Introduction

Cervical dystonia (CD), also known as spasmodic torticollis, is a neurological movement disorder characterised by involuntary, sustained muscle contractions of the neck and shoulders, leading to abnormal postures, tremors, and often debilitating pain. As the most common form of focal dystonia, it significantly impairs quality of life, affecting daily activities, social interactions, and mental health. While the majority of cases are sporadic, emerging evidence underscores a substantial genetic contribution, particularly in familial forms where multiple relatives are affected.

 The etiology of cervical dystonia involves complex interactions between genetic predispositions and environmental factors. Recent advances in molecular genetics have identified several monogenic causes, including mutations in TOR1A (DYT1), THAP1 (DYT6), ANO3 (DYT24), and GNAL (DYT25), which collectively account for a significant proportion of familial cases. These discoveries have not only refined diagnostic precision but also illuminated pathophysiological mechanisms, such as dysfunction in synaptic transmission, neuronal signaling, and sensorimotor integration. Despite these insights, cervical dystonia remains underdiagnosed and often misattributed to orthopedic or psychiatric conditions. 

Diagnosis is primarily clinical, relying on recognising characteristic features and excluding secondary causes. Treatment strategies, though not curative, have evolved considerably. Botulinum toxin injections represent first-line therapy, providing symptomatic relief for most patients, while deep brain stimulation offers hope for those refractory to conventional management. This article explores the genetic foundations, clinical spectrum, and therapeutic advancements in cervical dystonia, emphasizing the translational impact of genetic research on diagnosis, counseling, and emerging targeted therapies.

What is cervical dystonia?

Cervical dystonia, otherwise known as spasmodic torticollis, is a rare neurological movement disorder characterised by involuntary muscle contractions in the neck, leading to abnormal head postures, tremors, and pain. In some cases, these abnormal contractions may be sustained or continuous, whilst in others, they may be spasmic or resemble tremors. Thus, the severity of CD can greatly differ between patients, but overall significantly affects the quality of life and activities of those afflicted. While most cases of CD are sporadic, emerging research has shown that a small number of cases of CD are genetic or familial, often caused by monogenic mutations that are autosomal dominantly inherited. Though the exact mechanism and effect these mutations have is still under investigation, these discoveries have allowed us to enhance our understanding of the disease pathology and open new avenues for targeted therapies. 

As mentioned, CD is defined as involuntary neck muscle contractions. It is the most common form of focal dystonia, a condition where muscle spasms affect a specific body region. The exact cause of cervical dystonia remains unclear, but research suggests a combination of genetic, environmental, and neurological factors. About 10-25% of cases have a familial link, with mutations commonly in genes such as DYT1, DYT6, DYT24, and DYT25. Most cases are generally sporadic, with possible triggers including physical trauma, infections, exposure to certain medications such as antipsychotics, or abnormalities in brain regions controlling movement. Symptoms of CD vary from patient to patient in terms of severity, but patients generally present with abnormal head postures, neck pain and stiffness, muscle hypertrophy and tremors. Clinical diagnostic procedures such as neurological examinations and electromyographies can be used to determine if a patient presents with CD. As for treating CD, while there is no cure, several treatments can help manage its symptoms, such as botox injections, oral medications in the form of muscle relaxants and anticholinergics, as well as physical therapy and rehabilitation. 

Genetic basis of familial cervical dystonia

CD can be characterised as either sporadic or familial, where multiple family members are affected, suggesting a genetic predisposition. While most cases are sporadic, approximately 10-25% show familial clustering, and some showing clear inheritance patterns. Cervical dystonia is generally heterogeneous, with both monogenic and polygenic influences. Some of the most well-characterised genes include DYT1, DYT6, DYT24, and DYT25. 

DYT1 mutations are caused by a deletion of 3 base pairs in the TOR1A gene which encodes torsinA. This mutation is responsible for the majority of childhood-onset generalised dystonia, with approximately 5% of carriers developing cervical dystonia. DYT6 mutations are caused by loss of function variants in THAP1 (a transcription factor) and result in mixed dystonia. DYT24 and DYT25 mutations both result in cervical dystonia, with DYT24 mutations resulting from missense variants in ANO3 (which is involved in calcium-activated chloride signalling), and DYT25 mutations resulting from heterozygous variants in GNAL (encoding a G-protein subunit). These mutations are generally autosomal-dominant inherited but with incomplete penetrance, i.e., not all individuals who inherit the disease-causing mutation will develop clinical symptoms. 

Diagnosis and treatment of cervical dystonia 

CD is clinically evaluated and diagnosed based on the presentation of a variety of symptoms. These include involuntary neck muscle contractions, which can cause abnormal postures, neck pain, tremors or sensory tricks, where there is temporary improvement with light touch. Neurological exams can be done to then rule out secondary causes such as Wilson’s disease, Parkinson’s or drug-induced dystonia. Other diagnostic tests can be used if needed, such as electromyographies to confirm abnormal muscle activity, MRI or CT scans, as well as genetic testing which is typically considered if there is a family history of CD, or if it was early onset. 

There are several treatments for CD, with the most common being botulinum toxin injections in the dystonic muscle of the neck. Other treatments include oral medications and deep brain stimulation. Botulinum toxin type A prevents the release of acetylcholine from the presynaptic axon of the motor end plate, which paralyses the dystonic muscle and provides relief from spasmodic torticollis for approximately 12-16 weeks. Deep brain stimulation to the basal ganglia and thalamus has been under trial for use in patients with CD, as a way to combat the abnormal tremors and muscle activities. Physical intervention such as mechanical braces or biofeedback, have also emerged as potential treatment options for CD, by providing stretching and strengthening exercises to aid the patient in keeping proper alignment of the head with the body. Certainly, while these techniques provide aid to the symptoms present in CD, further research is needed in providing targeted therapies and working towards a cure.

Summary

To summarise, cervical dystonia (CD), or spasmodic torticollis, is a neurological disorder characterised by involuntary muscle contractions in the neck, resulting in abnormal head postures, tremors, and pain. While most cases are sporadic, approximately 10-25% exhibit familial clustering, underscoring a significant genetic component. Key genes implicated in familial CD include TOR1A (DYT1), THAP1 (DYT6), ANO3 (DYT24), and GNAL (DYT25), which follow autosomal dominant inheritance with incomplete penetrance. This means not all mutation carriers develop symptoms, complicating genetic counseling and risk prediction. Diagnosis relies primarily on clinical evaluation, including identification of characteristic features such as sensory tricks that temporarily alleviate symptoms. Genetic testing is recommended for early-onset cases, familial clusters, or those with atypical presentations. Botulinum toxin injections remain the gold-standard treatment, targeting overactive muscles to reduce contractions and pain. Adjunctive therapies include oral medications (e.g., anticholinergics, muscle relaxants), physical therapy, and, for refractory cases, deep brain stimulation (DBS) targeting the globus pallidus internus. Recent research has elucidated pathogenic mechanisms, such as disruptions in synaptic vesicle recycling (TOR1A), calcium signaling (ANO3), and dopamine receptor coupling (GNAL). These insights are paving the way for targeted therapies, including gene-specific approaches and precision DBS programming. Despite advances, challenges remain, including variable expressivity, unknown environmental triggers, and the need for broader genetic screening.

In summary, cervical dystonia is a genetically heterogeneous disorder with evolving diagnostic and therapeutic landscapes. Multidisciplinary care, incorporating genetic insights and personalised treatment, is essential for optimising patient outcomes and quality of life.