The use of buccal smears for a non-invasive screening of the 35delG mutation of the Connexin-26 gene in hearing impaired young children

Summary Objectives Recent advances in genetic research indicate that about 50% of congenital deaf patients have a genetic background, with mutations in the Connexin-26 gene being the most frequent one. Screening methods for the genetic cause of deafness have so far mostly been based on the use of peripheral whole blood as DNA source. The use of buccal smears for the genetic screening of deaf patients presents an interesting alternative to drawing blood, especially in young children. In order to validate this method, we compared results from buccal smears from very young deaf children (age ≤ 3 years) and deaf patients older than 3 years with the results from blood samples deriving from the same patients. Methods The detection of the 35delG mutation in the Connexin-26 gene was chosen to demonstrate the method's feasibility. Blood and buccal smears were collected for genetic analysis from 29 very young deaf children (Group 1: age ≤ 3 years) and 31 deaf patients older than 3 years (Group 2) during their clinical pre-evaluation for cochlear implantation. Genomic DNA was isolated from blood as well as from buccal smears. Yield of both sources was determined by photometric evaluation of the isolated DNA concentration. Genomic DNA isolated from blood and buccal smears was then submitted to PCR-mediated site-directed mutagenesis followed by BS1 YI restriction and electrophoresis. The results for 35delG detection in DNA originating from blood were compared to those of buccal smears. Results Quantitative DNA analysis showed that both sources provided adequate amounts of DNA for PCR. No significant difference was found between Group 1 and Group 2 considering either the DNA amount isolated from blood or from buccal smears. In all 60 patients, DNA isolated from blood revealed the same results concerning the presence of the 35delG mutation as DNA originating from buccal smears. Conclusions This study demonstrates that buccal smears are an adequate, reliable source of genomic DNA providing material for genetic tests that can especially help to avoid drawing blood from very young children for the genetic screening of deafness.