Hereditary deafness syndromes with onset in adult life

Morphometric study of the anteroventral cochlear nucleus of two mouse models of presbycusis

The dimensions and volume of the anterior ventral cochlear nucleus (AVCN), the density and number of AVCN neurons, and the size of neuronal somata nuclei (in Nissl-stained tissue) were determined in two mouse models of age-related hearing loss: the C57BL/6J strain, which undergoes progressive chronic sensorineural hearing loss with onset during young adulthood, and the CBA/J, which demonstrates only moderate hearing loss with onset late in life. Frontal and horizontal AVCN sections, as well as cochleas, were analyzed in 4 C57 age-groups (1, 7, 12, 19+ months) and in 3 CBA groups (1, 10, 22 months). Within each strain no significant changes in AVCN dimensions or volume occur with aging. In C57 mice, packing density and cell number decrease between 1 and 7 months, but remain stable thereafter, despite chronic severe hearing impairment. CBA mice show a reduction in AVCN cell number and packing density only during the second year of life. In aging C57 mice, the size of spherical and perhaps globular cells increases, whereas the size of multipolar cells tends to decrease slightly. In CBA mice, all three AVCN cell types tend to decrease in size with aging. The early cell loss and cell size increases in C57 mice are most consistent in the dorsal (high frequency) region of the AVCN. Likewise, loss of cochlear spiral ganglion cells is most pronounced in the base of the cochlea, which provides input to this region. The data indicate that aging is associated with rather different central effects, depending on AVCN cell type, cochleotopic organization, genotype, and/or the type of peripheral hearing loss involved. The C57 and CBA AVCNs also differ in several aspects irrespective of age. The volume of AVCN and number of AVCN neurons are significantly greater in C57 mice.

Clinical findings and diagnostic problems in sensorineural low frequency hearing loss

The otological and audiological findings in 39 patients with sensorineural low frequency hearing loss are reported. This type of perceptive hearing loss is difficult to distinguish from the true conductive hearing losses due to the air conduction audiogram shape and the invalidity of bone conduction determinations showing a false "air-bone gap". This may lead to surgical treatment of a perceptive hearing loss, as reported in the four case histories. By various audiological tests, contradictory information may be obtained. In our material, Bing's test and absent acoustic reflexes indicated a conductive disorder in 25% of the ears. The final differentiation may require cochleography. The hearing loss may be diagnosed as Meniere's disease. In our material only 17% complained of tinnitus and no patients had vertigo. Consequently, we find sensorineural low frequency hearing loss to differ from Meniere's disease. Our material comprises different etiological types of perceptive low frequency hearing loss. On type was inherited as an autosomal dominant trait, another type due to cochlear malformation probably also inherited, and a third group showing diverse audiological results. When the diagnosis is established, the patients may be treated successfully by specially constructed hearing aids.

Reliability of Békésy threshold tracing in identification of carriers of genes for an X-linked disease with deafness

Seven identified carriers and 20 potential carriers of Norris's disease have been examined by pure tone octave audiometry and Békésy audiometry. The investigation supports earlier results of Békésy threshold tracings performed in heterozygote carriers of genes for recessive hearing impairment. The sensitivity of the method is poor. The specificity of the Békésy threshold tracing is high, meaning that an absent dip cannot exclude the possibility of a subject being a carrier, whereas a present dip can be regarded as an indication of carrier. When comparing conventional octave audiometry and Békésy threshold tracing, the latter method is found to be more subtle in finding carriers of genes for recessive deafness. Therefore, Békésy threshold tracing may be of help in the genetic counselling of potential carriers of genes for recessive deafness.

Menière's disease in childhood

Two cases of Menière's disease in childhood were found during one year from 850 examinations of children. The clinical and audiological findings are similar to those seen in adults.

Hereditary progressive sensorineural deafness

Progressive sensorineural hearing losses found in seven members of three families are presented. Genetic transmission patterns in the study appeared to be autosomal dominant in two families and recessive in one family. The common audiological features of these cases include bilaterally symmetrical audiometric configuration and fairly good speech discrimination. The hearing losses of most of the cases appeared to begin at high frequencies progressing later to involve lower frequencies. The main histopathological changes in the temporal bones of one of the cases were degeneration of the organ of Corti and of the spiral ganglion in the lower cochlear coils and cystic degeneration of the stria vascularis in the upper coils.