Abnormal pinna type and hearing loss correlations in Down's syndrome.

Significant hearing loss and external pinna malformations are two of the most common defects evident in Down's syndrome. The external and middle ears are linked embryologically, both arising from the first and second branchial arches. Evidence indicates that the majority of hearing loss in Down's syndrome is conductive in nature, originating from malformations of the middle ear ossicles and/or the eustachian tube. Recent studies also have indicated that hearing loss is a contributing factor to the IQ and learning deficits that afflict most individuals with Down's syndrome. Therefore, an early, external diagnostic feature for predicting conductive hearing loss would be desirable. In the current study, people with Down's syndrome, people with non-Down's mental retardation and control subjects were examined in a clinical environment for the presence of hearing loss and pinna defects. It was found that 90% of the Down's syndrome population had significant hearing loss, compared to slightly more than 50% in the non-Down's group and no hearing loss in the controls. Also, the majority of hearing loss among individuals with Down's syndrome was conductive, while all hearing loss in the non-Down's group was sensorineural. The Down's syndrome population exhibited nearly 3.5 pinna defects per ear, with malformations of the helix being very evident. The non-Down's population exhibited 2.5 pinna defects per ear, with concha defects being the most common.

Effects of the microphthalmic white gene on audiogenic seizure susceptibility in mice.

Audiogenic seizure susceptibility was studied in mice segregating for the microphthalmic white gene (Miwh). Previous work by Deol had indicated that mice with either one or two Miwh alleles had severe inner ear defects. A congenic inbred strain provided mice that were identical in genetic background except for single-gene substitutions at the microphthalmia locus. The three genotypes tested were Miwh/Miwh, Miwh/+, and +/+. Mice were exposed to the sound stimulus once for a 1-min period between the ages of 17 and 30 days. Heterozygous Miwh/+ mice had more seizures and were more reactant than either type of homozygote at all ages tested. Responses were low at 17 days of age, peaked sharply by 23 days, and declined markedly by 30 days.

ECoG results in perilymphatic fistula: clinical and experimental studies.

Patients with perilymphatic fistula have been described as having symptoms similar to Meniere's disease and endolymphatic hydrops. Direct clinical or experimental evidence linking the two inner ear disorders has been lacking. An enhancement of the summating potential observed with electrocochleography suggests a diagnosis of ELH in both of these inner ear disorders. In this study, ECoG results of 27 patients with surgically confirmed PLF are reported. Fourteen patients with surgically confirmed spontaneous PLF had abnormal ECoG. Six of these 14 patients had normal hearing. The ECoG changes in patients with Meniere's disease and those with surgically confirmed PLF are identical, indicating the underlying pathologic change in both is hydrops. But there is no specific diagnostic abnormality on ECoG that differentiates these two inner ear disorders. Also, an experimental model of PLF was developed and studied in guinea pigs. "Inactive" PLF is defined as "an opening was made into the cochlea, but if no perilymph moved out through the fistula, it was defined as inactive" An "active" PLF occurs when perilymph actually moves from the inner ear out to the middle ear. ECoGs were recorded before and after creation of an "active" PLF. ECoG abnormalities were seen in "active" PLF and correlated with histologic data demonstrating ELH. An abnormally enhanced summating potential was demonstrated after active removal of perilymph through the experimentally created fistula. Cochlear duct histology showed hydropic distention of Reissner's membrane in the experimental ears and no changes in the membranous labyrinths of the unoperated, control ears.(ABSTRACT TRUNCATED AT 250 WORDS)