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Audiological and Vestibular Findings in Subjects with MELAS Syndrome
Dan Dupont Hougaard1, Danial Hofgaard Hestoy2, Allan Thomas Hojland3
1Department of Otolaryngology, Head - Neck Surgery and Audiology, Aalborg University Hospital, Aalborg, Denmark;Department of Clinical Medicine, Aalborg University School of Medicine, Denmark.
Objectives:
The mitochondrial DNA (mtDNA) point mutation m.3243A>G is known to express the following two syndromes among others: maternally inherited diabetes and deafness (MIDD) and mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS). Sensorineural hearing loss (SNHL) is the most frequent symptom in individuals harboring the m.3243A>G mutation. However, dysfunction of the vestibular organs has been scarcely examined. Therefore, the present study aimed to study the impact of the m.3243A>G mutation on the inner ear.
Materials And Methods:
A total of 8 subjects harboring the blood-verified m.3243A>G mutation underwent thorough audiological and vestibular examinations, including tone and speech audiometry, video head impulse test (vHIT), ocular and cervical vestibular-evoked myogenic potential (oVEMP and cVEMP), and full otoneurological examination. The subjects also answered a Dizziness Handicap Inventory (DHI) questionnaire.
Results:
SNHL was identified in all the 8 subjects, with a mean pure-tone average-4 (PTA-4) of 59 dB. Speech discrimination score (n=7) ranged from 24% to 100% (mean 74%), and vHIT (n=42) detected pathology in nine lateral semicircular canals (SCCs), five posterior SCCs, and one anterior SCC, whereas three measurements were inconclusive. All oVEMPs (n=14 ears) were absent, nine cVEMPs were absent, and two were inconclusive. Based on the DHI scores, 6 subjects reported none to mild dizziness, 1 reported moderate, and 1 reported severe dizziness.
Conclusion:
Our study population had pathological findings from every audiological and vestibular end organs. The results indicated that the pathological findings originated from within the end organs themselves and not within the superior and inferior vestibular or cochlear nerve.
Insights
The m.3243A>G mitochondrial DNA mutation causes sensorineural hearing loss and affects vestibular organs. This study found inner ear dysfunction in all subjects with this mutation.
Area of Science:
- Genetics and Molecular Biology
- Neuroscience
- Otolaryngology
Background:
- The mitochondrial DNA (mtDNA) point mutation m.3243A>G is associated with maternally inherited diabetes and deafness (MIDD) and mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS).
- Sensorineural hearing loss (SNHL) is a common symptom, but vestibular organ function in individuals with this mutation is poorly understood.
Purpose of the Study:
- To investigate the impact of the m.3243A>G mutation on the inner ear, specifically examining audiological and vestibular function.
- To determine if the observed pathologies originate from the end organs or the vestibular/cochlear nerves.
Main Methods:
- Eight subjects with the m.3243A>G mutation underwent comprehensive audiological and vestibular assessments.
- Evaluations included pure-tone and speech audiometry, video head impulse test (vHIT), ocular and cervical vestibular-evoked myogenic potentials (oVEMP and cVEMP), and a Dizziness Handicap Inventory (DHI) questionnaire.
Main Results:
- All 8 subjects exhibited SNHL (mean PTA-4 of 59 dB).
- Vestibular examinations revealed significant pathology in semicircular canals (SCCs) via vHIT, and absent oVEMPs and cVEMPs in most subjects.
- Dizziness Handicap Inventory scores indicated that 6 out of 8 subjects experienced none to mild dizziness.
Conclusions:
- The m.3243A>G mutation leads to pathological findings in all audiological and vestibular end organs.
- Evidence suggests the pathologies are intrinsic to the end organs, not caused by damage to the vestibular or cochlear nerves.
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