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

Connexin 26 and 30 genes mutations in patients with chronic rhinosinusitis

OBJECTIVES

Connexin proteins play an important role in cell-to-cell communication. Mutations in the genes that encode for these connexins may potentially lead to dysfunction in mucociliary clearance predisposing to chronic rhinosinusitis (CRS) or recurrent acute rhinosinusitis (RARS). The objective of this study was to assess for the presence of connexin 26 and 30 gene mutations in patients with CRS and RARS.

STUDY DESIGN

Prospective case series.

METHODS

Forty-six consecutive patients who were diagnosed with CRS or RARS at a single tertiary care facility were included in the study. Patients with known dysfunction in mucociliary clearance were excluded. The following clinical data were collected: age, gender, duration of disease and age at onset, personal history of otitis media and/or sensorineural hearing loss (SNHL), and family history of paranasal sinus disease and SNHL. Buccal swab deoxyribonucleic acid (DNA) specimens were sequenced for connexin 26 and 30 genes.

RESULTS

The study group consisted of 32 females and 14 males, 8 children and 38 adults. Adequate sequencing of connexin 30 gene was possible in all 46 specimens, but in only 19 specimens for connexin 26 gene. Connexin 30 gene mutations were not detected in any of the 46 specimens. Two of the 19 specimens had heterozygous mutations in the connexin 26 gene; there was one V371 mutation and one 35dG mutation. Both patients were adults; the patient with 35dG mutation had SNHL.

CONCLUSION

Mutations in connexin 26 and 30 genes are rare in patients with CRS or RARS and do not seem to play a contributory role in the pathogensis of these disorders.

Screening for gap junction protein beta-2 gene mutations in Malays with autosomal recessive, non-syndromic hearing loss, using denaturing high performance liquid chromatography

OBJECTIVE

To determine the frequency and type of gap junction protein beta-2 gene mutations in Malay patients with autosomal recessive, non-syndromic hearing loss.

METHODS

A total of 33 Malay patients with autosomal recessive, non-syndromic hearing loss were screened for mutations in the Cx26 coding region. Deoxyribonucleic acid was extracted from buccal swab samples and subjected to polymerase chain reaction. Slow-reannealing was performed, followed by screening using denaturing high performance liquid chromatography.

RESULTS

Eight of the samples (24.2 per cent) showed heterozygous peaks, and further sequencing of these samples revealed four patients (50.0 per cent) with the W24X mutation, two (25.0 per cent) with the V37I mutation and another two (25.0 per cent) with the G4D mutation.

CONCLUSIONS

Analysis of buccal swab samples by denaturing high performance liquid chromatography is noninvasive and suitable for rapid and reliable screening of gap junction protein beta-2 gene mutations in patients with autosomal recessive, non-syndromic hearing loss. Malay patients with autosomal recessive, non-syndromic hearing loss have different kinds of gap junction protein beta-2 gene mutations which are rarely found in other populations.

The prevalence of the 235delC GJB2 mutation in a Chinese deaf population

PURPOSE

Mutations in the GJB2 gene are the most frequently found mutations in patients with nonsyndromic hearing impairment in populations studied to date. However, the prevalence of mutations varies among different ethnic groups. In most areas of China, genetic testing for nonsyndromic hearing impairment is currently not available because of the lack of information regarding the molecular cause of nonsyndromic hearing impairment. The purpose of this study is to determine the prevalence of a common GJB2 mutation, 235delC, in Chinese deaf children.

METHODS

We collected DNA specimens from 3004 patients with nonsyndromic hearing impairment from 26 regions of China; 368 Han Chinese and 98 Uigur controls, and screened for the 235delC mutation. The coding exon of the GJB2 gene was polymerase chain reaction amplified, followed by restriction enzyme digestion with ApaI and analysis by agarose gel.

RESULTS

Overall, 488 patients (16.3%) were determined to carry at least one 235delC mutant allele, with 233 (7.8%) homozygotes and 255 (8.5%) heterozygotes. Therefore, within the subpopulations examined, the frequency varies from 0% to 14.7% for 235delC homozygotes and from 1.7% to 16.1% for heterozygotes. On the basis of this survey of the patient cohort as stated, Chinese patients with nonsyndromic hearing impairment appear to have a relatively higher 235delC frequency than that of other Asian populations.

CONCLUSION

These results demonstrate that an easy and fast genetic testing method for this well-known GJB2 gene mutation can be made available for at least 2 million Chinese patients and family members with nonsyndromic hearing impairment. By screening for the common GJB2 235delC mutation, the molecular cause in as high as 15% of patients with nonsyndromic hearing impairment in certain regions of China can be identified. In addition, patients who are negative for the 235delC mutation would be candidates for further mutational analysis of GJB2 or other deafness-related genes.

A novel hearing-loss-related mutation occurring in the GJB2 basal promoter

Mutations in the GJB2 gene are a major cause of non-syndromic recessive hearing loss in many countries. In a significant fraction of patients, only monoallelic GJB2 mutations known to be either recessive or of unclear pathogenicity are identified. This paper reports a novel GJB2 mutation, -3438C-->T, found in the basal promoter of the gene, in trans with V84M, in a patient with profound hearing impairment. This novel mutation can abolish the basal promoter activity of GJB2. These results highlight the importance of extending the mutational screening to regions outside the coding region of GJB2.

Short-term effects of intravitreal bevacizumab for subfoveal choroidal neovascularization in pathologic myopia

PURPOSE

To determine short-term effects of intravitreal bevacizumab for subfoveal choroidal neovascularization (CNV) in pathologic myopia.

METHODS

In this prospective interventional case series, patients were treated with 2.5 mg of intravitreal bevacizumab and followed for 3 months. Best-corrected visual acuity (BCVA), optical coherence tomography (OCT), and fluorescein angiography (FA) were recorded. Indications for retreatment were active leaking CNV shown by FA and presence of subretinal fluid by OCT in combination with visual disturbances.

RESULTS

Fourteen patients were included, with a mean age of 53.86 +/- 16.26 years (range 29-85). Mean spherical equivalent was -13.87 +/- 3.68 diopters (-7.25 to -20.50). Minimum follow-up was 3 months. There were no adverse events. The mean initial visual acuity was 20/200 improving to 20/100 at 2 weeks, 20/80 at 4 weeks, and 20/60 at 8 and 12 weeks (P=0.007; P=0.001; P=0.005; P=0.001, respectively). Initial foveal thickness improved from 385.43 microm +/- 125.83 microm to 257.64 +/- 76.6 microm and 194.54 +/- 54.35 microm after the first and third month, respectively (P=0.001).

CONCLUSIONS

Initial treatment results of patients with CNV due to pathologic myopia did not reveal any short-term safety concerns. Intravitreal bevacizumab resulted in a significant decrease in foveal thickness and improvement in visual acuity. These favorable initial results support further larger and long-term studies.