Haplotype analysis of the USH1D locus and genotype-phenotype correlations

Usher syndrome (USH) is characterised by hearing impairment and progressive pigmentary retinopathy. USH can be divided into three subtypes based on the severity and progression of the major clinical findings. These subtypes are genetically heterogeneous, with at least six loci for USH1, three for USH2 and one for USH3. In the present study, five unrelated consanguineous families with USH1 were analysed for linkage to markers flanking the six USH1 loci. Two of these families, one Pakistani and one Turkish, demonstrated linkage to the USH1D locus. In another family, haplotype segregation was consistent with linkage to USH1C. The remaining families were not linked to any of the six USH1 loci, providing support for the existence of at least one additional USH1 locus. Analysis of these two new USH1D families allowed us to narrow the USH1D candidate region to a 7.3-cM interval with a telomeric flanking marker at D10S1752. Comparison of the affected haplotypes in our Pakistani family with the original Pakistani USH1D family yielded no evidence for a founder effect. The identification of two additional affected families suggests that the USH1D may be a more common form of USH1 than originally suspected. The USH1D (CDH23) gene has recently been cloned. Mutation analysis has shown two different CDH23 mutations in the two Pakistani USH1D families studied, which confirmed our finding that there was no evidence for a founder effect by haplotype analysis. The interesting correlations between genotype and phenotype in CDH23 are also summarised.

IsK and KvLQT1: mutation in either of the two subunits of the slow component of the delayed rectifier potassium channel can cause Jervell and Lange-Nielsen syndrome

The Jervell and Lange-Nielsen syndrome (JLNS) comprises profound congenital sensorineural deafness associated with syncopal episodes. These are caused by ventricular arrhythmias secondary to abnormal repolarisation, manifested by a prolonged QT interval on the electrocardiogram. Recently, in families with JLNS, Neyroud et al. reported homozygosity for a single mutation in KVLQT1 , a gene which has previously been shown to be mutated in families with dominantly inherited isolated long QT syndrome [Neyroud et al . (1997) Nature Genet ., 15, 186-189]. We have analysed a group of families with JLNS and shown that the majority are consistent with mutation at this locus: five families of differing ethnic backgrounds were homozygous by descent for markers close to the KVLQT1 gene and a further three families from the same geographical region were shown to be homozygous for a common haplotype and to have the same homozygous mutation of the KVLQT1 gene. However, analysis of a single small consanguineous family excluded linkage to the KVLQT1 gene, establishing genetic heterogeneity in JLNS. The affected children in this family were homozygous by descent for markers on chromosome 21, in a region containing the gene IsK . This codes for a transmembrane protein known to associate with KVLQT1 to form the slow component of the delayed rectifier potassium channel. Sequencing of the affected boys showed a homozygous mutation, demonstrating that mutation in the IsK gene may be a rare cause of JLNS and that an indistinguishable phenotype can arise from mutations in either of the two interacting molecules.

Mapping of DFN2 to Xq22

Non-syndromic X-linked deafness is a rare form of genetic deafness accounting for a small proportion of all hereditary hearing loss. It is both clinically and genetically heterogeneous and five loci have been described to date but only two of these have been mapped. DFN2 represents a locus for congenital profound sensorineural hearing loss that has yet to be mapped. We describe a four generation family with this phenotype in which female carriers have a mild/moderate hearing loss affecting the high frequencies. The mutant gene has been mapped to Xq22 using polymorphic microsatellite markers. A maximum two point lod score of 2.91 at theta = 0 was observed with a fully informative dinucleotide repeat at COL4A5, and flanking recombinations were observed at DXS990 and DXS1001.

Evaluation of the E2L toy test as a screening procedure in clinical practice

Early identification of hearing loss in young children is essential in order to avoid the potentially disabling effects of deafness. This necessitates effective screening measures with proven positive predictive value (McCormick 1977, 1988; Mahon et al., 1993). Previous studies (Marcuson et al., 1988; Bellman and Marcuson, 1991) have indicated that the E2L Toy Test, designed as a word discrimination test for evaluating the hearing of children who have English as a second language (E2L), could be such a measure. The results of diagnostic audiological testing, including the E2L test, are reported in 264 children. Comparison of E2L results with audiometric testing shows the E2L test to have a sensitivity of 87% and specificity of 90% in identifying children with an average hearing threshold of greater than 25 dB HL (and 78% sensitivity: 94% specificity where the average hearing threshold level is above 20 dB HL). This is the case for both E2L children and for children whose first language is English, suggesting that the E2L Toy Test would be useful in hearing screening test batteries throughout the UK. The results of screening hearing using the E2L Toy Test in 500 children aged 2-7 years from a wide geographical area in the UK are also presented.

Dips on Békésy or audioscan fail to identify carriers of autosomal recessive non-syndromic hearing loss

Békésy and audioscan sweep audiometry tests were carried out in 24 presumed obligate carriers of autosomal recessive non-syndromic hearing loss and 30 sex and age appropriate controls, with a view to defining the most expedient criteria for dips on either test in respect of possible carrier detection. On Békésy, dips with a minimum depth of 22.5 dB generated the greatest difference between carriers and non-carriers, while on audioscan, the criterion of a minimum dip depth of 15 dB provided the best discriminant. Using these criteria, the prevalence of dips was also evaluated in 8 unaffected siblings and 24 age appropriate control subjects. The findings both in the adult and the paediatric groups do not support the hypothesis that the presence of dips, either on Békésy or audioscan, is linked to the carrier state in ARNSHL.

Clinical applications of transcranial bone conduction attenuation in children

It is a common belief that there is no significant transcranial attenuation across the skull by bone conduction (BC). In 32 children with proven unilateral sensorineural hearing loss the unmasked bone thresholds were measured on each side. There was a significant attenuation of BC at 4 kHz. Transcranial attenuation of BC at 4 kHz may explain the difference in sound perception between the two ears when bone conduction amplification is used. Further research should be undertaken to identify the better cochlea in mixed hearing losses.

Neuro-otological function in X-linked hearing loss: a multipedigree assessment and correlation with other clinical parameters

Auditory and vestibular investigations were carried out in 19 affected men and 13 obligate female carriers of 7 pedigrees with nonsyndromic hearing loss segregating as an X-linked trait. In addition, high resolution computerised tomographic scanning was carried out in 24 affected males and 12 obligate female carriers. The neuro-otological results confirm that non syndromic X-linked hearing loss is a clinically heterogeneous condition, but radiological assessment of the cochlea revealed two distinct groups: a normal group, and an abnormal group characterised by a bulbous internal auditory meatus, a dilated facial nerve canal and incomplete separation of the basal coil of the cochlea from the internal auditory meatus. Within a given pedigree there was marked consistency of the presence or absence of the CT scan abnormality in the affected males. One third of the obligate female carriers of the radiologically abnormal pedigrees were shown to have a similar abnormal finding, but as two thirds were normal, radiological examination did not predict carrier status. In the affected men, pure tone audiometric data did not correlate with the radiological abnormality, whereas vestibular function was strikingly correlated, being normal in all but one case in pedigrees with normal radiology and absent, or grossly impaired, in the pedigrees with abnormal radiology. Neuro-otological abnormalities were documented in approximately two thirds of the obligate female carriers, but were insufficiently frequent in occurrence or specific in type to be of predictive value.

Ear-nose-throat abnormalities in the CHARGE association

A comprehensive evaluation of the otolaryngological abnormalities in 50 patients with colobomata, heart defect, atresia of the choanae, retarded growth or development, genital hypoplasia, and ear anomalies or deafness (CHARGE) was performed. All the patients had ear abnormalities; 96% (48/50) had malformed pinnae, and 54% (27/50) had facial nerve palsies. Only 8% (4/50) had normal hearing, the commonest hearing defect being severe conductive or mixed loss. Eighty-four percent (42/50) of computed tomographic scans of the temporal bone were abnormal, the characteristic abnormality being the combination of a hypoplastic incus and absent semicircular canals. Eighty-six percent (43/50) of patients had upper airway abnormalities. Posterior choanal abnormalities occurred in 56% (28/50), and 42% (21/50) had retrognathia leading to intubation difficulties. Laryngotracheal abnormalities occurred in 38% (19/50), and 14% (7/50) required tracheostomies. Careful upper airway assessment is essential to avoid potentially lethal complications such as aspiration.

Clinical and genetic heterogeneity in X-linked deafness

The use of molecular techniques in respect of the rare X-linked non-syndromic form of genetic deafness demonstrates that this is a genetically heterogeneous disorder, with evidence for at least two separate gene loci on the X chromosome. Audiological heterogeneity in this condition is emphasized by the observation of both mixed deafness and sensorineural deafness in pedigrees showing evidence for linkage to Xq13-q21. The importance and shortcomings of the audiogram in assessing females who are known gene carriers is discussed.

A multipedigree linkage study of X-linked deafness: linkage to Xq13-q21 and evidence for genetic heterogeneity

A locus for X-linked nonsyndromic deafness has previously been allocated to the Xq13-q21 region based on linkage studies in two separate pedigrees. This has been substantiated by the observation of deafness as a clinical feature of male patients with cytogenetically detectable deletions across this region. The question of a second locus for deafness in this chromosomal region has been raised by the audiologically distinct nature of the deafness in some of the deleted patients compared to that observed in those patients upon whom the linkage data are based. We have performed detailed clinical evaluation and linkage studies on seven pedigrees with nonsyndromic X-linked deafness and conclude that there is evidence for at least two loci for this form of deafness, including one in the Xq13-q21 region. We have observed different radiological features among the pedigrees which map to Xq13-q21, suggesting that even among these pedigrees the deafness is due to different pathological processes. Given these findings, we suggest that the classification of nonsyndromic X-linked deafness based solely on audiological criteria may need to be reviewed.

A new toy test to investigate the hearing status of young children who have English as a second language: a preliminary report

The aim of this study was to produce a word list suitable for children aged between 2 and 6 years with English as a second language (E2L) to be used in the format of a toy test to evaluate hearing status. Two lists of English words were compiled using words previously shown to be among the early English words learned by children from the Indian sub-continent. These word lists were evaluated in a group of 56 children who had recently arrived from Bangladesh. The results of this study yielded a final word list of 12 words, arranged into six pairs of words with matched vowels. This final word list, used in the E2L Toy Test, is currently being evaluated in a multi-centre study, for children between the ages of 3 and 6 years.

X-linked deafness, stapes gushers and a distinctive defect of the inner ear

The association of X-linked mixed deafness with stapes gusher has been recognized for 20 years, and imaging studies by polytomography have shown dilatation of the lateral end of the internal auditory meatus (IAM) in some cases. We have made genetic linkage studies in 7 pedigrees in whom deafness was inherited in an X-linked manner. All patients had a full range of audiometric and vestibular function tests. Thin section high resolution CT in two planes was used to assess the state of the middle and inner ears. We found a distinctive inner ear deformity in some of the deaf males characterised not only by a wide bulbous IAM but more importantly, by deficient or absent bone between the lateral end of the IAM and the basal turn of the cochlea. We believe that this results in a communication between the subarachnoid space in the IAM and the perilymph in the cochlea, leading to perilymphatic hydrops and a "gusher" if the stapes is disturbed. Moreover, some of the obligate female carriers seem to have a milder form of the same anomaly associated with slight hearing loss. Genetic studies on some of the deaf males with apparently normal inner ear anatomy suggest a different locus on the X chromosome and hence a different pathogenesis for the deafness.

Outcome of preterm infants who suffered neonatal apnoeic attacks

Thirty infants of less than 31 weeks post-menstrual age were monitored for apnoea using routine medical equipment and intermittent 24-h pneumocardiograms. These infants were examined again between 16 and 36 months of age. Full physical and ophthalmological examinations were carried out as well as audiometry and assessment using the Griffiths mental developmental scales. Twenty-five of these infants had suffered apnoeic attacks and two of these infants had an abnormal developmental quotient. Neither sensorineural deafness of retinopathy of prematurity were detected in the children who suffered apnoeic episodes. The poor prognosis which has been associated with neonatal apnoea may not apply to those infants without other serious neonatal problem.

A nine-year review of 841 children tested by transtympanic electrocochleography

The case notes of 841 subjects who had had ECochG carried out between January 1972 and December 1980, were examined and the results compared with PTA results in 263 cases in which these were available. ECochG was found to be a good predictor of peripheral hearing as long as its limitations were recognized, and some of these are discussed. BSER, which has similar limitations, was also found to be a good predictor of peripheral hearing, although slightly less sensitive, and sometimes gave additional information on the hearing loss and the clinical state of the patient.