Minimally invasive genetic screen for GJB2 related deafness using dried blood spots.

OBJECTIVE: Nonsyndromic hearing loss is one of the most abundant human sensory disorders, and can be found in 1 out of 1000 newborns. In 60-70% of the cases this disorder is hereditary. The phenotype varies from moderate hearing loss to almost complete deafness, often only revealed in late childhood. Early detection of hearing related genetic variations in the first few weeks of life would allow planning of the audiological and logopedical procedures to maintain the children's normal audiological and speech development, and if required a cochlear implantation can be planned in time. We wanted to evaluate, whether the blood samples collected from neonates onto Guthrie cards (dried blood spots, or DBS), and blood collected from people of various ages into blood collecting tubes is equally usable for genetic testing. The quality of the samples on DBS's for genetic tests after an extended period of storage was evaluated. The methods for sample preparation and analysis were also evaluated. METHODS: Two DNA extraction methods were compared on the samples. We extracted DNA from whole blood with the Versagene Blood Kit from Gentra, and from DBS's with boiling. Allele-specific PCRs (AS-PCR) were carried out on each sample. Samples were analyzed with AS-PCR and sequencing, for the 35delG mutation in the GJB2 (Cx26) gene. Freshly drawn and dried blood spot samples stored for several years were used in the experiments. RESULTS: An AS-PCR method for detecting 35delG mutation on DNA extracted from Guthrie cards was validated. Blood samples up to 10 years of storage were applicable in the screen. 84 patients were found with 35delG mutations, both heterozygous (with no detected hearing related phenotypical discrepancies), and homozygous (phenotipically with moderate to severe hearing loss) forms. CONCLUSIONS: The dried blood spots on Guthrie cards require only three drops of blood to be collected from children, which causes less stress than taking 3 ml of blood. The blood stored on Guthrie cards can be used to store DNA samples for at least 10 years. Even under suboptimal storage conditions the samples' DNA remains intact for genetic testing. Compared to blood collection tubes Guthrie cards cost less, are easier to transport and store.

Neural response telemetry in cochlear implant users.

Programming of multichannel cochlear implants requires subjective responses to a series of sophisticated psychophysical percepts. It is often difficult for cochlear implant patients (especially young prelinguistically deaf children) to provide adequate responses for device fitting. However, the neural response telemetry (NRT) system renders possible the measurement of the compound action potential threshold. We performed NRT examinations in 27 cochlear implant users with Nucleus 24-channel cochlear implants. Measurements were obtained from five electrodes (3, 5, 10, 15, and 20) in each patient. Our goal was to look for correlation between behavioral subjective thresholds and compound action potentials. The action potentials could be elicited in 23 patients in all measured electrodes. The NRT threshold values were highly correlated with electrical threshold levels obtained through subjective responses. Our results suggest that the electrically elicited neural responses may yield very important information for device fitting in patients with cochlear implants.

Effects of noise on the intensity of distortion product otoacoustic emissions.

Distortion product otoacoustic emission (DPOAE) is a widely used differential diagnostic method for diagnosing inner ear disorders. It provides us information on the condition of the outer hearing cells (OHCs). Otoacoustic emission occurs only when the OHCs are functioning normally. Changes in thresholds of DPOAE curves can provide us important information on the activity of the OHCs. The inner ear shows nonlinear properties if the OHCs are functioning normally. If OHCs are injured and thus function improperly, the system stops showing nonlinear properties. If we have a system with periodic excitation and, with the addition of white noise, the signal-to-noise ratio on the output increases (at least for small noise intensities), we have witnessed what is called phenomenon stochastic resonance. Our goal was to elucidate how white noise influences the intensity of DPOAE. If there is emission, that specific ear surely exhibits nonlinear behavior, which in turn is the basic property needed for stochastic resonance.