Nonsyndromic Hearing Loss and Deafness, DFNA3

Clinical Diagnosis

Nonsyndromic hearing loss and deafness, DFNA3, is suspected in individuals with the following:

• Pre- or postlingual, mild to profound, progressive sensorineural hearing impairment [Denoyelle et al 2002]
  
  Note: (1) Hearing is measured in decibels (dB). The threshold or 0 dB mark for each frequency refers to the level at which normal young adults perceive a tone burst 50% of the time. Hearing is considered normal if an individual's thresholds are within 15 dB of normal thresholds. (2) Severity of hearing loss is graded as mild (26-40 dB), moderate (41-55 dB), moderately severe (56-70 dB), severe (71-90dB), or profound (>90dB). The frequency of hearing loss is designated as low (<500Hz), middle (501-2000Hz), or high (>2000Hz) (see Hereditary Hearing Loss and Deafness Overview).

• No related systemic findings identified by medical history and physical examination

• A family history of nonsyndromic hearing loss consistent with autosomal dominant inheritance

Molecular Genetic Testing

GeneReviews designates a molecular genetic test as clinically available only if the test is listed in the GeneTests Laboratory Directory by either a US CLIA-licensed laboratory or a non-US clinical laboratory. GeneTests does not verify laboratory-submitted information or warrant any aspect of a laboratory's licensure or performance. Clinicians must communicate directly with the laboratories to verify information.—ED.

Gene. GJB2, which encodes connexin 26, and GJB6, which encodes connexin 30, are the only two genes known to be associated with deafness at the DFNA3 locus.

Clinical testing

• Sequence analysis
  
  GJB2. Sequence analysis of GJB2 identifies 100% of mutations, including p.Trp44Cys, p.Trp44Ser, p.Pro58Ala, p.Arg75Gln, p.Arg75Trp, p.Arg143Gln, p.Met163Leu, p.Asp179Asn, p.Arg184Gln, and p.Cys202Phe, the ten mutations reported to segregate in persons with DFNA3 [Denoyelle et al 1998, Morlé et al 2000, Hamelmann et al 2001, Janecke et al 2001, Löffler et al 2001, Marziano et al 2003, Primignani et al 2003, Feldmann et al 2005, Piazza et al 2005, Primignani et al 2007, Matos et al 2008].
  
  GJB6. A mutation in the GJB6 gene, p.Thr5Met, has been reported in one family with DFNA3 [Grifa et al 1999].

Table 1 summarizes molecular genetic testing for this condition.

Table 1. Molecular Genetic Testing Used in Nonsyndromic Hearing Loss and Deafness, DFNA3

Percent of All DFNA3	Gene Symbol	Test Method	Mutations Detected	Mutation Detection Frequency by Gene and by Test Method	Test Availability
>90%	GJB2	Sequence analysis	Sequence variants	100%	Clinical
<10%	GJB6	Sequence analysis	Sequence variants	100% 1	Clinical

1. Reported in a single Italian family by Grifa et al [1999]

Interpretation of test results. For issues to consider in interpretation of sequence analysis results, click here.

Testing Strategy

Establishing the diagnosis in a proband. For individuals suspected of having DFNA3:

• Auditory tests should be followed by a thorough physical examination to exclude distinctive features, skin disease, eye disease, and any other phenotypes that can segregate with syndromic forms of hearing loss [Hilgert et al 2009].

• The first step in the genetic diagnosis of DFNA3 is sequence analysis of GJB2 exon 2.

• If no deafness-causing mutations are identified, GJB6 should be sequenced.
  
  Note: In families segregating autosomal dominant nonsyndromic deafness, routine sequence analysis of GJB6 is not justified.

Predictive testing for at-risk asymptomatic family members requires prior identification of the deafness-causing mutation in the family.

Prenatal diagnosis and preimplantation genetic diagnosis (PGD) for at-risk pregnancies require prior identification of the deafness-causing mutation in the family.

Genetically Related (Allelic) Disorders

Other phenotypes associated with mutations in GJB2 and GJB6 include the following:

GJB2

• DFNB1, an autosomal recessive (or possibly digenic) condition of (generally) moderate-to-severe sensorineural impairment

• Palmoplantar keratoderma with deafness, characterized by diffuse hyperkeratosis of the hands and feet [Richard et al 1998, Heathcote et al 2000, Feldmann et al 2005, de Zwart-Storm et al 2008]

• Keratitis-ichthyosis-deafness (KID) syndrome, an ectodermal dysplasia characterized by vascularizing keratitis, progressive erythrokeratoderma, and profound sensorineural hearing loss as well as scarring alopecia and predisposition to squamous cell carcinoma [Richard et al 2002, van Geel et al 2002, van Steensel et al 2002]. KID syndrome is caused by heterozygous mutations in GJB2.

• Hystrix-like ichthyosis-deafness (HID) syndrome, an autosomal dominantly inherited keratinizing disorder characterized by sensorineural hearing loss and hyperkeratosis of the skin. Shortly after birth, erythroderma develops, with spiky and cobblestone-like hyperkeratosis of the entire skin surface appearing by age one year. Severe palmoplantar keratoderma and scarring alopecia occur in some. HID syndrome is considered to differ from KID syndrome in: (1) the extent and time of occurrence of skin symptoms; (2) the severity of keratitis; and (3) electron microscopic features. KID syndrome and HID syndrome are caused by the same mutation in GJB2 [van Geel et al 2002].

• Vohwinkel syndrome, an autosomal dominant condition classified as a "mutilating" diffuse keratoderma because circumferential hyperkeratosis of the digits can lead to autoamputation (termed “pseudoainhum”). Mild-to-moderate sensorineural hearing loss is often associated with the disease [Maestrini et al 1999].

• Bart-Pumphrey syndrome (BPS), an autosomal dominant disorder characterized by palmoplantar keratoderma, knuckle pads, leukonychia, and sensorineural hearing loss. The clinical features partially overlap with Vohwinkel syndrome and KID syndrome. BPS is caused by heterozygous mutations in GJB2 [Richard et al 2004].
  
  Note: The p.Met34Thr mutation in GJB2 described in a family with palmoplantar keratoderma and autosomal dominant sensorineural deafness [Kelsell et al 1997] is not a cause of dominant hearing loss [Cucci et al 2000]. This same DNA variant has been identified in normal hearing persons [Denoyelle et al 1998, Kelley et al 1998, Feldmann et al 2004], and a screen of 128 grandparents or heads of individual families not known to be related and included in CEPH (Centre d'Etude du Polymorphisme Humain) identified three individuals (2.3%) with the mutation [unpublished data].

With the mutations of GJB2 in which the epidermal disease and hearing loss cosegregate, the severity of the skin disease phenotype is highly variable, suggesting that other factors modify gene expression [Kelsell et al 2001, Feldmann et al 2005]. It is important to clinically assess each patient with autosomal dominant hearing loss for any syndromic features which may have been overlooked in affected relatives.

GJB6

• Clouston syndrome, an autosomal dominant condition characterized by hidrotic ectodermal dysplasia, alopecia, and palmoplantar hyperkeratosis [Smith et al 2002]

Natural History

Nonsyndromic hearing loss and deafness, DFNA3, is characterized by childhood-onset, progressive, moderate-to-severe high-frequency sensorineural hearing impairment. The audioprofile may vary significantly, even among family members. Individuals with DFNA3 have no other associated medical findings.

The ten missense mutations of GJB2 (p.Trp44Cys, p.Trp44Ser, p.Pro58Ala, p.Arg75Gln, p.Arg75Trp, p.Arg143Gln, p.Met163Leu, p.Asp179Asn, p.Arg184Gln, and p.Cys202Phe) that cause deafness at the DFNA3 locus are associated with at least two different audioprofiles based on age of onset.

The majority of DFNA3-causing mutations cause prelingual hearing loss (p.Trp44Cys, p.Pro58Ala, p.Arg75Gln, p.Arg75Trp, and p.Arg143Gln).

• The p.Trp44Cys audioprofile is characterized by a bilaterally symmetrical sensorineural loss that varies from mild to profound with earlier onset loss at high frequencies progressively affecting all frequencies.

• Hearing loss related to the p.Pro58Ala mutation is progressive, ranging from mild to severe.

• The hearing loss associated with the p.Arg75Gln and p.Arg75Trp mutations is usually greater (mean p.Arg75Gln threshold 105 dbHL for both ears).

• Individuals with the p.Arg143Gln mutation also show a progressive profound high frequency hearing loss [Janecke et al 2001, Löffler et al 2001, Tekin et al 2001, Denoyelle et al 2002, Feldmann et al 2005, Primignani et al 2007].

In contrast, deafness related to the p.Asp179Asn and the p.Cys202Phe mutations is post-lingual.

• Age of onset for hearing loss in individuals with the p.Asp179Asn mutation ranges from the first to the third decade. The audioprofile indicates a mild to moderate hearing loss, particularly at high frequencies.

• Hearing loss in individuals with the p.Cys202Phe mutation is usually not detected until the second decade. Initially, the loss preferentially affects the high frequencies but progresses to affect the middle frequencies by middle age [Morlé et al 2000, Denoyelle et al 2002, Primignani et al 2003].

Audioprofiles for two of the reported mutations are not available (p.Trp44Ser, p.Arg184Gln) and the age of onset of hearing loss was not reported for a third mutation (p.Met163Leu). The p.Met163Leu mutation causes a mild to moderate high frequency hearing loss [Hamelmann et al 2001, Marziano et al 2003, Matos et al 2008].

The p.Thr5Met mutation in GJB6 has only been reported in one family. In general, the audioprofile of this family is characterized by middle to high frequency hearing loss. The degree of hearing loss is progressive and variable, ranging from mild to profound. The age of onset of hearing loss was not reported [Grifa et al 1999].

Tests of vestibular function and computed tomography of the temporal bones in persons segregating these mutations have been normal [Denoyelle et al 2002].

Genotype-Phenotype Correlations

See Natural History.

Penetrance

The pathogenicity of the p.Arg75Trp mutation has been questioned, as it has been reported in one of 77 Egyptian controls whose hearing status was not reported [Richard et al 1998]. However, subsequent case reports, animal models, and functional studies strongly argue for the pathogenicity of this mutation [Janecke et al 2001, Kudo et al 2003, Maeda et al 2005, Mani et al 2009].

Anticipation

Genetic anticipation has not been observed with DFNA3.

Nomenclature

The different gene loci for nonsyndromic deafness are designated DFN (for DeaFNess).

Loci are named based on mode of inheritance:

• DFNA: Autosomal dominant

• DFNB: Autosomal recessive

• DFN: X-linked

The number following the above designations reflects the order of gene mapping and/or discovery.

Prevalence

The relative prevalence of DFNA3 as a cause of autosomal dominant nonsyndromic hearing loss is not known, but it is extremely rare. To date, 11 DFNA3 mutations have been described worldwide. The majority of these mutations are described only in single families or simplex cases (i.e., a single occurrence in a family) [Denoyelle et al 2002, Hilgert et al 2009].

Prevalence for different mutations varies by population [Abe et al 2000, Hamelmann et al 2001, Liu et al 2002, Löffler et al 2001, Xiao & Xie 2004].

Evaluations Following Initial Diagnosis

To establish the extent of involvement in an individual diagnosed with nonsyndromic hearing loss and deafness, DFNA3, a complete assessment of auditory acuity using age-appropriate tests including ABR testing, auditory steady-state response (ASSR) testing, and/or pure tone audiometry is recommended.

Treatment of Manifestations

The following are indicated:

• Fitting with appropriate hearing aids

• Enrollment in an appropriate educational program for the hearing impaired

• Consideration of cochlear implantation, a promising habilitation option for persons with profound deafness [Connell et al 2007]

• Recognition that unlike with many clinical conditions, management and treatment of mild-to-profound deafness fall largely within the purview of the social welfare and educational systems rather than the medical care system [Smith et al 2005]

Prevention of Secondary Complications

Early diagnosis, habilitation with hearing aids or cochlear implantation, and educational programming will diminish the likelihood of long-term speech or educational delay.

Surveillance

The following are appropriate:

• Semiannual examination by a physician who is familiar with hereditary hearing impairment

• Repeat audiometry to confirm stability of hearing loss

Testing of Relatives at Risk

Molecular genetic testing is recommended for at-risk relatives of individuals with a known DFNA3-causing mutation. Individuals with known pathogenic mutations should be followed semiannually by a physician who is familiar with hereditary hearing impairment.

Recommendations for the evaluation of at-risk family members when molecular genetic testing is unavailable include pure tone audiometry to assess auditory acuity and review of medical history and physical examination to rule out other systemic findings.

See Genetic Counseling for issues related to testing of at-risk relatives for genetic counseling purposes.

Therapies Under Investigation

In mice deafened by expression of the p.Arg75Trp allelic variant of GJB2, RNA interference can prevent the development of hearing loss [Maeda et al 2005].

Search ClinicalTrials.gov for access to information on clinical studies for a wide range of diseases and conditions. Note: There may not be human trials for this condition.

Other

Genetics clinics are a source of information for individuals and families regarding the natural history, treatment, mode of inheritance, and genetic risks to other family members as well as information about available consumer-oriented resources. See the GeneTests Clinic Directory.

Support groups have been established for individuals and families to provide information, support, and contact with other affected individuals. The Resources section may include disease-specific and/or umbrella support organizations.

Mode of Inheritance

Nonsyndromic hearing loss and deafness, DFNA3, is inherited in an autosomal dominant manner.

Risk to Family Members

Parents of a proband

• Most individuals diagnosed as having DFNA3 have a deaf parent; the family history is rarely negative.

• A proband with DFNA3 may have the condition as the result of a de novo gene mutation. The proportion of cases caused by de novo mutations is very small.

• Recommendations for the evaluation of parents of a proband with an apparent de novo mutation include assessment of auditory acuity using ABR emission testing and pure tone audiometry and medical history and physical examination to rule out other systemic findings.

Sibs of a proband

• The risk to sibs depends on the genetic status of the proband's parents.

• If one of the proband's parents has a deafness-causing allele, each sib has a 50% chance of inheriting the mutant allele.

• When the parents are clinically unaffected, the risk to the sibs of a proband appears to be low.

• If a mutation causing DFNA3 cannot be detected in the DNA extracted from leukocytes of either parent, two possible explanations are germline mosaicism in a parent or a de novo mutation in the proband. Although no instances of germline mosaicism have been reported, it remains a possibility.

Offspring of a proband. Offspring of an affected individual have a 50% chance of inheriting the mutant allele.

Other family members of a proband. The risk to other family members depends on the status of the proband's parents. If a parent is found to be deaf, his or her family members are at risk.

Related Genetic Counseling Issues

Establishing in infancy or early childhood whether a child at risk has inherited the altered GJB2 or GJB6 gene should be considered so that appropriate and early support and management can be provided to the child and the family. Molecular genetic testing for the mutation can only be considered if a deafness-causing mutation has been identified in an affected family member. Additional points to consider are the following:

• Communication with individuals who are deaf requires the services of a skilled interpreter.

• Deaf persons may view deafness as a distinguishing characteristic and not as a handicap, impairment, or medical condition requiring a "treatment" or "cure," or to be "prevented." In fact, having a deaf child may be preferred over having a child with normal hearing.

• Many deaf people are interested in obtaining information about the cause of their own deafness including information on medical, educational, and social services rather than information about prevention, reproduction, or family planning. As in all genetic counseling, it is important for the counselor to identify, acknowledge, and respect the individual's/family's questions, concerns, and fears.

• The use of certain terms is preferred: probability or chance vs risk; deaf and hard-of-hearing vs hearing impaired. Terms such as "affected," "abnormal," and "disease causing" should be avoided.

Family planning

• The optimal time for determination of genetic risk and discussion of the availability of prenatal testing is before pregnancy.

• It is appropriate to offer genetic counseling (including discussion of potential risks to offspring and reproductive options) to young adults who are deaf.

Considerations in families with an apparent de novo mutation. When neither parent of a proband with an autosomal dominant condition has the mutation or clinical evidence of the condition, it is likely that the proband has a de novo mutation. However, possible non-medical explanations including alternate paternity or maternity (e.g., with assisted reproduction) or undisclosed adoption could also be explored.

DNA banking is the storage of DNA (typically extracted from white blood cells) for possible future use. Because it is likely that testing methodology and our understanding of genes, mutations, and diseases will improve in the future, consideration should be given to banking DNA of deaf individuals. DNA banking is particularly relevant when the sensitivity of currently available testing is less than 100%. See for a list of laboratories offering DNA banking.

Prenatal Testing

Prenatal testing for pregnancies at 50% risk is possible by analysis of DNA extracted from fetal cells obtained by amniocentesis usually performed at approximately 15-18 weeks' gestation or chorionic villus sampling (CVS) at approximately ten to 12 weeks' gestation. The mutation in GJB2 or GJB6 causing DFNA3 in the family must be identified before prenatal testing can be performed.

Note: Gestational age is expressed as menstrual weeks calculated either from the first day of the last normal menstrual period or by ultrasound measurements.

Requests for prenatal testing for conditions such as DFNA3 are not common. Differences in perspective may exist among medical professionals and within families regarding the use of prenatal testing, particularly if the testing is being considered for the purpose of pregnancy termination rather than early diagnosis. Although most centers would consider decisions about prenatal testing to be the choice of the parents, discussion of these issues is appropriate.

Preimplantation genetic diagnosis (PGD) may be available for families in which the deafness-causing mutation has been identified. For laboratories offering PGD, see .

GJB2

Normal allelic variants. Most connexin genes have a common architecture, with the entire coding region contained in a single large exon separated from the 5'-untranslated region by an intron of variable size. The coding sequence of GJB2 (exon 2) is 681 base pairs (including the stop codon) and is translated into a 226-amino acid protein, connexin 26 (Cx26). Numerous benign alleles of GJB2 have been reported and are listed on the Connexin-Deafness Home Page.

Pathologic allelic variants. There are ten known DFNA3-causing mutations in GJB2 (see Table 2). The majority of these mutations have been shown to segregate in families; however, the p.Arg75Gln and p.Arg75Trp mutations of GJB2 have also been identified as de novo mutations in simplex cases (i.e., a single occurrence in a family). These two mutations are implicated in both autosomal dominant nonsyndromic hearing loss and syndromic hearing loss associated with skin disorders [Janecke et al 2001, Feldmann et al 2005].

Normal gene product. Connexin 26 is a beta-2 gap junction protein. Gap junctions are highly specialized organelles consisting of clustered channels that permit direct intercellular exchange of ions and molecules through central aqueous pores. Postulated roles include the rapid propagation of electrical signals and synchronization of activity in excitable tissues and the exchange of metabolites and signal molecules in non-excitable tissues [Evans & Martin 2002].

Each connexin protein contains two extracellular (E1-E2), four transmembrane (M1-M4), and three cytoplasmic domains (N-terminus, C-terminus, and a cytoplasmic loop located between M2 and M3). Each extracellular domain contains three cysteine residues joined between the E1 and E2 loops by at least one disulfide bond [Kovacs et al 2007, Yeager & Harris 2007]. The presumed importance of these six cysteines can be inferred from Cx32 experiments in which any Cys mutation completely blocks the development of gap-junction conductances between Xenopus oocyte pairs. The third transmembrane domain (M3) is amphipathic and lines the putative wall of the intercellular channel [Kovacs et al 2007, Yeager & Harris 2007], which is created by oligomerization of six connexins to form a hexameric structure called a connexon. Two connexons, one from each cell, join in the extracellular gap to complete the cell-to-cell pathway. If the connexons contributed by each cell are of identical composition, the channel is homotypic; if each connexon is formed by a different composition of connexins, it is termed heterotypic. Most connexins are phosphoproteins and undergo post-transcriptional modifications [Moreno 2005, Locke et al 2006]. Cx26 forms functional combinations with itself, Cx30, Cx31, Cx32, Cx46, and Cx50 [Cottrell & Burt 2005, Liu et al 2009].

Abnormal gene product. Gap junction channels are permeable to ions and small metabolites with relative molecular masses up to approximately 1.2 kd [Harris & Bevans 2001]. Differences in ionic selectivity and gating mechanisms among gap junctions reflect the existence of over 20 different connexin isoforms in humans.

The abnormal gene product in DFNA3 causes deafness via a dominant negative mechanism of action. Half of the DFNA3-causing mutations in GJB2 have been functionally tested for dominant negative effects in recombinant expression systems (p.Trp44Cys, p.Trp44Ser, p.Arg75Trp, p.Arg75Gln, and p.Met163Leu). The ability to prevent formation of functional gap junction channels was first demonstrated with the p.Arg75Trp mutation in a Xenopus oocyte model system [Richard et al 1998, Mani et al 2009]. The p.Trp44Cys, p.Trp44Ser, and p.Arg75Gln mutations have been shown to prevent functional channel formation in vitro [Bruzzone et al 2001, Marziano et al 2003, Piazza et al 2005]. In addition to dominant negative inhibition of wild-type Cx26, the p.Trp44Ser and p.Arg75Trp mutations show a transdominant negative effect on wild-type Cx30 channel formation. The p.Met163Leu mutation shows a dominant negative effect on appropriate protein trafficking and cell viability [Matos et al 2008].

GJB6

Normal allelic variants. The majority of gap junction genes have two exons; a few have only one exon, and one, GJB6, has three exons, of which only the third is coding. The translated protein, connexin 30 (Cx30), is 261 amino acids long.

Pathologic allelic variants. The only known DFNA3-causing pathologic variant of GBJ6 is the p.Thr5Met mutation [Grifa et al 1999] (see Table 3).

Normal gene product. Connexin 30 is a beta-6 gap junction protein. It shares an architecture that is common to all connexins (see GJB2, Normal gene product).

Abnormal gene product. Like the abnormal gene products of GJB2 in DFNA3, the p.Thr5Met mutation of GJB6 acts via a dominant negative mechanism to inhibit activity of wild-type Cx30 gap junction channels [Grifa et al 1999].

Literature Cited

Published Statements and Policies Regarding Genetic Testing

Suggested Reading

Acknowledgments

This work was originally supported in part by research grants 1RO1 DC02842 (RJHS), HG00457 (VCS), P50HG00835 (VCS), and Belgian National Fonds voor Wetenschappelijk Onderzoek (GVC).

Author History

Daryl A Scott, MD, PhD; University of Iowa (1998-2001)
Abraham M Sheffield (2009-present)
Val C Sheffield, MD, PhD; University of Iowa (1998-2001)
Richard JH Smith, MD (1998-present)
Guy Van Camp, PhD (1998-present)

Revision History

• 30 April 2009 (me) Comprehensive update posted live

• 29 December 2005 (me) Comprehensive update posted to live Web site

• 15 July 2004 (rjs) Revision: use of an interpreter

• 27 October 2003 (me) Comprehensive update posted to live Web site

• 24 April 2001 (me) Comprehensive update posted to live Web site

• 28 September 1998 (pb) Review posted to live Web site

• 4 April 1998 (rjs) Original submission