Abstract
BackgroundThirty thousand infants are born every year with congenital hearing impairment in mainland China. Racial and regional factors are important in clinical diagnosis of genetic deafness. However, molecular etiology of hearing impairment in the Tibetan Chinese population living in the Tibetan Plateau has not been investigated. To provide appropriate genetic testing and counseling to Tibetan families, we investigated molecular etiology of nonsyndromic deafness in this population.MethodsA total of 114 unrelated deaf Tibetan children from the Tibet Autonomous Region were enrolled. Five prominent deafness-related genes, GJB2, SLC26A4, GJB6, POU3F4, and mtDNA 12S rRNA, were analyzed. Inner ear development was evaluated by temporal CT. A total of 106 Tibetan hearing normal individuals were included as genetic controls. For radiological comparison, 120 patients, mainly of Han ethnicity, with sensorineural hearing loss were analyzed by temporal CT.ResultsNone of the Tibetan patients carried diallelic GJB2 or SLC26A4 mutations. Two patients with a history of aminoglycoside usage carried homogeneous mtDNA 12S rRNA A1555G mutation. Two controls were homozygous for 12S rRNA A1555G. There were no mutations in GJB6 or POU3F4. A diagnosis of inner ear malformation was made in 20.18% of the Tibetan patients and 21.67% of the Han deaf group. Enlarged vestibular aqueduct, the most common inner ear deformity, was not found in theTibetan patients, but was seen in 18.33% of the Han patients. Common molecular etiologies, GJB2 and SLC26A4 mutations, were rare in the Tibetan Chinese deaf population.ConclusionThe mutation spectrum of hearing loss differs significantly between Chinese Tibetan patients and Han patients. The incidence of inner ear malformation in Tibetans is almost as high as that in Han deaf patients, but the types of malformation vary greatly. Hypoxia and special environment in plateau may be one cause of developmental inner ear deformity in this population.
Highlights
Hereditary hearing loss is a genetically heterogeneous disorder in humans, with an incidence rate of approximately 1 in 1000 children [1]
The majority of cases of hereditary hearing loss are caused by nuclear gene defects, it has become clear that mutations in mitochondrial DNA can cause nonsyndromic hearing loss
None of the Tibetan patients with hearing impairment in our study showed any sign of vestibular dysfunction in their case history
Summary
Hereditary hearing loss is a genetically heterogeneous disorder in humans, with an incidence rate of approximately 1 in 1000 children [1]. In China, there are 27.80 million people with hearing and speech disabilities; of these, 20.04 million have simple hearing disability [3], with genetic factors accounting for about 55% of the Chinese deaf population of Han ethnicity [3,4]. The most common causes of nonsyndromic autosomal recessive hearing loss are mutations in connexin 26, a gap-junction protein encoded by the GJB2 gene [5,6,7,8,9,10,11,12,13]. The majority of cases of hereditary hearing loss are caused by nuclear gene defects, it has become clear that mutations in mitochondrial DNA (mtDNA) can cause nonsyndromic hearing loss. Molecular etiology of hearing impairment in the Tibetan Chinese population living in the Tibetan Plateau has not been investigated. To provide appropriate genetic testing and counseling to Tibetan families, we investigated molecular etiology of nonsyndromic deafness in this population
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