing for Neuromuscular Disorders as a Diagnostic Service.

BACKGROUND: Neuromuscular disorders (NMDs) are clinically and genetically heterogeneous. Accurate molecular genetic diagnosis can improve clinical management, provides appropriate genetic counseling and testing of relatives, and allows potential therapeutic trials. OBJECTIVE: To establish the clinical utility of panel-based whole exome sequencing (WES) in NMDs in a population with children and adults with various neuromuscular symptoms. METHODS: Clinical exome sequencing, followed by diagnostic interpretation of variants in genes associated with NMDs, was performed in a cohort of 396 patients suspected of having a genetic cause with a variable age of onset, neuromuscular phenotype, and inheritance pattern. Many had previously undergone targeted gene testing without results. RESULTS: Disease-causing variants were identified in 75/396 patients (19%), with variants in the three COL6-genes (COL6A1, COL6A2 and COL6A3) as the most common cause of the identified muscle disorder, followed by variants in the RYR1 gene. Together, these four genes account for almost 25% of cases in whom a definite genetic cause was identified. Furthermore, likely pathogenic variants and/or variants of uncertain significance were identified in 95 of the patients (24%), in whom functional and/or segregation analysis should be used to confirm or reject the pathogenicity. In 18% of the cases with a disease-causing variant of which we received additional clinical information, we identified a genetic cause in genes of which the associated phenotypes did not match that of the patients. Hence, the advantage of panel-based WES is its unbiased approach. CONCLUSION: Whole exome sequencing, followed by filtering for NMD genes, offers an unbiased approach for the genetic diagnostics of NMD patients. This approach could be used as a first-tier test in neuromuscular disorders with a high suspicion of a genetic cause. With uncertain results, functional testing and segregation analysis are needed to complete the evidence.

Crossing barriers: a multidisciplinary approach to children and adults with young-onset movement disorders.

BACKGROUND: Diagnosis of less common young-onset movement disorders is often challenging, requiring a broad spectrum of skills of clinicians regarding phenotyping, normal and abnormal development and the wide range of possible acquired and genetic etiologies. This complexity often leads to considerable diagnostic delays, paralleled by uncertainty for patients and their families. Therefore, we hypothesized that these patients might benefit from a multidisciplinary approach. We report on the first 100 young-onset movement disorders patients who visited our multidisciplinary outpatient clinic. METHODS: Clinical data were obtained from the medical records of patients with disease-onset before age 18 years. We investigated whether the multidisciplinary team, consisting of a movement disorder specialist, pediatric neurologist, pediatrician for inborn errors of metabolism and clinical geneticist, revised the movement disorder classification, etiological diagnosis, and/or treatment. RESULTS: The 100 referred patients (56 males) had a mean age of 12.5 ± 6.3 years and mean disease duration of 9.2 ± 6.3 years. Movement disorder classification was revised in 58/100 patients. Particularly dystonia and myoclonus were recognized frequently and supported by neurophysiological testing in 24/29 patients. Etiological diagnoses were made in 24/71 (34%) formerly undiagnosed patients, predominantly in the genetic domain. Treatment strategy was adjusted in 60 patients, of whom 43 (72%) reported a subjective positive effect. CONCLUSIONS: This exploratory study demonstrates that a dedicated tertiary multidisciplinary approach to complex young-onset movement disorders may facilitate phenotyping and improve recognition of rare disorders, with a high diagnostic yield and minimal diagnostic delay. Future studies are needed to investigate the cost-benefit ratio of a multidisciplinary approach in comparison to regular subspecialty care.

Predictive testing of minors for Huntington's disease: The UK and Netherlands experiences.

A consistent feature of predictive testing guidelines for Huntington's disease (HD) is the recommendation not to undertake predictive tests on those < 18 years. Exceptions are made but the extent of, and reasons for, deviation from the guidelines are unknown. The UK Huntington's Prediction Consortium has collected data annually on predictive tests undertaken from the 23 UK genetic centers. DNA analysis for HD in the Netherlands is centralized in the Laboratory for Diagnostic Genome Analysis in Leiden. In the UK, 60 tests were performed on minors between 1994 and 2015 representing 0.63% of the total number of tests performed. In the Netherlands, 23 tests were performed on minors between 1997 and 2016. The majority of the tests were performed on those aged 16 and 17 years for both countries (23% and 57% for the UK, and 26% and 57% for the Netherlands). Data on the reasons for testing were identified for 36 UK and 22 Netherlands cases and included: close to the age of 18 years, pregnancy, currently in local authority care and likely to have less support available after 18 years, person never having the capacity to consent and other miscellaneous reasons. This study documents the extent of HD testing of minors in the UK and the Netherlands and suggests that, in general, the recommendation is being followed. We provide some empirical evidence as to reasons why clinicians have departed from the recommendation. We do not advise changing the recommendation but suggest that testing of minors continues to be monitored.

Exome sequencing and network analysis identifies shared mechanisms underlying spinocerebellar ataxia.

The autosomal dominant cerebellar ataxias, referred to as spinocerebellar ataxias in genetic nomenclature, are a rare group of progressive neurodegenerative disorders characterized by loss of balance and coordination. Despite the identification of numerous disease genes, a substantial number of cases still remain without a genetic diagnosis. Here, we report five novel spinocerebellar ataxia genes, FAT2, PLD3, KIF26B, EP300, and FAT1, identified through a combination of exome sequencing in genetically undiagnosed families and targeted resequencing of exome candidates in a cohort of singletons. We validated almost all genes genetically, assessed damaging effects of the gene variants in cell models and further consolidated a role for several of these genes in the aetiology of spinocerebellar ataxia through network analysis. Our work links spinocerebellar ataxia to alterations in synaptic transmission and transcription regulation, and identifies these as the main shared mechanisms underlying the genetically diverse spinocerebellar ataxia types.

A post hoc study on gene panel analysis for the diagnosis of dystonia.

BACKGROUND: Genetic disorders causing dystonia show great heterogeneity. Recent studies have suggested that next-generation sequencing techniques such as gene panel analysis can be effective in diagnosing heterogeneous conditions. The objective of this study was to investigate whether dystonia patients with a suspected genetic cause could benefit from the use of gene panel analysis. METHODS: In this post hoc study, we describe gene panel analysis results of 61 dystonia patients (mean age, 31 years; 72% young onset) in our tertiary referral center. The panel covered 94 dystonia-associated genes. As comparison with a historic cohort was not possible because of the rapidly growing list of dystonia genes, we compared the diagnostic workup with and without gene panel analysis in the same patients. The workup without gene panel analysis (control group) included theoretical diagnostic strategies formulated by independent experts in the field, based on detailed case descriptions. The primary outcome measure was diagnostic yield; secondary measures were cost and duration of diagnostic workup. RESULTS: Workup with gene panel analysis led to a confirmed molecular diagnosis in 14.8%, versus 7.4% in the control group (P = 0.096). In the control group, on average 3 genes/case were requested. The mean costs were lower in the gene panel analysis group (€1822/case) than in the controls (€2660/case). The duration of the workup was considerably shorter with gene panel analysis (28 vs 102 days). CONCLUSIONS: Gene panel analysis facilitates molecular diagnosis in complex cases of dystonia, with a good diagnostic yield (14.8%), a quicker diagnostic workup, and lower costs, representing a major improvement for patients and their families. © 2016 International Parkinson and Movement Disorder Society.

Dystonia-deafness syndrome caused by a ß-actin gene mutation and response to deep brain stimulation.

INTRODUCTION: Dystonia-deafness syndrome is a distinct clinical presentation within the dystonia-spectrum. Although several genetic and acquired causes have been reported, etiology remains unknown in the majority of patients. OBJECTIVES: To describe two patients with dystonia-deafness syndrome due to a beta-actin gene mutation. METHODS: We report on disease course, genetic testing, and management of 2 patients, mother and daughter, presenting with dystonia-deafness syndrome. RESULTS: After exclusion of known dystonia-deafness syndrome causes, whole-exome sequencing revealed a beta-actin gene mutation (p.Arg183Trp) in both patients. Although beta-actin gene mutations are generally associated with developmental Baraitser-Winter syndrome, dystonia-deafness syndrome has been reported once in identical twin brothers. Bilateral GPi-DBS led to a significant decrease of dystonia and regain of independency in our patients. CONCLUSION: The p.Arg183Trp mutation in the beta-actin gene is associated with the clinical presentation of dystonia-deafness syndrome, even with only minimal or no developmental abnormalities of Baraitser-Winter syndrome. GPi-DBS should be considered to ameliorate the invalidating dystonia in these patients. © 2016 International Parkinson and Movement Disorder Society.

Functional analysis helps to define KCNC3 mutational spectrum in Dutch ataxia cases.

Spinocerebellar ataxia type 13 (SCA13) is an autosomal dominantly inherited neurodegenerative disorder of the cerebellum caused by mutations in the voltage gated potassium channel KCNC3. To identify novel pathogenic SCA13 mutations in KCNC3 and to gain insights into the disease prevalence in the Netherlands, we sequenced the entire coding region of KCNC3 in 848 Dutch cerebellar ataxia patients with familial or sporadic origin. We evaluated the pathogenicity of the identified variants by co-segregation analysis and in silico prediction followed by biochemical and electrophysiological studies. We identified 19 variants in KCNC3 including 2 non-coding, 11 missense and 6 synonymous variants. Two missense variants did not co-segregate with the disease and were excluded as potentially disease-causing mutations. We also identified the previously reported p.R420H and p.R423H mutations in our cohort. Of the remaining 7 missense variants, functional analysis revealed that 2 missense variants shifted Kv3.3 channel activation to more negative voltages. These variations were associated with early disease onset and mild intellectual disability. Additionally, one other missense variant shifted channel activation to more positive voltages and was associated with spastic ataxic gait. Whereas, the remaining missense variants did not change any of the channel characteristics. Of these three functional variants, only one variant was in silico predicted to be damaging and segregated with disease. The other two variants were in silico predicted to be benign and co-segregation analysis was not optimal or could only be partially confirmed. Therefore, we conclude that we have identified at least one novel pathogenic mutation in KCNC3 that cause SCA13 and two additionally potential SCA13 mutations. This leads to an estimate of SCA13 prevalence in the Netherlands to be between 0.6% and 1.3%.

Dystonia in children and adolescents: a systematic review and a new diagnostic algorithm.

Early aetiological diagnosis is of paramount importance for childhood dystonia because some of the possible underlying conditions are treatable. Numerous genetic and non-genetic causes have been reported, and diagnostic workup is often challenging, time consuming and costly. Recently, a paradigm shift has occurred in molecular genetic diagnostics, with next-generation sequencing techniques now allowing us to analyse hundreds of genes simultaneously. To ensure that patients benefit from these new techniques, adaptation of current diagnostic strategies is needed. On the basis of a systematic literature review of dystonia with onset in childhood or adolescence, we propose a novel diagnostic strategy with the aim of helping clinicians determine which patients may benefit by applying these new genetic techniques and which patients first require other investigations. We also provide an up-to-date list of candidate genes for a dystonia gene panel, based on a detailed literature search up to 20 October 2014. While new genetic techniques are certainly not a panacea, possible advantages of our proposed strategy include earlier diagnosis and avoidance of unnecessary investigations. It will therefore shorten the time of uncertainty for patients and their families awaiting a definite diagnosis.

Autosomal recessive cerebellar ataxia type 3 due to ANO10 mutations: delineation and genotype-phenotype correlation study.

IMPORTANCE: ANO10 mutations have been reported to cause a novel form of autosomal recessive cerebellar ataxia (ARCA). Our objective was to report 9 ataxic patients carrying 8 novel ANO10 mutations to improve the delineation of this form of ARCA and provide genotype-phenotype correlation. OBSERVATIONS: The ANO10 gene has been sequenced in 186 consecutive patients with ARCA. The detailed phenotype of patients with ANO10 mutations was investigated and compared with the 12 previously reported cases. The mean age at onset was 33 years (range, 17-43 years), and the disease progression was slow. Corticospinal tract signs were frequent, including extensor plantar reflexes and/or diffuse tendon reflexes and/or spasticity. No patient in our series had peripheral neuropathy. Magnetic resonance imaging of the brains of our patients revealed marked cerebellar atrophy. The most frequent mutation, a mononucleotide expansion from a polyA repeat tract (c.132dupA) that causes protein truncation, was never observed in homozygosity. Only 2 truncating mutations were reported in homozygosity, one of which (c.1150-1151del) was associated with juvenile or adolescent onset and mental retardation, whereas we show that the presence of at least 1 missense or in-frame mutation is associated with adult onset and slow progression. CONCLUSIONS AND RELEVANCE: An ANO10 mutation is responsible for ARCA that is mainly characterized by cerebellar atrophy and lack of peripheral neuropathy. We therefore suggest naming this entity autosomal recessive cerebellar ataxia type 3 (ARCA3).

Central 22q11.2 deletions.

22q11.2 deletion syndrome is one of the most common microdeletion syndromes. Most patients have a deletion resulting from a recombination of low copy repeat blocks LCR22-A and LCR22-D. Loss of the TBX1 gene is considered the most important cause of the phenotype. A limited number of patients with smaller, overlapping deletions distal to the TBX1 locus have been described in the literature. In these patients, the CRKL gene is deleted. Haploinsufficiency of this gene has also been implicated in the pathogenesis of 22q11.2 deletion syndrome. To distinguish these deletions (comprising the LCR22-B to LCR22-D region) from the more distal 22q11.2 deletions (located beyond LCR22-D), we propose the term "central 22q11.2 deletions". In the present study we report on 27 new patients with such a deletion. Together with information on previously published cases, we review the clinical findings of 52 patients. The prevalence of congenital heart anomalies and the frequency of de novo deletions in patients with a central deletion are substantially lower than in patients with a common or distal 22q11.2 deletion. Renal and urinary tract malformations, developmental delays, cognitive impairments and behavioral problems seem to be equally frequent as in patients with a common deletion. None of the patients had a cleft palate. Patients with a deletion that also encompassed the MAPK1 gene, located just distal to LCR22-D, have a different and more severe phenotype, characterized by a higher prevalence of congenital heart anomalies, growth restriction and microcephaly. Our results further elucidate genotype-phenotype correlations in 22q11.2 deletion syndrome spectrum.

Ramsay Hunt syndrome: clinical characterization of progressive myoclonus ataxia caused by GOSR2 mutation.

BACKGROUND: Ramsay Hunt syndrome (progressive myoclonus ataxia) is a descriptive diagnosis characterized by myoclonus, ataxia, and infrequent seizures. Often the etiology cannot be determined. Recently, a mutation in the GOSR2 gene (c.430G>T, p.Gly144Trp) was reported in 6 patients with childhood-onset progressive ataxia and myoclonus. METHODS: We evaluated 5 patients with cortical myoclonus, ataxia, and areflexia. RESULTS: All 5 patients had the same homozygous mutation in GOSR2. Here we present their clinical and neurophysiological data. Our patients (aged 7-26 years) all originated from the northern Netherlands and showed a remarkably homogeneous phenotype. Myoclonus and ataxia were relentlessly progressive over the years. Electromyography revealed signs of sensory neuronopathy or anterior horn cell involvement, or both, in all patients with absent reflexes. CONCLUSIONS: Based on the presented phenotype, we would advise movement disorder specialists to consider mutation analysis of GOSR2 in patients with Ramsay Hunt syndrome, especially when they also have areflexia.

Clinical and mutational characteristics of spinal muscular atrophy with respiratory distress type 1 in The Netherlands.

Spinal muscular atrophy with respiratory distress type 1 is an autosomal recessive disorder with early respiratory difficulties, distal muscle weakness, and contractures leading to foot deformities as the most striking clinical symptoms. Mutations of the gene encoding the immunoglobulin heavy chain µ-binding protein 2, mapped on chromosome 11q13, are the cause of the disease. We present the clinical and mutational characteristics of ten patients in the Netherlands who showed considerable clinical variability; they carried six novel mutations, including a deletion of exon 2. However, there were no clear phenotype-genotype correlations.