DNA sequence analysis of SLC26A5, encoding prestin, in a patient-control cohort: identification of fourteen novel DNA sequence variations.

BACKGROUND: Prestin, encoded by the gene SLC26A5, is a transmembrane protein of the cochlear outer hair cell (OHC). Prestin is required for the somatic electromotile activity of OHCs, which is absent in OHCs and causes severe hearing impairment in mice lacking prestin. In humans, the role of sequence variations in SLC26A5 in hearing loss is less clear. Although prestin is expected to be required for functional human OHCs, the clinical significance of reported putative mutant alleles in humans is uncertain. METHODOLOGY/PRINCIPAL FINDINGS: To explore the hypothesis that SLC26A5 may act as a modifier gene, affecting the severity of hearing loss caused by an independent etiology, a patient-control cohort was screened for DNA sequence variations in SLC26A5 using sequencing and allele specific methods. Patients in this study carried known pathogenic or controversial sequence variations in GJB2, encoding Connexin 26, or confirmed or suspected sequence variations in SLC26A5; controls included four ethnic populations. Twenty-three different DNA sequence variations in SLC26A5, 14 of which are novel, were observed: 4 novel sequence variations were found exclusively among patients; 7 novel sequence variations were found exclusively among controls; and, 12 sequence variations, 3 of which are novel, were found in both patients and controls. Twenty-one of the 23 DNA sequence variations were located in non-coding regions of SLC26A5. Two coding sequence variations, both novel, were observed only in patients and predict a silent change, p.S434S, and an amino acid substitution, p.I663V. In silico analysis of the p.I663V amino acid variation suggested this variant might be benign. Using Fisher's exact test, no statistically significant difference was observed between patients and controls in the frequency of the identified DNA sequence variations. Haplotype analysis using HaploView 4.0 software revealed the same predominant haplotype in patients and controls and derived haplotype blocks in the patient-control cohort similar to those generated from the International HapMap Project. CONCLUSIONS/SIGNIFICANCE: Although these data fail to support a hypothesis that SLC26A5 acts as a modifier gene of GJB2-related hearing loss, the sample size is small and investigation of a larger population might be more informative. The 14 novel DNA sequence variations in SLC26A5 reported here will serve as useful research tools for future studies of prestin.

DNA sequence analysis of GJB2, encoding connexin 26: observations from a population of hearing impaired cases and variable carrier rates, complex genotypes, and ethnic stratification of alleles among controls.

Mutations in GJB2 are associated with hereditary hearing loss. DNA sequencing of GJB2 in a cohort of hearing impaired patients and a multi-ethnic control group is reported. Among 610 hearing impaired cases, 43 DNA sequence variations were identified in the coding region of GJB2 including 24 mutations, 8 polymorphisms, 3 unclassified variants (G4D, R127C, M163V), 1 controversial variant (V37I), and 7 novel variants (G12C, N14D, V63A, T86M, L132V, D159, 592_600delinsCAGTGTTCATGACATTC). Sixteen non-coding sequence variations were also identified among cases including the IVS1+1A>G mutation, 2 polymorphisms, and 13 novel variants. A diagnosis of GJB2-associated hearing loss was confirmed for 63 cases (10.3%). Heterozygous mutations were found in 39 cases (6.4%). Eleven cases carrying novel or unclassified variants (1.8 %) and 18 cases carrying the controversial V37I variant were identified (3%). In addition, 294 control subjects from 4 ethnic groups were sequenced for GJB2. Thirteen sequence variations in the coding region of GJB2 were identified among controls including 2 mutations, 6 polymorphisms, 2 unclassified variants (G4D, T123N), 1 controversial variant (V37I), and 2 novel variants (R127L, V207L). Nine sequence variations were identified among controls in the non-coding regions in and around GJB2 exon 2. Of particular interest among controls were the variability in carrier rates and ethnic stratification of alleles, and the complex genotypes among Asians, 47% of whom carried two to four sequence variations in the coding region of GJB2. These data provide new information about carrier rates for GJB2-based hearing loss in various ethnic groups and contribute to evaluation of the pathogenicity of the controversial V37I variant.

Outline of a medical genetics curriculum for internal medicine residency training programs.

To keep pace with the rapid advances in medical genetics, internal medicine residency training programs need to train internists to develop new attitudes, knowledge bases, and skill sets. Currently, such programs have no medical genetics curriculum. Thus, to set a minimum standard for genetics education in the context of training in internal medicine, the Internal Medicine Residency Training Program Genetics Curriculum Committee was formed, with members representing professional organizations of medical geneticists, internists, genetic counselors, internal medicine and genetics residency program directors, and internal medicine residents. The committee's task was to develop a concise outline of a medical genetics curriculum for residents in internal medicine in accordance with requirements of the Residency Review Committee for Internal Medicine of the Accreditation Council for Graduate Medical Education. The curriculum outline was drafted and circulated for comment. Before publication, the final document was approved by those member organizations that had a policy of approving curricula. Key learning objectives of the curriculum include appreciation of the rapid advances in genetics, the need for lifelong learning, the need for referral, and the role of genetic counselors and medical geneticists, as well as developing the ability to construct and analyze a three-generation pedigree. A wide variety of teaching methods can be useful in these regards, including didactic lectures, multimedia CD- ROMs, and clinical experience. Teaching should be related to clinical experiences whenever possible. The curriculum developed by the committee and presented in this article will assist in teaching residents the attitudes, knowledge, and skills they will require.

Do the genes that cause otosclerosis reduce susceptibility to otitis media?

HYPOTHESIS: The genetic factors that cause otosclerosis reduce susceptibility to otitis media. BACKGROUND: Susceptibility to some infectious diseases is modulated by host genetic factors. Genes that reduce the morbidity and mortality of infectious diseases may confer a selective advantage and achieve high-frequency in at-risk populations. Acute otitis media in the pre-antibiotic era frequently led to complications with high morbidity and mortality. The long-term sequela of acute otitis media is chronic otitis media. Chronic otitis media has a prevalence of 0.5 to 2 percent in the Caucasian population. Clinical otosclerosis occurs in 1 percent of Caucasians. Histologic otosclerosis occurs in 10 percent of Caucasians. MATERIALS AND METHODS: Retrospective analysis of 2,362 subjects with surgically confirmed otosclerosis. Subjects' medical records were reviewed for evidence of chronic otitis media. The incidence of chronic otitis media in the general population was compared with the subject population. RESULTS: Of the 2,362 subjects with surgically confirmed otosclerosis, one subject with evidence of chronic otitis media was identified. The incidence of chronic otitis media in the subject population is 0.04 percent (p < 0.0001). CONCLUSIONS: The incidence of chronic otitis media in subjects with a surgically confirmed diagnosis of otosclerosis is significantly lower than expected. The genes that cause otosclerosis may confer resistance to the pathogens that cause chronic otitis media and/or acute otitis media. The mechanism of resistance is unknown.

Genetic susceptibility to aminoglycoside ototoxicity: how many are at risk?

PURPOSE: To assess the occurrence of two mutations associated with susceptibility to aminoglycoside ototoxicity. METHODS: Genetic analysis of anonymized, residual diagnostic specimens. RESULTS: One occurrence of the A1555G mutation and seven occurrences of the 961delT + C(n) nucleotide change were found. Two previously unreported sequence changes, T961G and 956-960insC, were also found in six and five specimens, respectively. CONCLUSIONS: Genetic susceptibility to aminoglycoside ototoxicity may be more common than previously suspected. Further study of the 961delT + C(n) mutation is recommended to confirm its role in aminoglycoside ototoxicity and assess penetrance and variability with and without exposure to aminoglycoside antibiotics.