Category: Illness or disabilities
Introduction and description
Mohr-Tranebjaerg syndrome (MTS) is an X-linked, recessive, syndromic sensorineural hearing loss (HL) characterized by onset of deafness in childhood followed later in adult life by progressive neural degeneration affecting the brain and optic nerves.
Mohr-Tranebjaerg syndrome (MTS) is not only characterized by deafness, brain damage and blindness, but also dystonia.
Dystonia is a neurological movement disorder syndrome in which sustained or repetitive muscle contractions result in twisting and repetitive movements or abnormal fixed postures. The movements may resemble a tremor.
Profound hearing impairment often develops by infancy and precedes the development of dystonia, which varies in time of onset from the first to the sixth decades, with a peak in the second and third decades. “Dystonia in MTS tends to be focal, segmental, or multifocal in distribution at onset, with a predilection for the upper body, variably involving the head, neck, and upper limbs. The majority of patients have progression or generalization of their dystonia regardless of age of onset. “
Associated features include progressive cognitive decline, pyramidal signs, and gait freezing and postural instability, all of which tend to indicate various forms of brain damage.
Optic atrophy and cortical visual impairment are also observed. So the person gradually loses their sight.
OBJECTIVES: To describe the otologic presentation and temporal bone histopathology in four affected individuals with MTS.
MATERIAL AND METHODS: All four subjects belonged to a large, multigenerational Norwegian family and were known to carry a frame shift mutation in the TIMM8A gene. Temporal bones were removed at autopsy and studied by light microscopy. Cytocochleograms were constructed for hair cells, stria vascularis, and cochlear neuronal cells. Vestibular neurons were also counted.
RESULTS: All four subjects developed progressive HL in early childhood, becoming profoundly deaf by the age of 10 years. All four developed language, and at least one subject used amplification in early life. Audiometric evaluation in two subjects showed 80- to 100-dB HL by the age of 10 years. The subjects died between the ages of 49 and 67. The otopathology was strikingly similar in that all bones examined showed near-total loss of cochlear neuronal cells and severe loss of vestibular neurons. When compared with age-matched controls, there was 90% to 95% loss of cochlear neurons and 75% to 85% loss of vestibular neurons.
CONCLUSIONS: We infer that the HL in MTS is likely to be the result of a postnatal and progressive degeneration of cochlear neurons and that MTS constitutes a true auditory neuropathy. Our findings have implications for clinical diagnosis of patients with MTS and management of the HL. PMID: 17471106
MTS is caused by mutations in the DDP/TIMM8A gene, which encodes for a 97 amino acid polypeptide; this polypeptide is a translocase of the inner mitochondrial membrane.
There have been people found with this disorder who have more mutations than those above “We report clinical, neurophysiological, and ophthalmological data on 6 subjects from 3 Australian kindreds, including 2 with novel mutations”.
But, the cause of the mutation is not known, and it is this that is key, however, please see the more general section on inherited disease, as we believe the cause can be found in this section.
References and further reading
Laryngoscope. 2007 Jul;117(7):1202-8. Otopathology in Mohr-Tranebjaerg syndrome. Bahmad F Jr1, Merchant SN, Nadol JB Jr, Tranebjaerg L. 1Department of Otolaryngology, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts 02114-3096, USA.