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

Cxs and Panx- hemichannels in peripheral and central chemosensing in mammals

Connexins (Cxs) and Pannexins (Panx) form hemichannels at the plasma membrane of animals. Despite their low open probability under physiological conditions, these hemichannels release signaling molecules (i.e., ATP, Glutamate, PGE₂) to the extracellular space, thus subserving several important physiological processes. Oxygen and CO₂ sensing are fundamental to the normal functioning of vertebrate organisms. Fluctuations in blood PO₂, PCO₂ and pH are sensed at the carotid bifurcations of adult mammals by glomus cells of the carotid bodies. Likewise, changes in pH and/or PCO₂ of cerebrospinal fluid are sensed by central chemoreceptors, a group of specialized neurones distributed in the ventrolateral medulla (VLM), raphe nuclei, and some other brainstem areas. After many years of research, the molecular mechanisms involved in chemosensing process are not completely understood. This manuscript will review data regarding relationships between chemosensitive cells and the expression of channels formed by Cxs and Panx, with special emphasis on hemichannels.

Mutation detection in GJB2 gene among Malays with non-syndromic hearing loss

OBJECTIVES

To identify the mutations in the GJB2 gene and to determine its association with non-syndromic hearing loss in Malays.

METHODS

A comparative cross sectional study was conducted on a group of children from the deaf schools and the normal schools. A total of 91 buccal cell samples of non-syndromic hearing loss and 91 normal hearing children were taken. Polymerase chain reaction was used to amplify the coding region of GJB2 gene. The PCR product of GJB2 coding region was preceded with screening for mutations using denaturing high performance liquid chromatography (dHPLC) and mutations detected were confirmed by DNA sequencing.

RESULTS

Twelve sequence variations including mutations and polymorphisms were found in 32 patients and 37 control subjects. The variations were G4D, V27I, E114G, T123N, V37I and R127H in both groups, W24X, R32H, 257_259 del CGC and M34L in patients only and I203T and V153I in control subjects only. There were no association between homozygous (P=0.368) or heterozygous (P=0.164) GJB2 gene and non-syndromic hearing loss.

CONCLUSIONS

The types of GJB2 gene mutation were different and vary in Malay non-syndromic hearing loss as compared to the other races. Furthermore, the mutation did not associate with hearing loss in the population. Other related genes are believed to be involved and need to be sought in this group of patients.

Anxiety of the mothers with referred baby during Universal Newborn Hearing Screening

OBJECTIVE

To investigate the anxiety among mothers whom their babies have failed test results in the first stage of Universal Neonatal Hearing Screening Program.

PATIENTS AND METHODS

A cross-sectional study was carried out on mothers whom their baby have positive test results in the first stage of Universal Neonatal Hearing Screening Program. Face to face interview was conducted to obtain data on sociodemographic profiles, knowledge about hearing loss and past medical history. Symptoms experienced by the mothers due to positive hearing test results and level of anxiety were measured by using the Malay translation Beck Anxiety Inventory questionnaire. These mothers were then given an appointment to come for the second screening six weeks after the first screening. The same questionnaire was given to them before the start of the second screening. SPSS version 11.5 was used for data entry and analysis. Wilcoxon signed Rank Test was used to compare the level of anxiety between the first and second screening.

RESULTS

From a total of 78 mothers who were participated during the first screening, 50 of them have completed the study at the second screening (response rate=64%). Fifty-two percent of them knew about the hearing screening before hand. Ninety-six percent of the mothers became alert about their child response towards sounds after they knew that their child had failed the first hearing screening. During the first screening, 74% of the mothers felt mild anxiety which was decreased to 68% before the mothers undergone the second screening. Moderate anxiety was felt by 10% of the mothers during both the first and second screening. There were 8% of the mothers having severe anxiety during the first screening but have reduced to half (4%) before the mothers undergone the second screening. The anxiety level was significantly less before the second screening with the median score of 5 (IQR: 13.0) compared to after the first screening (8, IQR=14.25); p=0.001.

CONCLUSIONS

There are considerable portion of the mothers of false-positive test result during Universal Neonatal Hearing Screening Program experienced unacceptable anxiety. This group of mothers needs to be identified and given a necessary help.

Prevalence of the c.35delG and p.W24X mutations in the GJB2 gene in patients with nonsyndromic hearing loss from North-West Romania

OBJECTIVE

In Central and South-Eastern European countries, the most frequent mutation types responsible for congenital nonsyndromic sensorineural hearing loss (NSHL) are c.35delG and p.W24X (15-55.8% and 2.5-4.3%, respectively). The aim of the study was to determine for the first time in Romania the prevalence of c.35delG and p.W24X mutations in patients with NSHL.

MATERIAL

75 unrelated children with NSHL from Transylvania (North-West Romania).

METHODS

a. Audiological examination (otoscopy, tympanogram, acoustic otoemission and tonal audiogram or auditory evoked potentials); b. detection of the c.35delG (semi-nested-PCR, RFLP and ARMS-PCR analysis) and p.W24X (ARMS-PCR analysis) mutations.

RESULTS

Audiological examination allowed the diagnosis of hearing loss of various degrees: moderate in 8 patients (10.7%), severe in 14 cases (18.7%), profound in 53 patients (70.6%). The number of reported mutation cases as against the number of alleles indicates a 33.3% frequency rate for c.35delG mutation and respectively 5.3% for p.W24X mutation. All 22 patients with 35delG/c.35delG genotype (19 patients), c.35delG/p.W24X genotype (2 patients) or p.W24X/p.W24X genotype (1 patient) presented profound/severe hearing loss.

CONCLUSION

Our study confirms that the frequency rate of the two mutations analyzed in patients with NSHL from North-West Romania is comparable to that seen in other Central and South-Eastern European countries. The homozygote or compound heterozygote states represent a major risk factor for profound or severe deafness. Audiological screening in newborns and genetic testing in confirmed congenital hypoacusis cases are compulsory for early therapeutic intervention (hearing prosthesis or cochlear implant) and genetic counselling.