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Mohr-Tranebjaerg syndrome
This syndrome mostly affects males, causing early-onset hearing loss that worsens over time, followed by problems with movement (dystonia), and sometimes visual impairment. It is caused by changes in the TIMM8A gene and is inherited in an X-linked recessive manner.
Overview
Mohr-Tranebjaerg syndrome, also known as deafness-dystonia-optic atrophy syndrome, is a rare genetic disorder that primarily impacts the nervous system. Individuals with this condition typically experience a gradual loss of hearing starting in childhood, which then progresses to include difficulties with movement control and, in some cases, problems with vision. The syndrome is named after the doctors who first described it and is more commonly observed in males due to its X-linked inheritance pattern [PMID:19389248]. Females can be carriers and may experience milder symptoms or be asymptomatic.
Symptoms & clinical features
The initial and most consistent symptom of Mohr-Tranebjaerg syndrome is sensorineural hearing loss, which usually begins in childhood and gradually worsens, often leading to profound deafness. Following the onset of hearing loss, individuals typically develop dystonia, a movement disorder characterised by involuntary muscle contractions that cause repetitive or twisting movements and abnormal postures [PMID:19389248]. These movement difficulties often start in adolescence or early adulthood and can affect various parts of the body, including the limbs, trunk, and neck. Other neurological features can include speech difficulties (dysarthria), balance problems (ataxia), and intellectual disability, though the severity of these symptoms can vary widely. Some individuals may also develop optic atrophy, a condition affecting the optic nerve, which can lead to impaired vision.
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Affected organs
Mohr-Tranebjaerg syndrome predominantly affects the nervous system, including the brain, spinal cord, and cranial nerves. The inner ear is impacted, leading to sensorineural hearing loss. The basal ganglia, a group of structures deep within the brain involved in controlling movement, are also affected, contributing to the dystonia observed. The optic nerves, which transmit visual information from the eyes to the brain, can also be affected, leading to vision impairment in some cases. The condition is associated with issues in mitochondrial function, which are crucial for energy production in cells throughout the body, particularly in high-energy demand tissues like those in the nervous system [PMID:17968846].
Risks & severity
Mohr-Tranebjaerg syndrome is a progressive condition, meaning that symptoms tend to worsen over time. The sensorineural hearing loss typically begins in childhood and progresses to severe or profound deafness by adolescence. Dystonia usually manifests in adolescence or early adulthood, and its severity can vary significantly among affected individuals, ranging from mild to debilitating. Visual impairment due to optic atrophy may also develop, typically later than the hearing loss and dystonia. The exact prevalence of Mohr-Tranebjaerg syndrome is not well established, but it is considered a very rare condition. While the condition can significantly impact quality of life, affected individuals typically have a normal life expectancy. Females who are carriers of a pathogenic variant may experience milder symptoms such as hearing loss, but often remain asymptomatic [PMID:17968846].
Genetic causes
Mohr-Tranebjaerg syndrome is caused by pathogenic variants in the TIMM8A gene, located on the X chromosome. The TIMM8A gene provides instructions for making a protein called translocase of inner mitochondrial membrane 8A. This protein is part of a complex responsible for transporting other proteins into the inner membrane of mitochondria, which are the powerhouses of the cell. Pathogenic variants in TIMM8A disrupt this vital protein transport process, particularly affecting cells in the nervous system that rely heavily on mitochondrial function [PMID:17968846]. This disruption leads to impaired energy production and cellular dysfunction, resulting in the characteristic symptoms of the syndrome.
- TIMM8A translocase of inner mitochondrial membrane 8A
Inheritance pattern
Mohr-Tranebjaerg syndrome has an X-linked recessive inheritance pattern. This means the TIMM8A gene is located on the X chromosome, one of the two sex chromosomes. Males have one X and one Y chromosome, so if their single X chromosome carries a pathogenic variant in TIMM8A, they will develop the condition. Females have two X chromosomes; if one X chromosome carries a pathogenic variant, the other normal X chromosome can often compensate, leading to them being carriers. Female carriers typically do not show symptoms or may experience much milder features like hearing loss. An affected male will pass his X chromosome to all his daughters, making them carriers, but not to his sons. A female carrier has a 50% chance with each pregnancy of passing the pathogenic variant to her children; if a son inherits it, he will be affected, and if a daughter inherits it, she will be a carrier.
X-linked recessive: sons of a carrier mother have a 50% chance of being affected. Daughters have a 50% chance of being carriers.
Diagnosis & testing
Diagnosis of Mohr-Tranebjaerg syndrome is often suspected based on the characteristic combination of progressive hearing loss, developing dystonia, and sometimes optic atrophy, particularly in males. Confirmation of the diagnosis is typically achieved through genetic testing, which identifies pathogenic variants in the TIMM8A gene. Genetic testing for this condition is available in the UK through the NHS Genomic Medicine Service, often initiated following a referral to a clinical genetics service. The relevant R-codes for genetic testing would be determined by the clinical geneticist, depending on the specific clinical presentation and family history. Audiology assessments, neurological examinations, and ophthalmological evaluations are also important for characterising the clinical features.
Management & lifestyle
There is currently no cure for Mohr-Tranebjaerg syndrome, and management focuses on addressing the symptoms and improving quality of life. For hearing loss, hearing aids or cochlear implants can be beneficial, particularly when implemented early. Dystonia can be challenging to manage, but treatments may include medications such as anticholinergics or benzodiazepines, and sometimes botulinum toxin injections for specific muscle groups. Physiotherapy, occupational therapy, and speech therapy are crucial for maintaining mobility, independence, and communication. Regular follow-up with neurologists, audiologists, and ophthalmologists is important to monitor disease progression and adjust management strategies. Genetic counselling is also recommended for affected individuals and their families to understand the inheritance pattern and implications for future family planning within the NHS Genomic Medicine Service pathway.
UK care pathway
In the UK, individuals suspected of having Mohr-Tranebjaerg syndrome would typically be referred to a clinical genetics service by their GP or another specialist. Clinical geneticists work within the NHS Genomic Medicine Service (GMS) and can arrange appropriate genetic testing, often guided by specific R-codes from PanelApp UK. Following a diagnosis, ongoing care involves a multidisciplinary team, potentially including neurologists, audiologists, ophthalmologists, and therapists. Genetic counsellors are available to provide support and information about the condition, its inheritance, and implications for family members.
Frequently asked questions
What does X-linked recessive inheritance mean for my family?
X-linked recessive inheritance means the condition is caused by a gene on the X chromosome. Males are typically more severely affected because they only have one X chromosome. Females often carry the gene without showing symptoms or have milder ones, but they can pass it on to their children.
Will my hearing loss get worse over time with Mohr-Tranebjaerg syndrome?
Yes, the hearing loss associated with Mohr-Tranebjaerg syndrome is progressive. It typically begins in childhood and can worsen significantly over time, often leading to severe or profound deafness by adolescence or early adulthood.
Are there treatments for the movement problems in Mohr-Tranebjaerg syndrome?
While there isn't a cure, treatments can help manage the movement problems (dystonia). These may include various medications, botulinum toxin injections, and therapies such as physiotherapy and occupational therapy to help maintain function and reduce discomfort.
How is Mohr-Tranebjaerg syndrome diagnosed?
Diagnosis is usually confirmed by genetic testing, which identifies specific changes in the TIMM8A gene. This testing is often arranged by a clinical genetics service after considering the individual's symptoms and family history.
Can females be affected by Mohr-Tranebjaerg syndrome?
Females are typically carriers and often do not experience symptoms or have very mild ones, such as hearing loss, due to having two X chromosomes. However, in rare cases, females can experience symptoms similar to males, though often less severely.
References
- Adam MP, Bick S, Mirzaa GM. Deafness-Dystonia-Optic Neuronopathy Syndrome. 1993. PMID: 20301395
- Bahmad F Jr, Merchant SN, Nadol JB Jr. Otopathology in Mohr-Tranebjaerg syndrome. The Laryngoscope. 2007. PMID: 17471106
- Ventura I, Revert-Ros F, Revert F. A novel TIMM8A mutation in Mohr-Tranebjaerg syndrome without hearing loss and with basal ganglia iron deposition. Orphanet journal of rare diseases. 2025. PMID: 40597358
- Rendtorff ND, Karstensen HG, Lodahl M. Identification and analysis of deletion breakpoints in four Mohr-Tranebjærg syndrome (MTS) patients. Scientific reports. 2022. PMID: 36056138
- Wang H, Wang L, Yang J. Phenotype prediction of Mohr-Tranebjaerg syndrome (MTS) by genetic analysis and initial auditory neuropathy. BMC medical genetics. 2019. PMID: 30634948
- Huang Y, Chen Z, Deng W. CHCHD2 rescues the mitochondrial dysfunction in iPSC-derived neurons from patient with Mohr-Tranebjaerg syndrome. Cell death & disease. 2025. PMID: 40075073
- Merchant SN, McKenna MJ, Nadol JB Jr. Temporal bone histopathologic and genetic studies in Mohr-Tranebjaerg syndrome (DFN-1). Otology & neurotology : official publication of the American Otological Society, American Neurotology Society [and] European Academy of Otology and Neurotology. 2001. PMID: 11449109
- Sousa E, Abreu M, Tkachenko N. Case report: Mohr-Tranebjaerg syndrome: hearing impairment as the onset of an insidious disorder with high recurrence risk. Frontiers in neurology. 2023. PMID: 37325222