A simple and reliable method for the detection of the 30delG mutation of the CX26 gene

New criteria of indication and selection of patients to cochlear implant

Numerous changes continue to occur in cochlear implant candidacy. In general, these have been accompanied by concomitant and satisfactory changes in surgical techniques. Together, this has advanced the utility and safety of cochlear implantation. Most devices are now approved for use in patients with severe to profound unilateral hearing loss rather then the prior requirement of a bilateral profound loss. Furthermore, studies have begun utilizing short electrode arrays for shallow insertion in patients with considerable low-frequency residual hearing. This technique will allow the recipient to continue to use acoustically amplified hearing for the low frequencies simultaneously with a cochlear implant for the high frequencies. The advances in design of, and indications for, cochlear implants have been matched by improvements in surgical techniques and decrease in complications. The resulting improvements in safety and efficacy have further encouraged the use of these devices. This paper will review the new concepts in the candidacy of cochlear implant. Medline data base was used to search articles dealing with the following topics: cochlear implant in younger children, cochlear implant and hearing preservation, cochlear implant for unilateral deafness and tinnitus, genetic hearing loss and cochlear implant, bilateral cochlear implant, neuropathy and cochlear implant and neural plasticity, and the selection of patients for cochlear implant.

Cochlear implantation in common forms of genetic deafness

Genetic factors are among the main etiologies of severe to profound hearing loss and may play an important role in cochlear implantation (CI) outcomes. While genes for common forms of deafness have been cloned, efforts to correlate the functional outcome of CIs with a genetic form of deafness carried by the patient have been largely anecdotal to date. It has been suggested that the differences in auditory performance may be explained by differences in the number of surviving spiral ganglion cells, etiology of hearing loss, and other factors. Knowledge of the specific loci and mutations involved in patients who receive cochlear implants may elucidate other factors related to CI performance. In this review article, current knowledge of cochlear implants for hereditary hearing loss will be discussed with an emphasis on relevant clinical genotype-phenotype correlations.

The use of buccal smears for a non-invasive screening of the 35delG mutation of the Connexin-26 gene in hearing impaired young children

OBJECTIVES

Recent advances in genetic research indicate that about 50% of congenital deaf patients have a genetic background, with mutations in the Connexin-26 gene being the most frequent one. Screening methods for the genetic cause of deafness have so far mostly been based on the use of peripheral whole blood as DNA source. The use of buccal smears for the genetic screening of deaf patients presents an interesting alternative to drawing blood, especially in young children. In order to validate this method, we compared results from buccal smears from very young deaf children (age<or=3 years) and deaf patients older than 3 years with the results from blood samples deriving from the same patients.

METHODS

The detection of the 35delG mutation in the Connexin-26 gene was chosen to demonstrate the method's feasibility. Blood and buccal smears were collected for genetic analysis from 29 very young deaf children (Group 1: age<or=3 years) and 31 deaf patients older than 3 years (Group 2) during their clinical pre-evaluation for cochlear implantation. Genomic DNA was isolated from blood as well as from buccal smears. Yield of both sources was determined by photometric evaluation of the isolated DNA concentration. Genomic DNA isolated from blood and buccal smears was then submitted to PCR-mediated site-directed mutagenesis followed by BS1 YI restriction and electrophoresis. The results for 35delG detection in DNA originating from blood were compared to those of buccal smears.

RESULTS

Quantitative DNA analysis showed that both sources provided adequate amounts of DNA for PCR. No significant difference was found between Group 1 and Group 2 considering either the DNA amount isolated from blood or from buccal smears. In all 60 patients, DNA isolated from blood revealed the same results concerning the presence of the 35delG mutation as DNA originating from buccal smears.

CONCLUSIONS

This study demonstrates that buccal smears are an adequate, reliable source of genomic DNA providing material for genetic tests that can especially help to avoid drawing blood from very young children for the genetic screening of deafness.

Sandwich hybridisation assay for quantitative detection of yeast RNAs in crude cell lysates

BACKGROUND: A rapid microtiter plate based sandwich hybridization assay was developed for detection and quantification of single RNA species using magnetic beads. Following solution hybridization target RNA molecules were collected by biotin-streptavidin affinity binding and detected by fluorescence signal generated by alkaline phosphatase. The 18S rRNA and SUC2 mRNA of Saccharomyces cerevisiae were used as model RNA target molecules. RESULTS: The sensitivity of the assay was approximately 1.2 x 109 (2 fmol) molecules of target RNA. The developed method was feasible with crude cell lysates of S. cerevisiae carlsbergensis and was evaluated by measuring the levels of 18S rRNA during cell growth and SUC2 mRNA under repressive and inductive conditions. The 18S rRNA expression level followed the changes in the specific growth rate. SUC2 mRNA levels were in good correlation with the measured invertase enzyme activities. CONCLUSIONS: The here presented sandwich hybridisation method was succefully applied for monitoring the amounts of ribosomal RNA and mRNA with high expression level in shake flask cultivation conditions. Sandwich hybridisation method offers a fast and convenient tool for following single key RNA species of interest in the production conditions.

Connexin 26 mutations in cases of sensorineural deafness in eastern Austria

Mutations in the connexin 26 (Cx26) gene (GJB2) are associated with autosomal nonsyndromic sensorineural hearing loss. This study describes mutations in the Cx26 gene in cases of familial and sporadic hearing loss (HL) by gene sequencing and identifies the allelic frequency of the most common mutation leading to HL (35delG) in the population of eastern Austria. For this purpose we have developed and applied a molecular beacon based real-time mutation detection assay. Mutation frequencies in the Cx26 gene of individuals from affected families (14 out of 46) and sporadic cases (11 out of 40) were 30.4% and 27.5%, respectively. In addition to known disease related alterations, a novel mutation 262 G-->T (A88S) was also identified. 35delG accounted for almost 77% of all Cx26 mutations detected and displayed an allelic frequency in the normal hearing population of 1.7% (2 out of 120). The high prevalence of the 35delG mutation in eastern Austria would therefore allow screening of individuals and family members with Cx26 dependent deafness by a highly specific and semi-automated method.

Genetics and molecular biology of deafness. Update

This article discusses the latest research in the molecular biology and genetics of hearing impairment and its importance to otolaryngologists. Recent research has led to the discovery of many of the genes and gene products that are responsible for hereditary hearing impairment. State mandated screening of newborn infants for hearing loss ensures that a large number of hearing-impaired children will be detected at a very early age. Additionally, these children often will be referred to the otolaryngologist for evaluation of the hearing impairment. It is the otolaryngologist who must gather a detailed family history and perform a thorough physical examination to fully assess the cause of the hearing impairment. In taking the family history, it is important to note that the diagnosis of a hereditary hearing impairment often involves the evaluation of a large-sized family that has a history of hearing disorders. A history of an affected individual in a small family does not necessarily support a diagnosis of hearing impairment in later affected offspring because of the small sample size. Often, a hearing impairment that is part of a syndrome may not be detected because the physical findings associated with a syndrome are subtle in a young infant. For example, the white forelock seen in patients with Waardenburg's syndrome type I cannot be visualized in the infant who lacks hair. Additionally, some patients with syndromic hearing impairment do not present with physical findings, but rather they exhibit abnormal laboratory studies. Additional points to remember include the following: As infectious iatrogenic causes of hearing impairment decrease, the relative incidence of hereditary hearing impairment will increase. Hereditary hearing impairment can present as an isolated finding, or in association with a number of anomalies recognizable as a syndrome. The study of genetics and molecular biology has led to the identification of genes associated with hearing impairment and will allow for future screening and possible therapy for the hearing-impaired. The screening of newborns for hearing impairment using the techniques of molecular biologists and geneticists will result in early identification and appropriate intervention for those at risk for hereditary hearing impairment. An understanding of the syndromic and nonsyndromic causes of hereditary hearing impairment can help the otolaryngologist make a diagnosis and provide appropriate audiologic and educational management to the patient.

Rapid detection of Campylobacter fetus by polymerase chain reaction combined with non-radioactive hybridization using an oligonucleotide covalently bound to microwells

Campylobacter fetus is recognized as a human and animal pathogen. The isolation and differentiation of C. fetus in diagnostic laboratories is hindered by its relatively slow growth and lack of distinguishing biochemical characteristics. We cloned and sequenced a 1581-bp DNA fragment, IG02, isolated from a C. fetus genomic library. This fragment was used as a probe on DNAs extracted from C. fetus strains and other Campylobacter species: IG02 hybridized only with DNAs from C. fetus strains. A PCR-based test was developed for the detection of C. fetus. A pair of oligonucleotide primers was designed to amplify a 141-bp fragment of IG02. The amplified product was analysed by a non-radioactive sandwich hybridization in microtiter plate using a capture oligonucleotide and a biotin-labelled oligonucleotide for the detection. The combination of PCR and non-radioactive microplate hybridization is a convenient method for the rapid detection of C. fetus.