Hearing impairment is the partial or complete inability to hear that leads to compromise the development of normal language skills. Among all the sensory impairments in humans, hearing impairment is the most common.
It is estimated that at least 50% of the cases are due to genetic factors. Hereditary hearing loss may be syndromic or non-syndromic; about 30% of deafness cases are syndromic, while 70% is non-syndromic. It is estimated that the prevalence of profound bilateral hearing loss is 1.6 per 1000 in Pakistan and 70% of hearing loss arises in consanguineous families. The main pattern of inheritance of deafness in Pakistani population is autosomal recessive and to date more than 145 loci and 26 genes have been identified for non-syndromic recessive deafness.
More than 400 disorders associated with hearing loss shows extreme genetic heterogeneity and complexity of the mammalian inner ear. As more genes are identified, the elucidation of the function of the proteins that these genes encode contributes greatly to the understanding of cochlear mechanisms and their role in disease causation.
The gene involved, GJB2, encodes the connexin26 molecule. Connexin26 is a component of gap junctions, the links that allow small molecules to pass from one cell to the next, and this protein is found in several places in the body, including the epithelial supporting cells surrounding the sensory ear cells of the cochlea.The sensory ear cells of the cochlea allow potassium ions to pass through their upper surface during normal reception of sound, and these potassium ions must be recycled through the base of the ear cells and the supporting cells and fibrocytes back into the high-potassium endolymph that bathes the tops of the ear cells.
The aim of this study was Linkage analysis for DFNB1 locus involved in causing hereditary deafness in families from Khyber Pukhtunkhwa. A total of 10 families were enrolled from different areas of Khyber Pukhtunkhwa province. I have studied 8 families of these 10 (i.e.) family no. 2, 3, 4, 5, 6, 8, 9 and 10. The families have at least three affected individuals. All the families showed recessive mode of inheritance. For linkage analysis studies for DFNB1 locus, three STR markers D13S175, D13S292, and D13S787 were genotyped using Polyacrylamide gel electrophoresis (PAGE) and haplotypes were constructed to determined, linkage with DFNB1 locus. From a total of 8 families, a single family was linked to DFNB1 locus. The DFNB1 locus is the first non-syndromic deafness locus mapped to chromosome 13q12.