Pathogenic variants in TUBB4A are not found in primary dystonia

Prenatal MAM treatment altered fear conditioning following social isolation: Relevance to schizophrenia

Adolescent social isolation (SI) might change the trajectory of brain development. In the present study, we investigated the effect of short-term adolescent SI on fear memory, anxiety and protein levels in the adult medial prefrontal cortex of rats prenatally treated with methylazoxymethanol, MAM-E17 model of schizophrenia. The animals were maintained in standard housing (SH) or social isolation (P30-P40, SI) conditions. Behavioural tests (trace or delay fear conditioning, light/dark box) were performed in late adolescence and early adulthood. The results showed that MAM treatment did not alter fear memory, which was investigated with the use of either trace or delay fear conditioning, at any age, and SI decreased the fear response in adult control animals only under trace conditioning. Neither MAM nor SI influenced anxiety-related behaviour measured in the light/dark box. A proteomics study showed that both MAM and SI changed the protein levels related to synapse maturation and cytoskeletal organization, energy transfer and metabolic processes. Prenatal or adolescent environmental factors are able to change the expression of proteins that are correlated with behavioural impairments. Moreover, SI reversed some alterations in proteins induced by MAM. Thus, normally developing brains showed different responses to adolescent SI than those with altering courses of MAM administration.

TUBB4A mutations result in specific neuronal and oligodendrocytic defects that closely match clinically distinct phenotypes

Hypomyelinating leukodystrophies are heritable disorders defined by lack of development of brain myelin, but the cellular mechanisms of hypomyelination are often poorly understood. Mutations in TUBB4A, encoding the tubulin isoform tubulin beta class IVA (Tubb4a), result in the symptom complex of hypomyelination with atrophy of basal ganglia and cerebellum (H-ABC). Additionally, TUBB4A mutations are known to result in a broad phenotypic spectrum, ranging from primary dystonia (DYT4), isolated hypomyelination with spastic quadriplegia, and an infantile onset encephalopathy, suggesting multiple cell types may be involved. We present a study of the cellular effects of TUBB4A mutations responsible for H-ABC (p.Asp249Asn), DYT4 (p.Arg2Gly), a severe combined phenotype with hypomyelination and encephalopathy (p.Asn414Lys), as well as milder phenotypes causing isolated hypomyelination (p.Val255Ile and p.Arg282Pro). We used a combination of histopathological, biochemical and cellular approaches to determine how these different mutations may have variable cellular effects in neurons and/or oligodendrocytes. Our results demonstrate that specific mutations lead to either purely neuronal, combined neuronal and oligodendrocytic or purely oligodendrocytic defects that closely match their respective clinical phenotypes. Thus, the DYT4 mutation that leads to phenotypes attributable to neuronal dysfunction results in altered neuronal morphology, but with unchanged tubulin quantity and polymerization, with normal oligodendrocyte morphology and myelin gene expression. Conversely, mutations associated with isolated hypomyelination (p.Val255Ile and p.Arg282Pro) and the severe combined phenotype (p.Asn414Lys) resulted in normal neuronal morphology but were associated with altered oligodendrocyte morphology, myelin gene expression, and microtubule dysfunction. The H-ABC mutation (p.Asp249Asn) that exhibits a combined neuronal and myelin phenotype had overlapping cellular defects involving both neuronal and oligodendrocyte cell types in vitro. Only mutations causing hypomyelination phenotypes showed altered microtubule dynamics and acted through a dominant toxic gain of function mechanism. The DYT4 mutation had no impact on microtubule dynamics suggesting a distinct mechanism of action. In summary, the different clinical phenotypes associated with TUBB4A reflect the selective and specific cellular effects of the causative mutations. Cellular specificity of disease pathogenesis is relevant to developing targeted treatments for this disabling condition.

Phenomenology, genetics, and CNS network abnormalities in laryngeal dystonia: A 30-year experience

OBJECTIVE

Laryngeal dystonia (LD) is a functionally specific disorder of the afferent-efferent motor coordination system producing action-induced muscle contraction with a varied phenomenology. This report of long-term studies aims to review and better define the phenomenology and central nervous system abnormalities of this disorder and improve diagnosis and treatment.

METHODS

Our studies categorized over 1,400 patients diagnosed with LD over the past 33 years, including demographic and medical history records and their phenomenological presentations. Patients were grouped on clinical phenotype (adductor or abductor) and genotype (sporadic and familial) and with DNA analysis and functional magnetic resonance imaging (fMRI) to investigate brain organization differences and characterize neural markers for genotype/phenotype categorization. A number of patients with alcohol-sensitive dystonia were also studied.

RESULTS

A spectrum of LD phenomena evolved: adductor, abductor, mixed, singer's, dystonic tremor, and adductor respiratory dystonia. Patients were genetically screened for DYT (dystonia) 1, DYT4, DYT6, and DYT25 (GNAL)-and several were positive. The functional MRI studies showed distinct alterations within the sensorimotor network, and the LD patients with a family history had distinct cortical and cerebellar abnormalities. A linear discriminant analysis of fMRI findings showed a 71% accuracy in characterizing LD from normal and in characterizing adductor from abductor forms.

CONCLUSION

Continuous studies of LD patients over 30 years has led to an improved understanding of the phenomenological characteristics of this neurological disorder. Genetic and fMRI studies have better characterized the disorder and raise the possibility of making objective rather than subjective diagnoses, potentially leading to new therapeutic approaches. Laryngoscope, 128:S1-S9, 2018.

Rethinking status dystonicus

Status dystonicus is a movement disorder emergency that has been a source of controversy in terms of terminology, phenomenology, and management since it was first described in 1982. Here we argue that the current use of the term status dystonicus falls well short of the precision needed for either clinical or academic use. We performed a critical review on this topic, describing possible pathophysiological mechanisms and areas of uncertainties. This review also addresses the problems derived by the extreme clinical heterogeneity of this condition, as the lack of an objective criterion useful for the definition, or the fact that status dystonicus may present not only in the context of a known dystonic syndrome. We propose a new possible definition that includes not only dystonia but also other hyperkinetic movements in the wide range of movement disorders that can be seen during an episode. The new definition keeps the term status dystonicus and highlights the fact that this is a medical emergency based on the impairment of bulbar and/or respiratory function requiring hospital admission as the principal feature. Furthermore, the new definition should not consider as necessary unspecific features as patient's condition at baseline, the distribution of dystonia, occurrence of systemic symptoms such as fever or laboratory findings. We hope that this proposal will stimulate the debate on this subject among our peers, further developing a clinical and pathophysiological understanding of status dystonicus. © 2017 International Parkinson and Movement Disorder Society.

Screening study of TUBB4A in isolated dystonia

Mutations in TUBB4A have been identified to cause a wide phenotypic spectrum ranging from hereditary generalized dystonia with whispering dysphonia (DYT4) to the leukodystrophy hypomyelination syndrome with atrophy of the basal ganglia and cerebellum (H-ABC). To test for the contribution of TUBB4A mutations in different ethnicities (Spanish, Italian, Korean, Japanese), we screened 492 isolated dystonia cases for mutations in this gene and for the first time determined TUBB4A copy number variations in 336 dystonia patients. A potentially pathogenic rare 3bp-in-frame deletion was found in a patient with cervical dystonia but no copy number variations were detected in this study, suggesting that TUBB4A mutations exceedingly rarely contribute to the etiology of isolated dystonia.

Dystonia-Causing Mutations as a Contribution to the Etiology of Spasmodic Dysphonia

OBJECTIVE

Spasmodic dysphonia is a focal dystonia of the larynx with heterogeneous manifestations and association with familial risk factors. There are scarce data to allow precise understanding of etiology and pathophysiology. Screening for dystonia-causing genetic mutations has the potential to allow accurate diagnosis, inform about genotype-phenotype correlations, and allow a better understanding of mechanisms of disease.

STUDY DESIGN

Cross-sectional study.

SETTING

Tertiary academic medical center.

SUBJECTS AND METHODS

We enrolled patients presenting with spasmodic dysphonia to the voice clinic of our academic medical center. Data included demographics, clinical features, family history, and treatments administered. The following genes with disease-causing mutations previously associated with spasmodic dysphonia were screened: TOR1A (DYT1), TUBB4 (DYT4), and THAP1 (DYT6).

RESULTS

Eighty-six patients were recruited, comprising 77% females and 23% males. A definite family history of neurologic disorder was present in 15% (13 of 86). Average age (± standard deviation) of symptom onset was 42.1 ± 15.7 years. Most (99%; 85 of 86) were treated with botulinum toxin, and 12% (11 of 86) received oral medications. Genetic screening was negative in all patients for the GAG deletion in TOR1A (DYT1) and in the 5 exons currently associated with disease-causing mutations in TUBB4 (DYT4). Two patients tested positive for novel/rare variants in THAP1 (DYT6).

CONCLUSION

Genetic screening targeted at currently known disease-causing mutations in TOR1A, THAP1, and TUBB4 appears to have low diagnostic yield in sporadic spasmodic dysphonia. In our cohort, only 2 patients tested positive for novel/rare variants in THAP1. Clinicians should make use of genetic testing judiciously and in cost-effective ways.

Large-scale TUBB4A mutational screening in isolated dystonia and controls

INTRODUCTION

Mutations in TUBB4A have recently been implicated in two seemingly different disease entities, namely DYT4-isolated dystonia and hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC), a disorder characterized by considerable clinical variability. While several follow-up studies confirmed the importance of TUBB4A mutations in the development of H-ABC, their contribution to isolated dystonia remains uncertain.

METHODS

We screened the TUBB4A coding regions in a large population of 709 isolated dystonia patients of German/Austrian ancestry as well as in 376 ancestry-matched control subjects by means of Sanger sequencing and high-resolution melting. In addition, we assessed the overall frequency of rare non-synonymous TUBB4A genetic variation in the huge exome dataset released by the Exome Aggregation Consortium (ExAC).

RESULTS

We were unable to identify any possibly pathogenic sequence alteration in either patients or controls. According to ExAC, the overall prevalence of rare missense and loss-of-function alleles in the TUBB4A gene can be estimated at ∼1:706.

CONCLUSIONS

In accordance with previous work, our data indicate that TUBB4A coding mutations do not play a critical role in the broad population of isolated dystonia patients. Rather, isolated dystonia as seen in DYT4 might be an exceptional feature occurring in the heterogeneous phenotypic spectrum due to TUBB4A mutations.

The genetics of the dystonias--a review based on the new classification of the dystonias

The definition and classification of the dystonias was recently revisited. In the new 2013 classification, the dystonias are subdivided in terms of their etiology according to whether they are the result of pathological changes or structural damage, have acquired causes or are inherited. As hereditary dystonias are clinically and genetically heterogeneous, we sought to classify them according to the new recently defined criteria. We observed that although the new classification is still the subject of much debate and controversy, it is easy to use in a logical and objective manner with the inherited dystonias. With the discovery of new genes, however, it remains to be seen whether the new classification will continue to be effective.

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.