A Yorkshire family with adult-onset cranio-cervical primary torsion dystonia

Isolated and combined genetic tremor syndromes: a critical appraisal based on the 2018 MDS criteria

The 2018 consensus statement on the classification of tremors proposes a two-axis categorization scheme based on clinical features and etiology. It also defines "isolated" and "combined" tremor syndromes depending on whether tremor is the sole clinical manifestation or is associated with other neurological or systemic signs. This syndromic approach provides a guide to investigate the underlying etiology of tremors, either genetic or acquired. Several genetic defects have been proven to cause tremor disorders, including autosomal dominant and recessive, X-linked, and mitochondrial diseases, as well as chromosomal abnormalities. Furthermore, some tremor syndromes are recognized in individuals with a positive family history, but their genetic confirmation is pending. Although most genetic tremor disorders show a combined clinical picture, there are some distinctive conditions in which tremor may precede the appearance of other neurological signs by years or remain the prominent manifestation throughout the disease course, previously leading to misdiagnosis as essential tremor (ET). Advances in the knowledge of genetically determined tremors may have been hampered by the inclusion of heterogeneous entities in previous studies on ET. The recent classification of tremors therefore aims to provide more consistent clinical data for deconstructing the genetic basis of tremor syndromes in the next-generation and long-read sequencing era. This review outlines the wide spectrum of tremor disorders with defined or presumed genetic etiology, both isolated and combined, unraveling diagnostic clues of these conditions and focusing mainly on ET-like phenotypes. Furthermore, we suggest a phenotype-to-genotype algorithm to support clinicians in identifying tremor syndromes and guiding genetic investigations.

Youngest presenting patient with dystonia 24 and review of the literature

Dystonia 24 was first reported in 2000 as an autosomal dominant cause of dystonia caused by variants in the ANO3 gene. Although many adults have been described with dystonia 24, since 2014, an increasing number of children have also been reported. Dystonia 24 should also be considered in the differential of a child with unexplained dystonia.

A novel ANO3 variant identified in a 53-year-old woman presenting with hyperkinetic dysarthria, blepharospasm, hyperkinesias, and complex motor tics

Background

Cervical dystonias have a variable presentation and underlying etiology, but collectively represent the most common form of focal dystonia. There are a number of known genetic forms of dystonia (DYT1-27); however the heterogeneity of disease presentation does not always make it easy to categorize the disease by phenotype-genotype comparison.

Case presentation

In this report, we describe a 53-year-old female who presented initially with hand tremor following a total hip arthroplasty. The patient developed a mixed hyperkinetic disorder consisting of chorea, dystonia affecting the upper extremities, dysarthria, and blepharospasm. Whole exome sequencing of the patient revealed a novel heterozygous missense variant (Chr11(GRCh38): g.26525644C > G; NM_031418.2(ANO3): c.702C > G; NP_113606.2. p.C234W) in exon 7 in the ANO3 gene.

Conclusions

ANO3 encodes anoctamin-3, a Ca⁺²-dependent phospholipid scramblase expressed in striatal-neurons, that has been implicated in autosomal dominant craniocervical dystonia (Dystonia-24, DYT24, MIM# 615034). To date, only a handful of cases of DYT-24 have been described in the literature. The complex clinical presentation of the patient described includes hyperkinesias, complex motor movements, and vocal tics, which have not been reported in other patients with DYT24. This report highlights the utility of using clinical whole exome sequencing in patients with complex neurological phenotypes that would not normally fit a classical presentation of a defined genetic disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-016-0354-7) contains supplementary material, which is available to authorized users.

Exposure of phosphatidylserine on the cell surface

Phosphatidylserine (PtdSer) is a phospholipid that is abundant in eukaryotic plasma membranes. An ATP-dependent enzyme called flippase normally keeps PtdSer inside the cell, but PtdSer is exposed by the action of scramblase on the cell's surface in biological processes such as apoptosis and platelet activation. Once exposed to the cell surface, PtdSer acts as an 'eat me' signal on dead cells, and creates a scaffold for blood-clotting factors on activated platelets. The molecular identities of the flippase and scramblase that work at plasma membranes have long eluded researchers. Indeed, their identity as well as the mechanism of the PtdSer exposure to the cell surface has only recently been revealed. Here, we describe how PtdSer is exposed in apoptotic cells and in activated platelets, and discuss PtdSer exposure in other biological processes.

Recent advances in the genetics of dystonia

Dystonia, a common and genetically heterogeneous neurological disorder, was recently defined as "a movement disorder characterized by sustained or intermittent muscle contractions causing abnormal, often repetitive, movements, postures, or both." Via the application of whole-exome sequencing, the genetic landscape of dystonia and closely related movement disorders is becoming exposed. In particular, several "novel" genetic causes have been causally associated with dystonia or dystonia-related disorders over the past 2 years. These genes include PRRT2 (DYT10), CIZ1 (DYT23), ANO3 (DYT24), GNAL (DYT25), and TUBB4A (DYT4). Despite these advances, major gaps remain in identifying the genetic origins for most cases of adult-onset isolated dystonia. Furthermore, model systems are needed to study the biology of PRRT2, CIZ1, ANO3, Gαolf, and TUBB4A in the context of dystonia. This review focuses on these recent additions to the family of dystonia genes, genotype-phenotype correlations, and possible cellular contributions of the encoded proteins to the development of dystonia.

The phenotypic spectrum of DYT24 due to ANO3 mutations

Genes causing primary dystonia are rare. Recently, pathogenic mutations in the anoctamin 3 gene (ANO3) have been identified to cause autosomal dominant craniocervical dystonia and have been assigned to the dystonia locus dystonia-24 (DYT24). Here, we expand on the phenotypic spectrum of DYT24 and provide demonstrative videos. Moreover, tremor recordings were performed, and back-averaged electroencephalography, sensory evoked potentials, and C-reflex studies were carried out in two individuals who carried two different mutations in ANO3. Ten patients from three families are described. The age at onset ranged from early childhood to the forties. Cervical dystonia was the most common site of onset followed by laryngeal dystonia. The characteristic feature in all affected individuals was the presence of tremor, which contrasts DYT24 from the typical DYT6 phenotype. Tremor was the sole initial manifestation in some individuals with ANO3 mutations, leading to misdiagnosis as essential tremor. Electrophysiology in two patients with two different mutations showed co-contraction of antagonist muscles, confirming dystonia, and a 6-Hz arm tremor at rest, which increased in amplitude during action. In one of the studied patients, clinically superimposed myoclonus was observed. The duration of the myoclonus was in the range of 250 msec at about 3 Hz, which is more consistent with subcortical myoclonus. In summary, ANO3 causes a varied phenotype of young-onset or adult-onset craniocervical dystonia with tremor and/or myoclonic jerks. Patients with familial cervical dystonia who also have myoclonus-dystonia as well as patients with prominent tremor and mild dystonia should be tested for ANO3 mutations. © 2014 The Authors. Movement Disorders published by International Parkinson and Movement Disorder Society

The focal dystonias: current views and challenges for future research

The most common forms of dystonia are those that develop in adults and affect a relatively isolated region of the body. Although these adult-onset focal dystonias are most prevalent, knowledge of their etiologies and pathogenesis has lagged behind some of the rarer generalized dystonias, in which the identification of genetic defects has facilitated both basic and clinical research. This summary provides a brief review of the clinical manifestations of the adult-onset focal dystonias, focusing attention on less well understood clinical manifestations that need further study. It also provides a simple conceptual model for the similarities and differences among the different adult-onset focal dystonias as a rationale for lumping them together as a class of disorders while at the same time splitting them into subtypes. The concluding section outlines some of the most important research questions for the future. Answers to these questions are critical for advancing our understanding of this group of disorders and for developing novel therapeutics.

The environmental epidemiology of primary dystonia

BACKGROUND

Dystonia is a movement disorder characterized by involuntary muscle contractions that cause twisting movements and abnormal postures. Primary dystonia is the most common form and is thought to be a multifactorial condition in which one or more genes combine with environmental factors to reach disease.

METHODS

We reviewed controlled studies on possible environmental risk factors for primary early- and late-onset dystonia.

RESULTS

Environmental factors associated with primary early-onset dystonia are poorly understood. Early childhood illnesses have been reported to be more frequent in patients with DYT1 dystonia than in subjects carrying the DYT1 mutation that did not manifest dystonia, thus raising the possibility that such exposures precipitate dystonia among DYT1 carriers. Conversely, several environmental factors have been associated with primary adult-onset focal dystonias compared to control subjects. Namely, eye diseases, sore throat, idiopathic scoliosis, and repetitive upper limb motor action seem to be associated with blepharospasm (BSP), laryngeal dystonia (LD), cervical dystonia (CD), and upper limb dystonia, respectively. In addition, an inverse association between coffee drinking and BSP has been observed in both case-unrelated control and family-based case-control studies. Additional evidence supporting a causal link with different forms of primary late-onset dystonia is only available for diseases of the anterior segment of the eye, writing activity, and coffee intake.

CONCLUSION

There is reasonable epidemiological evidence that some environmental factors are risk-modifying factors for specific forms of primary adult-onset focal dystonia.

Tremulous cervical dystonia is likely to be familial: clinical characteristics of a large cohort

BACKGROUND

Primary cervical dystonia is the most common form of adult-onset focal dystonia. Although most frequently sporadic, 15-20% of patients report a positive family history, suggesting a possible genetic cause. Head tremor is often present in patients with cervical dystonia and may be a prominent symptom.

OBJECTIVE

To describe the clinical characteristics of patients with tremulous cervical dystonia.

METHODS

Patients with primary cervical dystonia attending our botulinum toxin clinic were assessed with an interview and neurological examination and their notes reviewed. Patients were classified as having either tremulous or non-tremulous cervical dystonia, according to the presence or absence of head tremor on examination. Clinical and demographic data were compared between groups.

RESULTS

From 273 patients included (190 females, 83 males), 125 (46%) were classified as tremulous and 148 (54%) as non-tremulous. Tremulous patients were more likely to have a segmental distribution (61% vs. 25%), often involving the arms (48%), and had more frequently associated arm tremor (55% vs. 10%). A positive family history of dystonia and/or tremor was more frequent in tremulous patients (50% vs. 18%).

CONCLUSIONS

Patients with cervical dystonia with associated head tremor are more likely to have a segmental distribution (with frequent arm involvement), associated arm tremor and a positive family history, suggesting a genetic etiology in this subgroup of patients.

Mutations in ANO3 cause dominant craniocervical dystonia: ion channel implicated in pathogenesis

In this study, we combined linkage analysis with whole-exome sequencing of two individuals to identify candidate causal variants in a moderately-sized UK kindred exhibiting autosomal-dominant inheritance of craniocervical dystonia. Subsequent screening of these candidate causal variants in a large number of familial and sporadic cases of cervical dystonia led to the identification of a total of six putatively pathogenic mutations in ANO3, a gene encoding a predicted Ca(2+)-gated chloride channel that we show to be highly expressed in the striatum. Functional studies using Ca(2+) imaging in case and control fibroblasts demonstrated clear abnormalities in endoplasmic-reticulum-dependent Ca(2+) signaling. We conclude that mutations in ANO3 are a cause of autosomal-dominant craniocervical dystonia. The locus DYT23 has been reserved as a synonym for this gene. The implication of an ion channel in the pathogenesis of dystonia provides insights into an alternative mechanism that opens fresh avenues for further research.

Mutations in CIZ1 cause adult onset primary cervical dystonia

OBJECTIVE

Primary dystonia is usually of adult onset, can be familial, and frequently involves the cervical musculature. Our goal was to identify the causal mutation in a family with adult onset, primary cervical dystonia.

METHODS

Linkage and haplotype analyses were combined with solution-based whole-exome capture and massively parallel sequencing in a large Caucasian pedigree with adult onset, primary cervical dystonia to identify a cosegregating mutation. High-throughput screening and Sanger sequencing were completed in 308 Caucasians with familial or sporadic adult onset cervical dystonia and matching controls for sequence variants in this mutant gene.

RESULTS

Exome sequencing led to the identification of an exonic splicing enhancer mutation in exon 7 of CIZ1 (c.790A>G, p.S264G), which encodes CIZ1, Cip1-interacting zinc finger protein 1. CIZ1 is a p21(Cip1/Waf1) -interacting zinc finger protein expressed in brain and involved in DNA synthesis and cell-cycle control. Using a minigene assay, we showed that c.790A>G altered CIZ1 splicing patterns. The p.S264G mutation also altered the nuclear localization of CIZ1. Screening in subjects with adult-onset cervical dystonia identified 2 additional CIZ1 missense mutations (p.P47S and p.R672M).

INTERPRETATION

Mutations in CIZ1 may cause adult onset, primary cervical dystonia, possibly by precipitating neurodevelopmental abnormalities that manifest in adults and/or G1/S cell-cycle dysregulation in the mature central nervous system.

Milestones in dystonia

The last 25 years have seen remarkable advances in our understanding of the genetic etiologies of dystonia, new approaches into dissecting underlying pathophysiology, and independent progress in identifying effective treatments. In this review we highlight some of these advances, especially the genetic findings that have taken us from phenomenological to molecular-based diagnoses. Twenty DYT loci have been designated and 10 genes identified, all based on linkage analyses in families. Hand in hand with these genetic findings, neurophysiological and imaging techniques have been employed that have helped illuminate the similarities and differences among the various etiological dystonia subtypes. This knowledge is just beginning to yield new approaches to treatment including those based on DYT1 animal models. Despite the lag in identifying genetically based therapies, effective treatments, including impressive benefits from deep brain stimulation and botulinum toxin chemodenervation, have marked the last 25 years. The challenge ahead includes continued advancement into understanding dystonia's many underlying causes and associated pathology and using this knowledge to advance treatment including preventing genetic disease expression.

Genetic and clinical features of primary torsion dystonia

Primary torsion dystonia (PTD) is defined as a syndrome in which dystonia is the only clinical sign (except for tremor), and there is no evidence of neuronal degeneration or an acquired cause by history or routine laboratory assessment. Seven different loci have been recognized for PTD but only two of the genes have been identified. In this review we will describe the phenotypes associated with these loci and discuss the responsible gene. This article is part of a Special Issue entitled "Advances in dystonia".

Genetics and treatment of dystonia

The torsion dystonias encompass a broad collection of etiologic subtypes, often divided into primary and secondary classes. Tremendous advances have been made in uncovering the genetic basis of dystonia, including discovery of a gene causing early onset primary torsion dystonia-a GAG deletion in exon 5 of the DYT1 gene that encodes torsinA. Although the exact function of torsinA remains elusive, evidence suggests aberrant localization and interaction of mutated protein; this may result in an abnormal response to stress or interference with cytoskeletal events and the development of neuronal brain pathways. Breakthroughs include the discovery of a genetic modifier that protects against clinical expression in DYT1 dystonia and the identification of the gene causing DYT6, THAP1. The authors review genetic etiologies and discuss phenotypes as well as counseling of patients regarding prognosis and progression of the disease. They also address pharmacologic and surgical treatment options for various forms of dystonia.

Non-DYT1 early-onset primary torsion dystonia: comparison with DYT1 phenotype and review of the literature

To investigate the clinical features of early-onset primary torsion dystonia (EO-PTD), 57 consecutive genetically characterized patients with onset before 21 years were studied. Sex, ethnic origin, family history of dystonia, age at onset, disease duration, site of dystonia onset and distribution at latest examination, dystonia progression, time to generalization, and motor disability were noted. The 14 patients (25%) with GAG deletion (904_906/907_909delGAG) in the DYT1 gene were compared with the remaining non-DYT1 patients. Cranial involvement was present in 49% of non-DYT1 cases, but only 14% of DYT1 cases; non-DYT1 patients were younger at time of generalization. DYT1 cases had features similar to sporadic non-DYT1 cases but differed markedly from familial non-DYT1 cases, the latter having later age at onset, less common limb onset, more frequent cervical involvement, and slower progression than DYT1 PTD. These findings indicate that non-DYT1 forms of EO-PTD differ clinically from those of DYT1 forms. Cranial involvement before 21 years of age is the strongest predictor of non-DYT1 status. Positive family history and cervical involvement are associated with less severe progression in non-DYT1 forms.

Unbalanced whole arm translocation resulting in loss of 18p in dystonia

Dystonia represents a genetically and clinically heterogeneous disorder, characterized by abnormal and sustained muscle contractions and rigid postures. At least 15 different loci (DYT1-DYT15) have been identified in dystonia. Adult-onset idiopathic focal dystonia affecting specific parts of the body, such as the eye (blepharospasm), neck (cervical dystonia), and hand (writer's cramp), is mostly associated with the DYT7 locus, which was originally mapped to chromosome 18p by genomewide linkage analysis in a large family showing autosomal dominant inheritance. We have identified a family in which the mother is affected with dystonia and the son shows signs of dystonia. Using fluorescent BAC probes spanning 18p, we were able to identify a deletion in these two individuals, spanning the entire short arm of 18p. This deletion is accompanied by a centric fusion involving chromosome 14. The 18p deleted region spans 15 megabases of DNA, with a number of interesting DYT7 candidate genes, including genes involved in G-protein-coupled signaling (GNAL), cell death (CIDEA), muscle development (MYOM1 and MRLM), mitochondrial activity (NDUFV2), and neuronal function (ADYCAP1, TGIF, DAP-1, and AFG3L2).

A family study on primary blepharospasm

BACKGROUND

Previous family studies provided evidence that blepharospasm (BSP) can aggregate in families but did not give accurate and reliable information on the characteristics and degree of familial clustering.

AIM

To evaluate the proportion of familial and non-familial BSP cases, the clinical expression of dystonia within families, the inheritance pattern, and the extent of penetrance.

METHODS

The study was based on the examination of the first degree relatives of 56 probands with primary BSP.

RESULTS

The 56 families produced a potential population of 436 first degree relatives of whom 296 were alive and 233 were examined. The proportion of index patients with at least one first degree relative affected by BSP, or adult onset dystonia other than BSP, was 27%. There was a remarkable degree of phenotypic variability of dystonia within families. Similar segregation ratios were calculated for probands' siblings and children. Under the assumption of autosomal dominant transmission of adult onset dystonia, penetrance was about 20%.

CONCLUSIONS

The findings of this family study are relevant for accurately counselling the families of patients with BSP and may help identify the most appropriate study design to explore genetic susceptibility in BSP.

A new screening tool for cervical dystonia

BACKGROUND

Family studies of dystonia may be limited in part by small family size and incomplete ascertainment of dystonia in geographically dispersed families. Further, prevalence estimates of dystonia are believed to be underestimates, as most studies are clinic-based and many individuals do not present to a physician or are misdiagnosed. As a low-cost highly sensitive screening tool is needed to improve case detection for genetic and epidemiologic studies, the authors developed the Beth Israel Dystonia Screen (BIDS), a computer-assisted telephone interview.

OBJECTIVE

To evaluate the validity and utility of a computer-assisted telephone interview in screening for cervical dystonia.

METHODS

The BIDS was administered and videotaped neurologic examinations performed on 193 individuals from 16 families with cervical and cranial dystonia. With use of a final rating of definite dystonia, as determined by video review of a systematic neurologic evaluation, as the gold standard, the predictive value of a subset of questions from the BIDS was assessed.

RESULTS

A positive response to at least two of five screening questions had a sensitivity for cervical dystonia of 100% and a specificity of 92%. With use of a positive response to three or more questions, definite dystonia was determined with 81% sensitivity and 97% specificity.

CONCLUSIONS

The Beth Israel Dystonia Screen (BIDS) identifies cervical dystonia with excellent sensitivity and specificity in a family-based sample. The authors recommend the BIDS for family studies, but cross-validation in a population sample is advisable before applying this method to epidemiologic studies.

Classification and genetics of dystonia

Dystonia is a syndrome characterised by sustained muscle contractions, producing twisting, repetitive, and patterned movements, or abnormal postures. The dystonic syndromes include a large group of diseases that have been classified into various aetiological categories, such as primary, dystonia-plus, heredodegenerative, and secondary. The diverse clinical features of these disorders are reflected in the traditional clinical classification based on age at onset, distribution of symptoms, and site of onset. However, with an increased awareness of the molecular and environmental causes, the classification schemes have changed to reflect different genetic forms of dystonia. To date, at least 13 dystonic syndromes have been distinguished on a genetic basis and their loci are referred to as DYT1 to DYT13. This review focuses on the molecular and phenotypic features of the hereditary dystonias, with emphasis on recent advances.

The genetics of primary dystonias and related disorders

Dystonias are a heterogeneous group of disorders which are known to have a strong inherited basis. This review details recent advances in our understanding of the genetic basis of dystonias, including the primary dystonias, the 'dystonia-plus' syndromes and heredodegenerative disorders. The review focuses particularly on clinical and genetic features and molecular mechanisms. Conditions discussed in detail include idiopathic torsion dystonia (DYT1), focal dystonias (DYT7) and mixed dystonias (DYT6 and DYT13), dopa-responsive dystonia, myoclonus dystonia, rapid-onset dystonia parkinsonism, Fahr disease, Aicardi-Goutieres syndrome, Hallervorden-Spatz syndrome, X-linked dystonia parkinsonism, deafness-dystonia syndrome, mitochondrial dystonias, neuroacanthocytosis and the paroxysmal dystonias/dyskinesias.

Novel Italian family supports clinical and genetic heterogeneity of primary adult-onset torsion dystonia

We report on an Italian kindred with adult-onset primary torsion dystonia (PTD). A detailed clinical examination of the six definitely affected family members revealed a mild, purely focal phenotype. The disease involved only one body part (eyes, neck, or arm). PTD in this family was not linked to the known disease loci (DYT1, DYT6, DYT7, and DYT13), and the 3-bp deletion in the DYT1 gene was also excluded. These findings support genetic heterogeneity of PTD and indicate that a novel unassigned gene is responsible for focal dystonia in this family.

Dystonia and its disorders

Dystonia is a movement disorder characterized by sustained muscle contractions, frequently causing twisting and repetitive movements or abnormal postures. The term dystonia does not signify a single disease, but instead describes a symptom and sign that may be part of many disorders with a variety of causes. Dystonia may be classified by age of onset, distribution of symptoms, or by etiology. An increasing number of genetic forms of dystonia have been recognized and the findings have advanced knowledge of underlying neural mechanisms of pathogenesis. Options for treatment of dystonia include pharmacological therapy, botulinum toxin injection, or neurosurgical procedures.