The expanding clinical and genetic spectrum of ANO3 dystonia

Broadening the clinical spectrum: molecular mechanisms and new phenotypes of ANO3-dystonia

Anoctamin 3 (ANO3) belongs to a family of transmembrane proteins that form phospholipid scramblases and ion channels. A large number of ANO3 variants were identified as the cause of craniocervical dystonia, but the underlying pathogenic mechanisms remain obscure. It was suggested that ANO3 variants may dysregulate intracellular Ca2+ signalling, as variants in other Ca2+ regulating proteins like hippocalcin were also identified as a cause of dystonia. In this study, we conducted a comprehensive evaluation of the clinical, radiological and molecular characteristics of four individuals from four families who carried heterozygous variants in ANO3. The median age at follow-up was 6.6 years (ranging from 3.8 to 8.7 years). Three individuals presented with hypotonia and motor developmental delay. Two patients exhibited generalized progressive dystonia, while one patient presented with paroxysmal dystonia. Additionally, another patient exhibited early dyskinetic encephalopathy. One patient underwent bipallidal deep brain stimulation (DBS) and showed a mild but noteworthy response, while another patient is currently being considered for DBS treatment. Neuroimaging analysis of brain MRI studies did not reveal any specific abnormalities. The molecular spectrum included two novel ANO3 variants (V561L and S116L) and two previously reported ANO3 variants (A599D and S651N). As anoctamins are suggested to affect intracellular Ca2+ signals, we compared Ca2+ signalling and activation of ion channels in cells expressing wild-type ANO3 and cells expressing anoctamin variants. Novel V561L and S116L variants were compared with previously reported A599D and S651N variants and with wild-type ANO3 expressed in fibroblasts isolated from patients or when overexpressed in HEK293 cells. We identified ANO3 as a Ca2+-activated phospholipid scramblase that also conducts ions. Impaired Ca2+ signalling and compromised activation of Ca2+-dependent K+ channels were detected in cells expressing ANO3 variants. In the brain striatal cells of affected patients, impaired activation of KCa3.1 channels due to compromised Ca2+ signals may lead to depolarized membrane voltage and neuronal hyperexcitability and may also lead to reduced cellular viability, as shown in the present study. In conclusion, our study reveals the association between ANO3 variants and paroxysmal dystonia, representing the first reported link between these variants and this specific dystonic phenotype. We demonstrate that ANO3 functions as a Ca2+-activated phospholipid scramblase and ion channel; cells expressing ANO3 variants exhibit impaired Ca2+ signalling and compromised activation of Ca2+-dependent K+ channels. These findings provide a mechanism for the observed clinical manifestations and highlight the importance of ANO3 for neuronal excitability and cellular viability.

The Clinical Spectrum of ANO3-Report of a New Family and Literature Review

BACKGROUND

Mutations in ANO3 are a rare cause of autosomal dominant isolated or combined dystonia, mainly presenting in adulthood.

CASES

We extensively characterize a new, large ANO3 family with six affected carriers. The proband is a young girl who had suffered from tremor and painful dystonic movements in her right arm since the age of 11 years. She later developed a diffuse dystonic tremor and mild extrapyramidal signs (ie, rigidity and hypodiadochokinesis) in her right arm. She also suffered from psychomotor delay and learning difficulties. Repeated structural and functional neuroimaging were unremarkable. A dystonic tremor was also present in her two sisters. Her paternal aunt, father, and a third older sister presented episodic postural tremor in the arms. The father and one sister also presented learning difficulties. The heterozygous p.G6V variant in ANO3 was identified in all affected subjects.

LITERATURE REVIEW

Stratification by age at onset divided ANO3 cases into two major groups, where younger patients displayed a more severe phenotype, probably due to variants near the scrambling domain.

CONCLUSIONS

We describe the phenotype of a new ANO3 family and highlight the need for functional studies to explore the impact of ANO3 variants on its phospholipid scrambling activity.

Dystonia and tremor: Do they have a shared biology?

Dystonia and tremor are the two most commonly encountered hyperkinetic movement disorders encountered in clinical practice. While there has been substantial progress in the research on these two disorders, there also exists a lot of gray areas. Entities such as dystonic tremor and tremor associated with dystonia occupy a major portion of the "gray zone". In addition, there is a marked clinical heterogeneity and overlap of several clinical and epidemiological features among dystonia and tremor. These facts raise the possibility that dystonia and tremor could be having shared biology. In this chapter, we revisit critical aspects of this possibility that may have important clinical and research implications in the future. We comprehensively review the points in favor and against the theory that dystonia and tremor have shared biology from clinical, epidemiological, genetic and neuroimaging studies.

Adult-onset focal dystonias: To lump or split

The adult-onset focal dystonias are a group of clinically heterogeneous disorders that affect different regions of the body. Although they affect different regions with different clinical manifestations, there is evidence that etiopathogenesis is shared at the anatomical, physiological, and genetic levels. However, there is also evidence that etiopathogenesis varies. This chapter summarizes the evidence for lumping or splitting these apparently different clinical phenotypes. It also includes some potential explanations to explain the similarities and differences.

A novel variant in the transmembrane 4 domain of ANO3 identified in a two-year-old girl with developmental delay and tremor

ANO3 encodes Anoctamin-3, also known as TMEM16C, a calcium-activated chloride channel. Heterozygous variants of ANO3 can cause dystonia 24, an adult-onset focal dystonia. Some pediatric cases have been reported, but most patients were intellectually normal with some exceptions. Here, we report a two-year-old girl who showed mild to moderate developmental delay, tremor, and ataxic gait, but no obvious dystonia. Trio exome sequencing identified a heterozygous de novo missense variant NM_031418.4:c.1809T>G, p.(Asn603Lys) in the ANO3 gene. Three cases with ANO3 variants and intellectual disability have been reported, including the present case. These variants were predicted to face in the same direction on the same alpha-helix (the transmembrane 4 domain), suggesting an association between these variants and childhood-onset movement disorder with intellectual disability. In pediatric cases with developmental delay and movement disorders such as tremor and ataxia, specific variants in the transmembrane 4 domain of ANO3 may be a cause, even in the absence of dystonia.

Dystonia Diagnosis: Clinical Neurophysiology and Genetics

Dystonia diagnosis is based on clinical examination performed by a neurologist with expertise in movement disorders. Clues that indicate the diagnosis of a movement disorder such as dystonia are dystonic movements, dystonic postures, and three additional physical signs (mirror dystonia, overflow dystonia, and geste antagonists/sensory tricks). Despite advances in research, there is no diagnostic test with a high level of accuracy for the dystonia diagnosis. Clinical neurophysiology and genetics might support the clinician in the diagnostic process. Neurophysiology played a role in untangling dystonia pathophysiology, demonstrating characteristic reduction in inhibition of central motor circuits and alterations in the somatosensory system. The neurophysiologic measure with the greatest evidence in identifying patients affected by dystonia is the somatosensory temporal discrimination threshold (STDT). Other parameters need further confirmations and more solid evidence to be considered as support for the dystonia diagnosis. Genetic testing should be guided by characteristics such as age at onset, body distribution, associated features, and coexistence of other movement disorders (parkinsonism, myoclonus, and other hyperkinesia). The aim of the present review is to summarize the state of the art regarding dystonia diagnosis focusing on the role of neurophysiology and genetic testing.

Coenzyme Q10 enhances remyelination and regulate inflammation effects of cuprizone in corpus callosum of chronic model of multiple sclerosis

Multiple Sclerosis (MS) is a chronic, progressive demyelinating disease of the central nervous system that causes the most disability in young people, besides trauma. Coenzyme Q10 (CoQ10)-also known as ubiquinone-is an endogenous lipid-soluble antioxidant in the mitochondrial oxidative respiratory chain which can reduce oxidative stress and inflammation, the processes associated with demyelination in MS. Cuprizone (CPZ) intoxication is a well-established model of inducing MS, best for studying demyelination-remyelination. In this study, we examined for the first time the role of CoQ10 in preventing demyelination and induction of remyelination in the chronic CPZ model of MS. 40 male mice were divided into four groups. 3 group chewed CPZ-containing food for 12 weeks to induce MS. After 4 weeks, one group were treated with CoQ10 (150 mg/kg/day) by daily gavage until the end of the experiment, while CPZ poisoning continued. At the end of 12 weeks, tail suspension test (TST) and open field test (OFT) was taken and animals were sacrificed to assess myelin basic protein (MBP), oligodendrocyte transcription factor-1 (Olig1), tumor necrosis factor-α (TNF-α) and interleukin 6 (IL-6) by real-time polymerase chain reaction (real-time PCR) and total antioxidant capacity (TAC) and superoxide dismutase (SOD) by Elisa test. Luxol fast blue (LFB) staining was used to evaluate histological changes. CoQ10 administration promoted remyelination in histological findings. MBP and Olig-1 expression were increased significantly in CoQ10 treated group compare to the CPZ-intoxicated group. CoQ10 treatment alleviated stress oxidative status induced by CPZ and dramatically suppress inflammatory biomarkers. CPZ ingestion made no significant difference between normal control group and the CPZ-intoxicated group in TST and OFT. CoQ10 can enhance remyelination in the CPZ model and potentially might have same effects in MS patients.