Abstract:
Introduction: Hearing impairment is one of the most common widespread birth
defects and one of every 1000 new born has bilateral permanent Sensorineural
Hearing Loss (SNHL). About 50% of SNHL involves genetic factors and 46 genes
have been identified as causally related to nonsyndromic SNHL. In spite of this
large genetic heterogeneity, mutations in GJB2 and GJB6 genes are primarily
responsible for most of the genetic hearing loss. A free radical is an unstable
cluster of molecules can cause errors in genetic “messages” by altering DNA. This
can, among other things, lead to a reduced blood supply to organs such as the inner
ear and brain, there by damaging hearing. Our bodies produce enzymes known as
antioxidants, such as Superoxide Dismutase (SOD) and catalase to counteract the
damage.
Objectives: To study to investigate the genetic cause of deafness by genetic
screening of the GJB2 genes and enzyme and catalase in deaf patients.
Methodology: Patients with sensorineural congenital HI were selected after
obtaining their consents. Clinical samples were tested using PCR/RFLP for
35delG & 167delT mutations. PCR was used to amplify two regions of the exon 2
of connexin26 and PCR products were analyzed using Bsl I and Pst I. Blood level
of SOD and catalase was estimated by spectrophotometric analysis.
Results: 87.8% had normal genotype for the studied mutations, 4.88% were
compound heterozygotes, 7.32% homozygotic for the 35delG mutation, 9.76%
heterozygotic for 35delG/GJB2. The 167delT mutation was not detected in any of
the deaf individuals.
Discussion: Our data confirmed the presence of the 35delG mutation in the GJB2
gene in cases of non-syndromic bilateral moderate to profound sensorineural
hearing loss in West Bengal. For the 167delT mutation the allele frequency was
zero for the familial and sporadic groups. These findings underline the importance
of a genetic diagnosis that may clarify the etiology and provide early treatment for
children. Genetic counseling for their family members will help in early detection
and treatment.
