Autosomal Recessive Nonsyndromic Hearing Impairment: an Overview

WITHDRAWN. Universal neonatal hearing screening versus selective screening as part of the management of childhood deafness

BACKGROUND

The principal factors that decide how deafness affects a child's development are the degree of hearing impairment and the age at which it is diagnosed. A number of factors are thought to increase the risk of hearing impairment: low birth weight, prematurity, perinatal hypoxia and jaundice, among others. The high incidence of deafness in children without risk factors and the introduction of simple new screening tests of high sensitivity and specificity have led many prestigious bodies to recommend universal early detection programmes for deafness rather than screening targeted only at high-risk groups.

OBJECTIVES

To compare the long-term effectiveness of a universal neonatal screening and early treatment programme for hearing impairment with: a) screening and treatment only of high-risk neonates and b) opportunistic screening and treatment.

SEARCH STRATEGY

Databases searched included MEDLINE (1966 to 2006), EMBASE (1974 to 2006), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 2, 2006) and registers of health technology assessment agencies as well as registers of clinical guidelines. The date of the last search was June 2006.

SELECTION CRITERIA

Randomised controlled trials comparing universal neonatal screening with either high-risk screening or opportunistic screening for hearing impairment.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened the search results to identify suitable trials.

MAIN RESULTS

No studies were identified which fulfilled the inclusion criteria.

AUTHORS' CONCLUSIONS

The long-term effectiveness of universal newborn hearing screening programmes has not been established to date. There is a need for controlled trials and before and after studies to address this issue further.

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

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<or=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<or=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.

Universal neonatal hearing screening versus selective screening as part of the management of childhood deafness

BACKGROUND

The principal factors that decide how deafness affects a child's development are the degree of hearing impairment and the age at which it is diagnosed. A number of factors are thought to increase the risk of hearing impairment: low birth weight, prematurity, perinatal hypoxia and jaundice, among others. The high incidence of deafness in children without risk factors and the introduction of simple new screening tests of high sensitivity and specificity has led many prestigious bodies to recommend universal early detection programmes for deafness rather than screening targeted only at high-risk groups.

OBJECTIVES

To compare the long-term effectiveness of a universal neonatal screening and early treatment programme for hearing impairment with: a) screening and treatment only of high-risk neonates and b) opportunistic screening and treatment.

SEARCH STRATEGY

Databases searched were MEDLINE (1966 to 2003), EMBASE (1974 to 2003), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 1, 2004) and registers of health technology assessment agencies as well as registers of clinical guidelines.

SELECTION CRITERIA

Randomised controlled trials comparing universal neonatal screening with either high-risk screening or opportunistic screening for hearing impairment.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened the search results to identify suitable trials.

MAIN RESULTS

No studies were identified which fulfilled the inclusion criteria.

AUTHORS' CONCLUSIONS

The long-term effectiveness of universal newborn hearing screening programmes has not been established to date. There is a need for controlled trials and before and after studies to address this issue further.