Variable hearing impairment in a DFNB2 family with a novel MYO7A missense mutation

Myosin VIIA mutations have been associated with non-syndromic hearing loss (DFNB2; DFNA11) and Usher syndrome type 1B (USH1B). We report clinical and genetic analyses of a consanguineous Iranian family segregating autosomal recessive non-syndromic hearing loss (ARNSHL). The hearing impairment was mapped to the DFNB2 locus using Affymetrix 50K GeneChips; direct sequencing of the MYO7A gene was completed. The Iranian family (L-1419) was shown to segregate a novel homozygous missense mutation (c.1184G>A) that results in a p.R395H amino acid substitution in the motor domain of the myosin VIIA protein. As one affected family member had significantly less severe hearing loss, we used a candidate approach to search for a genetic modifier. This novel MYO7A mutation is the first reported to cause DFNB2 in the Iranian population and this DFNB2 family is the first to be associated with a potential modifier. The absence of vestibular and retinal defects, and less severe low frequency hearing loss, is consistent with the phenotype of a recently reported Pakistani DFNB2 family. Thus, we conclude this family has non-syndromic hearing loss (DFNB2) rather than USH1B, providing further evidence that these two diseases represent discrete disorders.

Mutation profile of the CDH23 gene in 56 probands with Usher syndrome type I

Mutations in the human gene encoding cadherin23 (CDH23) cause Usher syndrome type 1D (USH1D) and nonsyndromic hearing loss. Individuals with Usher syndrome type I have profound congenital deafness, vestibular areflexia and usually begin to exhibit signs of RP in early adolescence. In the present study, we carried out the mutation analysis in all 69 exons of the CDH23 gene in 56 Usher type 1 probands already screened for mutations in MYO7A. A total of 18 of 56 subjects (32.1%) were observed to have one or two CDH23 variants that are presumed to be pathologic. Twenty one different pathologic genome variants were observed of which 15 were novel. Out of a total of 112 alleles, 31 (27.7%) were considered pathologic. Based on our results it is estimated that about 20% of patients with Usher syndrome type I have CDH23 mutations.

Genetic counseling in Usher syndrome: linkage and mutational analysis of 10 Colombian families

Usher Syndrome (US), an autosomal recessive disease, is characterized by retinitis pigmentosa (RP), vestibular dysfunction, and congenital sensorineural deafness. There are three recognized clinical types of the disorder. In order to improve genetic counseling for affected families, we conducted linkage analysis and DNA sequencing in 10 Colombian families with confirmed diagnosis of US (4 type I and 6 type II). Seventy-five percent of the US1 families showed linkage to locus USH1B, while the remaining 25% showed linkage to loci USH1B and USH1C. Among families showing linkage to USH1B we found two different mutations in the MYO7A gene: IVS42-26insTTGAG in exon 43 (heterozygous state) and R634X (CGA-TGA) in exon 16 (homozygous state). All six US2 families showed linkage to locus USH2A. Of them, 4 had c.2299delG mutation (1 homozygote state and 3 heterozygous); in the remaining 2 we did not identify any pathologic DNA variant. USH2A individuals with a 2299delG mutation presented a typical and homogeneous retinal phenotype with bilateral severe hearing loss, except for one individual with a heterozygous 2299delG mutation, whose hearing loss was asymmetric, but more profound than in the other cases. The study of these families adds to the genotype-phenotype characterization of the different types and subtypes of US and facilitates genetic counseling in these families. We would like to emphasize the need to perform DNA studies as a prerequisite for genetic counseling in affected families.

OTOF mutations revealed by genetic analysis of hearing loss families including a potential temperature sensitive auditory neuropathy allele

INTRODUCTION

The majority of hearing loss in children can be accounted for by genetic causes. Non-syndromic hearing loss accounts for 80% of genetic hearing loss in children, with mutations in DFNB1/GJB2 being by far the most common cause. Among the second tier genetic causes of hearing loss in children are mutations in the DFNB9/OTOF gene.

METHODS

In total, 65 recessive non-syndromic hearing loss families were screened by genotyping for association with the DFNB9/OTOF gene. Families with genotypes consistent with linkage or uninformative for linkage to this gene region were further screened for mutations in the 48 known coding exons of otoferlin.

RESULTS

Eight OTOF pathological variants were discovered in six families. Of these, Q829X was found in two families. We also noted 23 other coding variant, believed to have no pathology. A previously published missense allele I515T was found in the heterozygous state in an individual who was observed to be temperature sensitive for the auditory neuropathy phenotype.

CONCLUSIONS

Mutations in OTOF cause both profound hearing loss and a type of hearing loss where otoacoustic emissions are spared called auditory neuropathy.

[From gene to disease; genetic causes of hearing loss and visual impairment sometimes accompanied by vestibular problems (Usher syndrome)]

Usher syndrome is an autosomal recessively inherited disease, characterised by sensorineural hearing loss, tapetoretinal degeneration and in some cases vestibular problems. Based on the clinical heterogeneity, the disease can be classified into three clinical types (I, II and III), which have their own genetic subtypes (Usher 1A-Usher IG, Usher 2A-Usher 2C and Usher 3). The majority of the Usher type I cases are caused by mutations in the MYO7A gene (Usher 1B) while mutations in the USH2A gene (Usher 2A) are the cause of most cases of type II. Usher syndrome type III, caused by mutations in the USH3 gene, is frequently seen only in Finland.

CDH23 mutation and phenotype heterogeneity: a profile of 107 diverse families with Usher syndrome and nonsyndromic deafness

Usher syndrome type I is characterized by congenital hearing loss, retinitis pigmentosa (RP), and variable vestibular areflexia. Usher syndrome type ID, one of seven Usher syndrome type I genetic localizations, have been mapped to a chromosomal interval that overlaps with a nonsyndromic-deafness localization, DFNB12. Mutations in CDH23, a gene that encodes a putative cell-adhesion protein with multiple cadherin-like domains, are responsible for both Usher syndrome and DFNB12 nonsyndromic deafness. Specific CDH23 mutational defects have been identified that differentiate these two phenotypes. Only missense mutations of CDH23 have been observed in families with nonsyndromic deafness, whereas nonsense, frameshift, splice-site, and missense mutations have been identified in families with Usher syndrome. In the present study, a panel of 69 probands with Usher syndrome and 38 probands with recessive nonsyndromic deafness were screened for the presence of mutations in the entire coding region of CDH23, by heteroduplex, single-strand conformation polymorphism, and direct sequence analyses. A total of 36 different CDH23 mutations were detected in 45 families; 33 of these mutations were novel, including 18 missense, 3 nonsense, 5 splicing defects, 5 microdeletions, and 2 insertions. A total of seven mutations were common to more than one family. Numerous exonic and intronic polymorphisms also were detected. Results of ophthalmologic examinations of the patients with nonsyndromic deafness have found asymptomatic RP-like manifestations, indicating that missense mutations may have a subtle effect in the retina. Furthermore, patients with mutations in CDH23 display a wide range of hearing loss and RP phenotypes, differing in severity, age at onset, type, and the presence or absence of vestibular areflexia.

Clinical and genetic features of nonsyndromic autosomal dominant sensorineural hearing loss: KCNQ4 is a gene responsible in Japanese

Sixteen Japanese nonsyndromic autosomal dominant sensorineural hearing loss (ADSNHL) families were investigated clinically as well as genetically. Most families showed postlingual hearing loss. Although the severity of their hearing loss varied, most patients showed mild-moderate sensorineural hearing loss of a progressive nature. Mutation analysis was performed for the MYO7A, KCNQ4, and GJB3 genes, which are known to be responsible for autosomal dominant sensorineural hearing loss. The present study reports that a mutation in KCNQ4, a member of a large family of potassium channel genes, was responsible for ADSNHL in one Japanese family.

Genetic features of hearing loss associated with ear anomalies: PDS and EYA1 mutation analysis

Mutation analysis of the PDS gene and the EYA1 gene, which are reported to be responsible for hearing loss associated with ear anomalies, was performed in 24 deaf patients with various middle and inner ear anomalies. The present study was done to clarify the spectrum of middle and inner ear malformations covered by these two genes. PDS mutations were found only in patients with enlarged vestibular aqueducts and EYA1 mutations were detected only in patients with ear pits and cervical fistulae, indicating that these two genes are associated with particular forms of middle and inner ear malformation. The genetic approach provides a strong tool for the diagnosis of hearing loss associated with ear anomalies.

Connexin 26 gene (GJB2) mutation modulates the severity of hearing loss associated with the 1555A-->G mitochondrial mutation

We report a high prevalence of GJB2 heterozygous mutations in patients bearing the 1555A-->G mitochondrial mutation, and describe a family in which potential interaction between GJB2 and a mitochondrial gene appears to be the cause of hearing impairment. Patients who are heterozygotes for the GJB2 mutant allele show hearing loss more severe than that seen in sibs lacking a mutant GJB2 allele, suggesting that heterozygous GJB2 mutations may synergistically cause hearing loss when in the presence of a 1555A-->G mutation. The present findings indicate that GJB2 mutations may sometimes be an aggravating factor, in addition to aminoglycoside antibiotics, in the phenotypic expression of the non-syndromic hearing loss associated with the 1555A-->G mitochondrial mutation.

A common ancestral origin of the frequent and widespread 2299delG USH2A mutation

Usher syndrome type IIa is an autosomal recessive disorder characterized by mild-to-severe hearing loss and progressive visual loss due to retinitis pigmentosa. The mutation that most commonly causes Usher syndrome type IIa is a 1-bp deletion, described as "2299delG," in the USH2A gene. The mutation has been identified in several patients from northern and southern Europe and from North America, and it has been found in single patients from South America, South Africa, and China. Various studies have reported a range of frequencies (.16-.44) among patients with Usher syndrome, depending on the geographic origin of the patients. The 2299delG mutation may be the one that most frequently causes retinitis pigmentosa in humans. Given the high frequencies and the wide geographic distribution of the mutation, it was of interest to determine whether the mutation resulted from an ancestral mutational event or represented a mutational hotspot in the USH2A gene. Haplotype analysis was performed on DNA samples from 116 unrelated patients with Usher syndrome type IIa; the patients were from 14 countries and represented 148 2299delG alleles. On the basis of six single-nucleotide polymorphisms within the USH2A gene, 12 core haplotypes were observed in a panel of normal chromosomes. However, in our analysis, only one core haplotype was found to be associated with the 2299delG mutation. The data indicate that the widespread geographic distribution of the 2299delG mutation is the result of an ancestral mutation that has spread throughout Europe and into the New World as a result of migration.

Spectrum of mutations in USH2A in British patients with Usher syndrome type II

Usher syndrome (USH) is a combination of a progressive pigmentary retinopathy, indistinguishable from retinitis pigmentosa, and some degree of sensorineural hearing loss. USH can be subdivided in Usher type I (USHI), type II (USHII) and type III (USHIII), all of which are inherited as autosomal recessive traits. The three subtypes are genetically heterogeneous, with six loci so far identified for USHI, three for USHII and only one for USHIII. Mutations in a novel gene, USH2A, encoding the protein usherin, have recently been shown to be associated with USHII. The gene encodes a protein with partial sequence homology to both laminin epidermal growth factor and fibronectin motifs. We analysed 35 British and one Pakistani Usher type II families with at least one affected member, for sequence changes in the 20 translated exons of the USH2A gene, using heteroduplex analysis and sequencing. Probable disease-causing mutations in USH2A were identified in 15 of 36 (41.7%) Usher II families. The most frequently encountered mutation (11/15 families or 11/18 mutated alleles) was del2299G in exon 13, resulting in a frameshift and premature stop codon. Other mutations include insertions and point mutations, of which two are previously unreported. Five different polymorphisms were also detected. Our results indicate that mutations in this gene are responsible for disease in a large proportion of British Usher type II patients. Moreover, if screening for mutations in USH2A is considered, it is sensible to screen for the del2299G mutation first.

A new clinical classification for Usher's syndrome based on a new subtype of Usher's syndrome type I

OBJECTIVES

Usher's syndrome is an autosomal recessive disorder characterized by sensorineural hearing loss and progressive visual loss secondary to retinitis pigmentosa. Usher's syndrome is both clinically and genetically heterogeneous. Three clinical types are known today.

METHODS

We conducted a study on 74 patients with Usher's syndrome, performing complete audiological and neurotological examinations.

RESULTS

Twenty-six patients had total profound hearing loss and retinitis pigmentosa (Usher's syndrome type I), and 48 patients had moderate to severe sensorineural hearing loss and retinitis pigmentosa (Usher's syndrome type II). We identified 9 of the 26 Usher's syndrome patients with profound hearing loss who showed a normal response to bithermal vestibular testing.

CONCLUSIONS

The combination of profound hearing loss and normal response to bithermal vestibular testing has not been previously described in Usher's syndrome. Therefore we describe a new subtype of Usher's syndrome type I and suggest a modified clinical classification for Usher's syndrome.

Genetic heterogeneity of Usher syndrome

Progress towards the understanding of the molecular basis of US has been substantial. Nine different loci have been found to be responsible and two have had the specific gene identified. This information is expected to lay the foundation for the eventual development of new treatment strategies. Usher syndrome is the combined loss of both of humans most important two senses and a better understanding of the genes involved should not only help the families with US but will also provide much needed basic information about the hearing and visual systems.

Autosomal-dominant, prelingual, nonprogressive sensorineural hearing loss: localization of the gene (DFNA8) to chromosome 11q by linkage in an Austrian family

A four-generation family suffering from an autosomal-dominant, congenital, nonprogressive, nonsyndromic hearing loss was found in a rural region of Austria. The hearing loss was moderate to severe, a pure tone audiogram showing a U-shaped form with maximum loss at 2, 000 Hz. An initial genome search led to a lod score of 3.01 with markers on chromosome 15. This locus was registered as DFNA8 in the HUGO data base. Further sampling of the family, however, yielded data that reduced the maximal lod score with chromosome 15 markers to 1.81. The genome search was restarted using an ABITM genotyper, which eventually detected several positive two-point lod scores with markers from the long arm of chromosome 11. The highest value was 3. 6, which was seen with the marker D11S934. Haplotype analysis excluded the gene from the chromosomal region proximal from D11S898 and distal to D11S1309. These results place the gene in the region of the hearing loss gene DFNA12. Recent evidence suggests that the somewhat different phenotypes found in these two families are due to two different mutations in the human alpha-tectorine gene (Verhoeven et al., 1998).

Identification of novel USH2A mutations: implications for the structure of USH2A protein

Usher syndrome type II is an autosomal recessive disorder, characterised by stable hearing impairment from childhood and progressive retinitis pigmentosa from the late teens. Mutations in the USH2A gene, located on 1q41, were recently shown to be responsible for Usher syndrome type IIa. We have investigated the molecular pathology of Usher type II by screening the USH2A gene for mutations in 31 unrelated patients from Denmark and Norway. Besides the frequent 2299delG mutation, which accounted for 44% of the disease alleles, a heterogeneous spectrum of mutations was identified. Sixteen new, putative disease-causing mutations were detected, of which 12 were private and four were shared by unrelated patients. The disease-causing mutations were scattered throughout the gene and included six nonsense and seven missense mutations, two deletions and one small insertion. In addition, six non-pathogenic polymorphisms were identified. All missense mutations resulted in major amino acid side-chain alterations. Four missense mutations affected the N-terminal part of USH2A, whereas three missense mutations affected the laminin-type epidermal growth factor-like (LE) domain. The structural consequences of the mutations affecting the LE domain are discussed in relation to the three-dimensional structure of a LE-module of the mouse laminin gamma1 chain.

Identification of three novel mutations in human EYA1 protein associated with branchio-oto-renal syndrome

The Branchio-oto-renal (BOR) syndrome is an autosomal dominant disorder characterized by branchial clefts, preauricular sinuses, hearing loss, and renal anomalies. Recent studies have shown that mutations in EYA1 are associated with BOR. However, the underlying molecular mechanisms by which mutations in the EYA1 gene cause BOR syndrome are unknown. We have investigated 12 unrelated Caucasian families for mutations by heteroduplex analysis and direct sequencing of products from the polymerase chain reaction. In this study, we identified two novel frameshift deletions and a single base substitution that introduces a stop codon mutation in the C-terminal region of the EYA1 gene. No obvious relationships were observed between the nature of the mutations and the variable clinical features associated with BOR syndrome.

Genomewide search and genetic localization of a second gene associated with autosomal dominant branchio-oto-renal syndrome: clinical and genetic implications

Branchio-oto-renal (BOR) syndrome is characterized by ear malformations, cervical fistulas, hearing loss, and renal anomalies. It is an autosomal dominant disorder with variable clinical manifestations. The most common features of BOR syndrome are branchial, hearing, and renal anomalies. However, many affected subjects have been observed with branchial-cleft anomalies and hearing loss but without renal anomalies, a condition called "branchio-otic" (BO) syndrome. It is logical to question whether the BOR and BO syndromes are allelic or whether they represent distinct genetic entities. We identified a very large extended family whose members had branchial and hearing anomalies associated with commissural lip pits that segregated in an autosomal dominant fashion. Using a genomewide search strategy, we identified genetic linkage, with a maximum LOD score of 4.81 at recombination fraction 0, between the BO phenotype and polymorphic marker D1S2757 in the genetic region of chromosome 1q31. This is the first report of linkage for a second gene associated with BOR syndrome. The findings have important clinical implications and will provide insight into the genetic basis of BOR syndrome.

Genetic heterogeneity of Usher syndrome type II: localisation to chromosome 5q

Usher syndrome is a group of autosomal recessive disorders that includes retinitis pigmentosa (RP) with hearing loss. Usher syndrome type II is defined as moderate to severe hearing loss with RP. The USH2A gene at 1q41 has been isolated and characterised. In 1993, a large Usher II family affected with a mild form of RP was found to be unlinked to 1q41 markers. Subsequent linkage studies of families in our Usher series identified several type II families unlinked to USH2A and USH3 on 3q25. After a second unlinked family with many affected members and a mild retinal phenotype was discovered, a genome search using these two large families showed another Usher II locus on 5q (two point lod = 3.1 at D5S484). To date, we have identified nine unrelated 5q linked families (maximum combined multipoint lod = 5.86) as well as three Usher II families that show no significant linkage to any known Usher loci. Haplotype analysis of 5q markers indicates that the new locus is flanked by D5S428 and D5S433. Review of ophthalmological data suggests that RP symptoms are milder in 5q linked families; the RP is often not diagnosed until patients near their third decade. Enamel hypoplasia and severe, very early onset RP were observed in two of the three unlinked families; dental anomalies have not been previously described as a feature of Usher type II.

Three novel mutations and twelve polymorphisms identified in the USH2A gene in Israeli USH2 families

The Usher syndromes are autosomal recessive hereditary disorders characterized by hearing impairment and progressive visual loss due to Retinitis Pigmentosa (RP). Moderate to severe sensorineural hearing loss and progressive RP characterizes Usher syndrome type IIa (USH2A), which maps to the long arm of chromosome 1q41. Recently, three deletions carried by USH2 patients, which were found in a novel gene isolated from the critical 1q41 region, defined this gene as responsible for USH2A. The USH2A gene is predicted to encode a 1546 amino acid protein which possesses domains that are observed in basal lamina and extracellular matrix proteins and in cell adhesion molecules. Affected individuals and additional members from eleven USH2 Israeli families of diverse ethnic origin were screened for the presence of changes in all 20 coding exons of the USH2A gene. Three novel mutations (239-242insCGTA, R334W, T1515M) were identified in three families of Jewish Moroccan and Jewish Iranian origins. Twelve polymorphisms were found in the families, four of which are novel. None of the known USH2 mutations were identified in the families studied in this work. Hum Mutat 15:388, 2000.

Connexin 26: required for normal auditory function

A single base deletion mutation, 35delG, in the gene (GJB2/DFNB1)(OMIM 121011/220290) encoding the gap junction protein, connexin 26 is the most important single cause of genetic hearing loss in European and American populations. It is the cause of one of the most common human genetic disorders with a frequency similar to cystic fibrosis. Mutations in this connexin are associated with skin disorders.

Erratum: analysis of DNA elements that modulate myosin VIIa expression in humans

Usher syndromeIb (USH1B), an autosomal recessive disorder caused by mutations in myosin VIIa (MYO7A), is characterized by congenital profound hearing loss, vestibular abnormalities and retinitis pigmentosa. Promoter elements in the 5 kb upstream of the translation start were identified using adult retinal pigment epithelium cells (ARPE-19) as a model system. A 160 bp minimal promoter within the first intron was active in ARPE-19 cells, but not in HeLa cells that do not express MYO7A. A 100 bp sequence, 5' of the first exon, and repeated with 90% homology within the first intron, appeared to modulate expression in both cell lines. Segments containing these elements were screened by heteroduplex analysis. No heteroduplexes were detected in the minimal promoter, suggesting that this sequence is conserved. A -2568 A>T transversion in the 5' 100 bp repeat, eliminating a CCAAT element, was found only in USH1B patients. However, in all 5 families, -2568 A>T was in cis with the same missense mutation in the myosin VIIa tail (Arg1240Gln), and 4 of the 5 families were Dutch. These observations suggest either 1) linkage disequilibrium or 2)that a combination of a promoter mutation with a less active myosin VIIa protein results in USH1B.

Prevalent connexin 26 gene (GJB2) mutations in Japanese

The gene responsible for DNFB1 and DFNA3, connexin 26 (GJB2), was recently identified and more than 20 disease causing mutations have been reported so far. This paper presents mutation analysis for GJB2 in Japanese non-syndromic hearing loss patients compatible with recessive inheritance. It was confirmed that GJB2 mutations are an important cause of hearing loss in this population, with three mutations, 235delC, Y136X, and R143W, especially frequent. Of these three mutations, 235delC was most prevalent at 73%. Surprisingly, the 35delG mutation, which is the most common GJB2 mutation in white subjects, was not found in the present study. Our data indicated that specific combinations of GJB2 mutation exist in different populations.

Human connexin 30 (GJB6), a candidate gene for nonsyndromic hearing loss: molecular cloning, tissue-specific expression, and assignment to chromosome 13q12

Mutations in connexin 26 are responsible for approximately 20% of genetic hearing loss and 10% of all childhood hearing loss. However, only about 75% of the mutations predicted to be in Cx26 are actually observed. While this may be due to mutations in noncoding regulatory regions, an alternative hypothesis is that some cases may be due to mutations in another gene immediately adjacent to Cx26. Another gap junction gene, connexin 30 (HGMW-approved symbol GJB6), is found to lie on the same PAC clone that hybridizes to chromosome 13q12. Human connexin 26 and connexin 30 are expressed in the same cells of the cochlea. Cx26 and Cx30 share 77% identity in amino acid sequence but Cx30 has an additional 37 amino acids at its C-terminus. These considerations led us to hypothesize that mutations in Cx30 might also be responsible for hearing loss. Eight-eight recessive nonsyndromic hearing loss families from both American and Japanese populations were screened for mutations. In addition, 23 dominant hearing loss families and 6 singleton families presumed to be recessive were tested. No significant mutation has been found in the dominant or recessive families.

Analysis of DNA elements that modulate myosin VIIA expression in humans

Usher syndromeIb (USH1B), an autosomal recessive disorder caused by mutations in myosin VIIa (MYO7A), is characterized by congenital profound hearing loss, vestibular abnormalities and retinitis pigmentosa. Promoter elements in the 5 kb upstream of the translation start were identified using adult retinal pigment epithelium cells (ARPE-19) as a model system. A 160 bp minimal promoter within the first intron was active in ARPE-19 cells, but not in HeLa cells that do not express MYO7A. A 100 bp sequence, 5' of the first exon, and repeated with 90% homology within the first intron, appeared to modulate expression in both cell lines. Segments containing these elements were screened by heteroduplex analysis. No heteroduplexes were detected in the minimal promoter, suggesting that this sequence is conserved. A -2568 A>T transversion in the 5' 100 bp repeat, eliminating a CCAAT element, was found only in USH1B patients. However, in all 5 families, -2568 A>T was in cis with the same missense mutation in the myosin VIIa tail (Arg1240Gln), and 4 of the 5 families were Dutch. These observations suggest either 1) linkage disequilibrium or 2)that a combination of a promoter mutation with a less active myosin VIIa protein results in USH1B.

Branchio-oto-renal syndrome: identification of novel mutations, molecular characterization, mutation distribution, and prospects for genetic testing

The branchio-oto-renal syndrome (BOR) is an autosomal dominant disorder characterized by branchial clefts, preauricular sinuses, hearing loss, and renal anomalies. The BOR gene, EYA1, on chromosome 8q13 has recently been cloned and mutations have been identified. In this study, we have analyzed the sites of mutations in the EYA1 gene in BOR patients to determine the spectrum of mutations. We have identified two missense mutations and have compared all the mutations reported to date in the EYA1 gene. In total, 20 mutations have been described, the majority of which are clustered in the carboxy-terminal region of the gene. The clinical features of the BOR individuals have also been compared to determine if the nature of the mutation correlates with the type and severity of the clinical symptoms. Most of the mutations arose de novo and, other than the clustering in carboxy-terminal exons 9-16, no mutation hot spots have been identified. These results provide the basis for molecular genetic testing that will help in the clinical evaluation and genetic counseling of members of BOR families.

EYA1 nonsense mutation in a Japanese branchio-oto-renal syndrome family

Advances in molecular genetics have recently revealed that mutations in the EYA1 gene are responsible for branchio-oto-renal (BOR) syndrome in European and other populations. This is the first report confirming that an EYA1 gene mutation is also disease-causing in an Asian population. We have described one Japanese BOR syndrome family showing a novel mutation in exon 7 of the EYA1 gene. There was extensive variation of clinical phenotypes within this family. When the physician is confronted with a BOR family showing a wide variation in clinical expression, molecular genetic testing helps to achieve accurate diagnosis.

Confirmation of linkage of Van der Woude syndrome to chromosome 1q32: evidence of association with STR alleles suggests possible unique origin of the disease mutation

Van der Woude syndrome (VWS) is an autosomal dominant craniofacial disorder with high penetrance and variable expression. Its clinical features are variably expressed, but include cleft lip and/or cleft palate, lip pits and hypodontia. All VWS families studied to date map the disease gene to a < 2 cM region of chromosome 1q32, with no evidence of locus heterogeneity. The aim of this study is to refine the localization of the VWS gene and to further assess possible heterogeneity. We analyzed four multiplex VWS families. All available members were clinically assessed and genotyped for 19 short tandem repeat markers on chromosome 1 in the VWS candidate gene region. We performed two-point and multipoint limit of detection (LOD) score analyses using a high penetrance autosomal dominant model. All families showed positive LOD scores without any recombination in the candidate region. The largest two-point LOD score was 5.87. Our assay method for short tandem repeat (STR) markers provided highly accurate size estimation of marker allele fragment sizes, and therefore enabled us to determine the specific alleles segregating with the VWS gene in each of our four families. We observed a striking pattern of STR allele sharing at several closely linked loci among our four Caucasian VWS families recruited at three different locations in the US. These results suggest the possibility of a unique origin for a mutation responsible for many or most cases of VWS.

Clinical studies of families with hearing loss attributable to mutations in the connexin 26 gene (GJB2/DFNB1)

OBJECTIVE

This retrospective study describes the phenotype associated with the single most common cause of genetic hearing loss. The frequency of childhood deafness is estimated at 1/500. Half of this hearing loss is genetic and approximately 80% of genetic hearing loss is nonsyndromic and inherited in an autosomal recessive manner. Approximately 50% of childhood nonsyndromic recessive hearing loss is caused by mutations in the connexin 26 (Cx26) gene (GJB2/DFNB1), making it the most common form of autosomal recessive nonsyndromic hearing loss with a carrier rate estimated to be as high as 2.8%. One mutation, 35delG, accounts for approximately 75% to 80% of mutations at this gene.

METHODS

Hearing loss was examined in 46 individuals from 24 families who were either homozygous or compound heterozygous for Cx26 mutations. A subset of these individuals were examined for vestibular function, otoacoustic emissions, auditory brainstem response, temporal bone computed tomography, electrocardiography, urinalyses, dysmorphology, and thyroid function.

RESULTS

Although all persons had hearing impairment, no consistent audiologic phenotype was observed. Hearing loss varied from mild-moderate to profound, even within the group of families homozygous for the common mutation 35delG, suggesting that other factors modify the phenotypic effects of mutations in Cx26. Furthermore, the hearing loss was observed to be progressive in a number of cases. No associations with inner ear abnormality, thyroid dysfunction, heart conduction defect, urinalyses, dysmorphic features, or retinal abnormality were noted.

CONCLUSION

Newborns with confirmed hearing loss should have Cx26 testing. Cx26 testing will help define a group in which approximately 60% will have profound or severe-profound hearing loss and require aggressive language intervention (many of these patients will be candidates for cochlear implants).

Human NDUFB9 gene: genomic organization and a possible candidate gene associated with deafness disorder mapped to chromosome 8q13

Human NADH dehydrogenase (ubiquinone) 1beta-subcomplex, 9 (NDUFB9) is a nuclear encoded mitochondrial protein with the respiratory electron transport chain. It has been physically mapped to a 1-Mb deletion at chromosome 8q13 which also contains the gene for branchio-oto-renal (BOR) syndrome. BOR syndrome is characterized by branchial and renal abnormalities with hearing impairment. Since several hereditary deafness disorders have been associated with mitochondrial mutations, NDUFB9 was considered a candidate gene for BOR syndrome. Recently, EYA1 gene has been identified in the region which underlies the BOR syndrome but majority of BOR families did not show mutations in the EYA1 gene. Here we have determined the genomic structure of the NDUFB9 gene, including the nucleotide sequence, organization and the boundaries of the four coding exons. PCR primers were designed from the adjacent intron sequences that allow amplification of the four exons that encode the complete open reading frame. To identify whether mutations in NDUFB9 are involved in causing the BOR syndrome, we screened 9 BOR families which did not show mutations in the EYA1 gene by heteroduplex analysis; however, no mutations were found.

Fluctuating sensorineural hearing loss associated with enlarged vestibular aqueduct maps to 7q31, the region containing the Pendred gene

The most common form of inner ear abnormality, enlarged vestibular aqueduct (EVA), is of particular interest because it is associated with characteristic clinical findings, including fluctuating and sometimes progressive sensorineural hearing loss and disequilibrium symptoms. Although EVA has been reported to be inherited in a recessive manner, nothing else is known about the genetic basis of this hearing loss. Here we report on the localization of the gene responsible for sensorineural hearing loss associated with EVA to chromosomal region 7q31, with maximum multipoint LOD score of 3.647. The EVA candidate gene region lies in a 1.7-cM interval between the flanking markers D7S501 and D7S2425. Interestingly, this region overlaps the region containing the gene responsible for Pendred syndrome, called PDS, which was identified recently. However, the present subjects did not fulfill the criteria for Pendred syndrome. It is hypothesized that different mutations within the PDS gene may cause different phenotypes ranging from EVA to the Mondini deformity seen in Pendred syndrome.

Non-syndromic hearing loss associated with enlarged vestibular aqueduct is caused by PDS mutations

Enlarged vestibular aqueduct (EVA), known as the most common form of inner ear abnormality, has recently been of particular genetic interest because this anomaly is inherited in a recessive manner. The locus for non-syndromic sensorineural hearing loss with EVA has been mapped to the same chromosomal region, 7q31, as the Pendred syndrome locus. In the present study, seven mutations in the PDS gene (PDS), the gene responsible for Pendred syndrome, have been found in families of non-syndromic sensorineural hearing loss with EVA. One family is homozygous, three families are compound heterozygotes, and two families are heterozygous but with no other mutation detected. The present results provide evidence that mutations in PDS cause both syndromic and non-syndromic hearing loss.

Phylogenetic analysis of mitochondrial DNA in Japanese pedigrees of sensorineural hearing loss associated with the A1555G mutation

Thirteen Japanese families (ten of which were from the northern part of Japan), with sensorineural hearing loss associated with the 1555 A to G (A1555G) mitochondrial mutation, a known cause of non-syndromic hearing loss, were phylogenetically analysed using data obtained by restriction fragment length polymorphism (RFLP) and D-loop sequencing of mitochondrial DNA (mtDNA). Various types of mtDNA polymorphism were detected by restriction enzymes and D-loop sequence. No common polymorphic pattern throughout the 13 families was found, though three families exhibited the same restriction patterns and the same sequence substitution in the D-loop. To find where each of the 13 families are situated in the phylogenetic tree, the 482-bp of D-loop sequence were compared with those of 62 normal Japanese subjects. Despite the three families mentioned above appearing to be clustered, the remaining 10 families were scattered along the phylogenetic tree. This indicates that there was no common ancestor for the 13 Japanese families bearing the A1555G mutation except three families, and that the A1555G mutation occurred sporadically and multiplied through evolution of the mtDNA in Japan. The present results showed that the common pathogenicity (hearing loss associated with the A1555G mutation) can occur sporadically in families which have different genetic backgrounds, even in the Japanese population.

Medical genetic evaluation for the etiology of hearing loss in children

The purpose of the medical genetic evaluation is to identify the etiology of the hearing loss. To do so requires a multidisciplinary team that includes the otolaryngologist, audiologist, medical geneticist, and radiologist. A number of tests and procedures are now available to assist in the search for the cause of hearing losses. The importance of sensitivity when providing genetic counseling is emphasized. Molecular genetics offers potential for continued progress in understanding the etiologies of hearing loss. Recent advances in this area are discussed.

Sensorineural hearing loss caused by mitochondrial DNA mutations: special reference to the A1555G mutation

Mutations in mitochondrial DNA, which are maternally inherited, have been thought to be one of the causes of sensorineural hearing loss. Two mitochondrial mutational sites (A1555G, A7445G) have been reported to be responsible for non-syndromic hearing impairments. The A1555G mutation causes increased susceptibility to aminoglycoside antibiotic-induced hearing loss as well as non-syndromic sensorineural hearing loss. Our wide screening study showed that there may be a great number of subjects within the Japanese population who have the A1555G mutation. Recent reports suggest that high-risk populations may exist throughout the world. The aminoglycoside-induced hearing loss associated with a mitochondrial mutation is commonly bilateral, symmetric, high frequency involved, and is sometimes associated with progressive sensorineural hearing loss.

Volumetric neuroimaging in Usher syndrome: evidence of global involvement

Usher syndrome is a group of genetic disorders consisting of congenital sensorineural hearing loss and retinitis pigmentosa of variable onset and severity depending on the genetic type. It was suggested that the psychosis of Usher syndrome might be secondary to a metabolic degeneration involving the brain more diffusely. There have been reports of focal and diffuse atrophic changes in the supratentorial brain as well as atrophy of some of the structures of the posterior fossa. We previously performed quantitative analysis of magnetic resonance imaging studies of 19 Usher syndrome patients (12 with type I and 7 with type II) looking at the cerebellum and various cerebellar components. We found atrophy of the cerebellum in both types and sparing of cerebellar vermis lobules I-V in type II Usher syndrome patients only. We now have studied another group of 19 patients (with some overlap in the patients studied from the previous report) with Usher syndrome (8 with type I, 11 with type II). We performed quantitative volumetric measurements of various brain structures compared to age- and sex-matched controls. We found a significant decrease in intracranial volume and in size of the brain and cerebellum with a trend toward an increase in the size of the subarachnoid spaces. These data suggest that the disease process in Usher syndrome involves the entire brain and is not limited to the posterior fossa or auditory and visual systems.

Mutation of a gene encoding a protein with extracellular matrix motifs in Usher syndrome type IIa

Usher syndrome type IIa (OMIM 276901), an autosomal recessive disorder characterized by moderate to severe sensorineural hearing loss and progressive retinitis pigmentosa, maps to the long arm of human chromosome 1q41 between markers AFM268ZD1 and AFM144XF2. Three biologically important mutations in Usher syndrome type IIa patients were identified in a gene (USH2A) isolated from this critical region. The USH2A gene encodes a protein with a predicted size of 171.5 kilodaltons that has laminin epidermal growth factor and fibronectin type III motifs; these motifs are most commonly observed in proteins comprising components of the basal lamina and extracellular matrixes and in cell adhesion molecules.

Isepamicin sulfate-induced sensorineural hearing loss in patients with the 1555 A-->G mitochondrial mutation

A mitochondrial mutation at nucleotide 1555 has been reported to be susceptible to aminoglycoside antibiotics as well as one of the causes of nonsyndromic sensorineural hearing loss. We herewith report 2 cases bearing the 1555 A-->G mitochondrial mutation who had hearing loss after short-term exposure to the new aminoglycoside antibiotic, isepamicin sulfate. Even when using aminoglycoside antibiotics with milder side effects, careful attention should be paid in applying them to patients with particular genetic backgrounds.

Mutations in the human alpha-tectorin gene cause autosomal dominant non-syndromic hearing impairment

The tectorial membrane is an extracellular matrix of the inner ear that contacts the stereocilia bundles of specialized sensory hair cells. Sound induces movement of these hair cells relative to the tectorial membrane, deflects the stereocilia, and leads to fluctuations in hair-cell membrane potential, transducing sound into electrical signals. Alpha-tectorin is one of the major non-collagenous components of the tectorial membrane. Recently, the gene encoding mouse alpha-tectorin (Tecta) was mapped to a region of mouse chromosome 9, which shows evolutionary conservation with human chromosome 11q (ref. 3), where linkage was found in two families, one Belgian (DFNA12; ref. 4) and the other, Austrian (DFNA8; unpublished data), with autosomal dominant non-syndromic hearing impairment. We determined the complete sequence and the intron-exon structure of the human TECTA gene. In both families, mutation analysis revealed missense mutations which replace conserved amino-acid residues within the zona pellucida domain of TECTA. These findings indicate that mutations in TECTA are responsible for hearing impairment in these families, and implicate a new type of protein in the pathogenesis of hearing impairment.

Autosomal-dominant branchio-otic (BO) syndrome is not allelic to the branchio-oto-renal (BOR) gene at 8q13

The manifestations of branchio-oto-renal syndrome (BOR), Treacher Collins syndrome, tricho-rhino-phalangeal syndrome, van der Woude syndrome, and Langer-Giedion syndrome are well-defined; these conditions represent clinically and genetically separate syndromes. Autosomal-dominant branchio-oto-renal syndrome comprises preauricular pits, branchial fistulas, hearing loss, and renal anomalies. However, several families have been described without one or more of these clinical findings. In some families, the phenotypic expression is limited to branchial anomalies, preauricular pits, and hearing loss, with no renal dysplasia (branchio-otic or BO syndrome). In other families, branchial and renal anomalies occur without hearing impairment. It is not known whether the variable clinical manifestations are due to the effect of a single gene or whether these represent different syndromes. We investigated BO syndrome in a large family to determine whether BOR and BO syndromes are allelic to each other. The genetic linkage analysis provides evidence that BO syndrome is not allelic to the BOR gene at 8q13.

Novel mutations in the connexin 26 gene (GJB2) that cause autosomal recessive (DFNB1) hearing loss

Mutations in the connexin 26 (Cx26) gene (GJB2) are associated with the type of autosomal recessive nonsyndromic neurosensory deafness known as "DFNB1." Studies indicate that DFNB1 (13q11-12) causes 20% of all childhood deafness and may have a carrier rate as high as 2. 8%. This study describes the analysis of 58 multiplex families each having at least two affected children diagnosed with autosomal recessive nonsyndromic deafness. Twenty of the 58 families were observed to have mutations in both alleles of Cx26. Thirty-three of 116 chromosomes contained a 30delG allele, for a frequency of .284. This mutation was observed in 2 of 192 control chromosomes, for an estimated gene frequency of .01+/-.007. The homozygous frequency of the 30delG allele is then estimated at .0001, or 1/10,000. Given that the frequency of all childhood hearing impairment is 1/1,000 and that half of that is genetic, the specific mutation 30delG is responsible for 10% of all childhood hearing loss and for 20% of all childhood hereditary hearing loss. Six novel mutations were also observed in the affected population. The deletions detected cause frameshifts that would severely disrupt the protein structure. Three novel missense mutations, Val84Met, Val95Met, and Ser113Pro, were observed. The missense mutation 101T-->C has been reported to be a dominant allele of DFNA3, a dominant nonsyndromic hearing loss. Data further supporting the finding that this mutation does not cause dominant hearing loss are presented. This allele was found in a recessive family segregating independently from the hearing-loss phenotype and in 3 of 192 control chromosomes. These results indicate that 101T-->C is not sufficient to cause hearing loss.

Human bZIP transcription factor gene NRL: structure, genomic sequence, and fine linkage mapping at 14q11.2 and negative mutation analysis in patients with retinal degeneration

The NRL gene encodes an evolutionarily conserved basic motif-leucine zipper transcription factor that is implicated in regulating the expression of the photoreceptor-specific gene rhodopsin. NRL is expressed in postmitotic neuronal cells and in lens during embryonic development, but exhibits a retina-specific pattern of expression in the adult. To understand regulation of NRL expression and to investigate its possible involvement in retinopathies, we have determined the complete sequence of the human NRL gene, identified a polymorphic (CA)n repeat (identical to D14S64) within the NRL-containing cosmid, and refined its location by linkage analysis. Since a locus for autosomal recessive retinitis pigmentosa (arRP) has been linked to markers at 14q11 and since mutations in rhodopsin can lead to RP, we sequenced genomic PCR products of the NRL gene and of the rhodopsin-Nrl response element from a panel of patients representing independent families with inherited retinal degeneration. The analysis did not reveal any causative mutations in this group of patients. These investigations provide the basis for delineating the DNA sequence elements that regulate NRL expression in distinct neuronal cell types and should assist in the analysis of NRL as a candidate gene for inherited diseases/syndromes affecting visual function.

Hearing loss in the RBF/DnJ mouse, a proposed animal model of Usher syndrome type IIa

The Usher syndromes (US) are a group of inherited disorders that feature autosomal recessive neurosensory hearing loss or deafness with retinitis pigmentosa (RP). Moderate to severe non-progressive high frequency hearing loss with RP and normal vestibular function describes Usher syndrome type IIa, which has been localized to 1q41. Severe retinal degeneration in the inbred mouse strain RBF/DnJ is caused by rd3, a recessive gene located on mouse chromosome 1 distal to akp1 in a region which is orthologous to human 1q32-q42. We evaluated rd3 as a candidate for orthology with USH2A by first reducing and refining the relatively broad region in which rd3 is thought to reside. DNA of offspring from an RBF/DnJ x MOLF/Ei backcross was genotyped with PCR markers closely flanking the predicted location of rd3. Our haplotype analysis re-positioned rd3 to a 3.6 cM region between markers D1Mit273 (cen) and D1Mit209 (tel), consistent with the expected position of an USH2A murine orthologue. Consequently, rd3 is a positional candidate for Usher type IIa. Next we assessed the rd3/rd3 audiological phenotype to see how closely it paralleled that of Usher IIa. Audiological evaluation of mice at various ages revealed evidence of high frequency progressive hearing loss, previously unreported in the RBF/DnJ strain. However, this newly discovered hearing deficit was observed to be inherited independently of rd3, establishing that a completely different gene is responsible.

Isolation of a novel human homologue of the gene coding for echinoderm microtubule-associated protein (EMAP) from the Usher syndrome type 1a locus at 14q32

Usher syndrome type 1 (USH1) is an autosomal recessive, genetically heterogeneous disorder causing severe congenital deafness, retinitis pigmentosa, and vestibular dysfunction. The USHla locus located on 14q32 has been linked to the genetic markers D14S250 and D14S78. Using D14S250 and D14S78, we have isolated two nonchimeric YACs, 878g10 and 844g2, and a single BAC (135i20) and PAC (194e17) clone and have arranged them into a contig spanning over the D14S250 and D14S78 markers. The analysis of the YACs, BAC, and PAC revealed that the physical distance between D14S250 and D14S78 is less than 25 kb. Iterative cDNA library screening initiated with the EST 219670 found in the vicinity of the D14S78 marker yielded a cDNA contig. The nucleotide sequence of the cDNA encodes a protein of 717 amino acids in length, showing a high level of homology to the Echinoderm 77-kDa microtubule-associated protein (EMAP). The human homologue of Echinoderm microtubule-associated protein defines a novel human gene. We propose that the human EMAP is a strong candidate for the USH1a gene based on its genomic location and the proposed function of the protein.