Statement of the American College of Medical Genetics on Universal Newborn Hearing Screening

"My Plate is Full": Reasons for Declining a Genetic Evaluation of Hearing Loss

The aim of this study was to obtain patient and parent perspectives on genetic evaluation of hearing loss, in order to identify motivators, expectations, and barriers. Three focus groups were conducted following a semi-structured discussion guide, led by an independent moderator. Participants were hearing parents of children with permanent hearing loss or deaf adults. Qualitative content analysis was used to develop a codebook and identify major themes and subthemes. Participant views were compared to national guidelines. The 28 participants comprised 23 parents representing 21 unique families and 5 deaf adults. 13/21 families and 0/5 adults reported comorbidities, 4/21 families and 3/5 adults had a positive family history, and 12/21 families versus 0/5 adults had utilized genetics services. A common theme among adults and parents was a curiosity as to the cause of hearing loss. Parents were motivated to detect comorbidities and optimize care for hearing loss. Some parents felt overwhelmed by the hearing loss and unprepared to pursue early genetic evaluation as recommended in guidelines. Several reported positive experiences following genetics consultation, while others reported unease and unmet expectations. Notably, both parents and adults expressed ambivalence regarding the desire for genetic knowledge. Financial concerns and difficulties obtaining a referral were cited as extrinsic barriers. For parents of children with hearing loss, both the presence of comorbidities and a positive family history were drivers of genetics consultation and/or genetic testing. We identified educational opportunities for both patients and providers that would improve informed decision-making and increase access to genetic services. Consideration of the patient/family perspective and their decision-making processes, along with flexibility in the approach to genetics evaluation and its timing, will optimize both the development and implementation of guidelines.

New directions in cytogenetic and molecular testing of the neonate

The development of new diagnostic, and hence therapeutic possibilities, has brought the realization that genetic disease is now an integral part of medical practice. Advances in cytogenetic and molecular testing have drastically improved the ability to diagnose with certainty many previously unrecognized conditions. However, this advance in technology does not come without new questions. New tests are not always the most cost effective ones, some have significant diagnostic limitations, and others raise valid ethical issues surrounding the testing of minors. A working understanding of new advances in genetic diagnosis as well as their inherent limitations is crucial for the contemporary practitioner.

Audiometric evaluation of carriers of the connexin 26 mutation 35delG

Mutation in a gap junction protein gene (GJB2 also named connexin 26) is a major cause of autosomal recessive congenital deafness, which is responsible for about 80% of the cases in Mediterranean families, but actually little is known about the influence of GJB2 mutations on the hearing of obligate carriers. We examined GJB2 35delG mutation carrier individuals to test the possible presence and incidence of audiometric abnormalities among carriers of 35delG mutations. Tonal audiometric analysis was performed on a 35delG mutation carrier group (H) and on a non-carrier control group (N). Audiometric evaluations in the control group showed the presence of thresholds within normal limits at all frequencies, while carriers of 35delG mutations presented a decrease of hearing principally at 6,000 and 8,000 Hz. The difference at 6,000 and 8,000 Hz between groups H and N is statistically significant.

Spectrum and frequencies of mutations in the GJB2 (Cx26) gene among 156 Czech patients with pre-lingual deafness

Mutations in the gene gap junction beta 2 (GJB2), the gene for the connexin 26, are the most common cause of pre-lingual deafness worldwide. The mutation 35delG within GJB2 is prevalent in Europe. To date, there are no data about GJB2 mutation spectrum and frequencies from the Czech population. We investigated and report here the spectrum and frequencies of mutations in the GJB2 gene among 156 unrelated, congenital deafness Czech patients. Allele-specific polymerase chain reaction, together with fluorescent fragment analysis, were used for the detection of the 35delG mutation. The entire coding region of the GJB2 was directly sequenced in all patients who were not homozygous for the 35delG. No pathogenic mutation was detected in 51.9% of patients. At least one pathogenic mutation was found in 48.1% of patients, and both pathogenic mutations were detected in 37.8% of patients. Single mutations in a heterozygous state were detected in 10.3% of patients. The mutation 35delG accounts for 82.8% of detected disease mutations, Trp24stop accounts for 9.7% of pathogenic alleles and was found in patients with gypsy heritage. Mutation 313del14 accounts for 3.7% of pathogenic alleles. The frequency of 35delG heterozygotes in the Czech Republic is 1 : 29.6. Testing for only the three most common mutations would detect over 96% of all pathogenic alleles in the Czech Republic.

The implications of genetic testing for deafness

Using modern biotechnology, it is increasingly common that genes can be identified and characterized, their protein products can be understood and tests to identify changes in these genes that lead to disease can be developed. Genetic tests are rapidly being introduced into clinical practice. Although there are many clinical benefits of genetic testing for a variety of medical conditions, there are also important practical and ethical concerns about the applications of genetic testing. The recent introduction of genetic tests for common forms of hereditary deafness (see also Rehm, 2003, in this issue) also promises many clinical benefits. Many of the same ethical concerns for genetic testing in general, also apply to genetic testing for deafness, with the added concerns brought about by the existence of the linguistic and cultural differences of the Deaf community. Sensitive genetic counseling performed by skilled geneticists is an important part of the genetic testing process to ensure that families and individuals can make informed choices regarding the use of genetic testing.

Early childhood hearing loss: clinical and molecular genetics. An educational slide set of the American College of Medical Genetics

An educational slide set entitled "Early Childhood Hearing Loss: Clinical and Molecular Genetics" is offered by the American College of Medical Genetics (ACMG). The slide set is produced in Microsoft PowerPoint 2002. It is extensively illustrated and supported with teaching tools, explanations of each slide and figure, links to Internet resources, and a bibliography. The slide set is expected to be used as a resource for self-directed learning and in support of medical genetics teaching activities. The slide set is available through the ACMG (http://www.acmg.net) for $20, plus applicable tax and shipping. It is the first in a series of educational slide sets to be developed by the ACMG.

Prevalence of GJB2 mutations in prelingual deafness in the Greek population

OBJECTIVE

Mutations in the gene encoding the gap junction protein connexin 26 (GJB2) have been shown as a major contributor to prelingual, sensorineural, nonsyndromic, recessive deafness. One specific mutation, 35delG, has accounted for the majority of the mutations detected in the GJB2 gene in Caucasian populations. The aim of our study was to determine the prevalence and spectrum of GJB2 mutations in prelingual deafness in the Greek population.

METHODS

In a collaboration with the major referral centers for childhood deafness in Greece, patients were examined by an extensive questionnaire to exclude syndromic forms and environmental causes of deafness and by allele-specific polymerase chain reaction (PCR) for the detection of the 35delG mutation. Patients heterozygous for the 35delG mutation were further analyzed by direct genomic sequencing of the coding region of the GJB2 gene.

RESULTS

The 35delG mutation was found in 42.2% of the chromosomes in 45 familial cases of prelingual, nonsyndromic deafness (18 homozygotes and 2 heterozygotes) and in 30.6% of the chromosomes in 165 sporadic cases (45 homozygotes and 11 heterozygotes). Direct genomic sequencing in heterozygous patients revealed the L90P (2 alleles), W24X (2 alleles), R184P (2 alleles), and 291insA (1 allele) mutations.

CONCLUSION

Mutations in the GJB2 gene are responsible for about one third of prelingual, sensorineural, nonsyndromic deafness in the Greek population, and allele-specific PCR is an easy screening method for the common 35delG mutation.

Effectiveness of sequencing connexin 26 (GJB2) in cases of familial or sporadic childhood deafness referred for molecular diagnostic testing

PURPOSE

Hearing loss is a common congenital disorder that is frequently associated with mutations in the GJB2 gene encoding the connexin 26 protein (Cx26). We sought to evaluate the effectiveness of direct DNA sequencing for detection of Cx26 mutations as a clinical diagnostic test.

METHODS

We designed a clinical assay using a three-step polymerase chain reaction (PCR)-based DNA sequencing strategy to detect all possible mutations in the open reading frame and flanking sequences of Cx26. The results of the first 324 cases of childhood deafness referred for diagnostic testing were analyzed.

RESULTS

A total of 127 of the 324 (39.2%) cases had at least one mutant Cx26 allele (36.1% of sporadic cases, 70% of familial cases). Of these 127 case, 57 (44.8%) were homozygotes or compound heterozygotes. Thirty-four different mutations were identified, including 10 novel mutations, 6 of which (T8M, K15T, R32L, M93I, N206S, and 511-512insAACG) may be pathogenic. We also provide new evidence on the pathogenicity or nonpathogenicity of 12 previously reported mutations, and clarify the confusing nomenclature of the 313-326del14 mutation.

CONCLUSION

A simple and rigorous method for efficient PCR-based sequence analysis of Cx26 is a sensitive clinical assay for evaluating deaf children. Its widespread use is likely to identify additional pathogenic mutations and lead to a better understanding of the clinical significance of previously identified mutations.

GJB2 (connexin 26) variants and nonsyndromic sensorineural hearing loss: a HuGE review

Despite the enormous heterogeneity of genetic hearing loss, variants in one locus, Gap Junction Beta 2 or GJB2 (connexin 26), account for up to 50% of cases of nonsyndromic sensorineural hearing loss in some populations. This article reviews genetic epidemiology studies of the alleles of GJB2, prevalence rates, genotype-phenotype relations, contribution to the incidence of hearing loss, and other issues related to the clinical validity of genetic testing for GJB2. This review focuses primarily on three alleles: 167 Delta T, 35 Delta G, and 235 Delta C. These alleles are recessive for nonsyndromic prelingual sensorineural hearing loss, and the evidence suggests complete penetrance but variable expressivity.

Genetics Evaluation Guidelines for the Etiologic Diagnosis of Congenital Hearing Loss. Genetic Evaluation of Congenital Hearing Loss Expert Panel. ACMG statement

The advent of hearing screening in newborns in many states has led to an increase in the use of genetic testing and related genetic services in the follow-up of infants with hearing loss. A significant proportion of those with congenital hearing loss have genetic etiologies underlying their hearing loss. To ensure that those identified with congenital hearing loss receive the genetic services appropriate to their conditions, the Maternal and Child Health Bureau of the Health Resources and Services Administration funded the American College of Medical Genetics to convene an expert panel to develop guidelines for the genetic evaluation of congenital hearing loss. After a brief overview of the current knowledge of hearing loss, newborn screening, and newborn hearing screening, we provide an overview of genetic services and a guideline that describes how best to ensure that patients receive appropriate genetic services. The significant contribution of genetic factors to these conditions combined with the rapid evolution of knowledge about the genetics of these conditions overlaid with the inherently multidisciplinary nature of genetic services provides an example of a condition for which a well-integrated multidisciplinary approach to care is clearly needed.