Alport's syndrome: can carriers be identified by audiometry?

Comprehensive molecular-genetic analysis of mid-frequency sensorineural hearing loss

The genetic heterogeneity of sensorineural hearing loss (SNHL) is a major hurdle to the detection of disease-causing variants. We aimed to identify underlying causal genes associated with mid-frequency hearing loss (HL), which contributes to less than about 1% of SNHL cases, by whole exome sequencing (WES). Thirty families segregating mid-frequency SNHL, in whom biallelic GJB2 mutations had been previously excluded, were selected from among 851 families in our DNA repository of SNHL. DNA samples from the probands were subjected to WES analysis and searched for candidate variants associated with SNHL. We were able to identify the genetic aetiology in six probands (20%). In total, we found three pathogenic and three likely pathogenic variants in four genes (COL4A5, OTOGL, TECTA, TMPRSS3). One more proband was a compound heterozygote for a pathogenic variant and a variant of uncertain significance (VUS) in MYO15A gene. To date, MYO15A and TMPRSS3 have not yet been described in association with mid-frequency SNHL. In eight additional probands, eight candidate VUS variants were detected in five genes (DIAPH1, MYO7A, TECTA, TMC1, TSPEAR). Seven of these 16 variants have not yet been published or mentioned in the available databases. The most prevalent gene was TECTA, identified in 23% of all tested families. Furthermore, we confirmed the hypothesis that a substantive portion of cases with this conspicuous audiogram shape is a consequence of a genetic disorder.

Severe to profound hearing loss in patients with progressed Alport's syndrome

CONCLUSION

The concept of hearing loss severity must be redefined, as there is a clear need for more active hearing management in Alport's syndrome patients with severe and profound hearing loss.

OBJECTIVES

Sensorineural hearing loss (SNHL) caused by Alport's syndrome generally does not exceed 60-70 dB, because a cochlear lesion is responsible for this hearing loss. Careful management of renal function improves the prognosis and the longevity of Alport's syndrome patients; it is useful to reassess SNHL caused by Alport's syndrome.

PATIENTS AND METHODS

Thirty-two patients with Alport's syndrome were analyzed retrospectively. Pure tone audiograms (PTAs), speech audiograms, and transiently evoked otoacoustic emissions (TEOAEs) were performed. Hearing loss severity was compared to duration of disease and severity of renal dysfunction. We also evaluated the correlation between OAEs and PTAs according to the hypothesis that evoked OAEs would be abnormal even in early stage SNHL in Alport's syndrome.

RESULTS

The level of hearing was positively correlated with disease duration. The hearing of the end-stage renal disease (ESRD) group, whose hearing threshold could exceed 70 dB, was worse than that of the non-ESRD group. OAEs were found in patients with normal hearing and mild hearing loss and had no significant early detection value.

Revisão sobre a perda auditiva na Síndrome de Alport, analisando os aspectos clínicos, genéticos e biomoleculares

A Síndrome de Alport é uma desordem hereditária, caracterizada por hematúria, freqüentemente levando à falência renal. Pode ser acompanhada de alterações extra-renais, tais como: perda auditiva (PA) sensório-neural e alterações oculares. São descritas formas dominantes ligadas ao X, devidas às mutações no lócus COL4A5 e uma forma autossômica recessiva resultando de mutações no lócus COL4A3 ou COL4A4. Ainda foi sugerido um tipo autossômico dominante de SA. A doença decorre de alterações nas cadeias de colágeno tipo IV e os sintomas refletem o comprometimento da membrana basal de vários órgãos. As redes alfa3.alfa4.alfa5(IV) ocorrem no rim, na cóclea e no olho. O objetivo foi caracterizar a PA neste grupo de pacientes. Quando o quadro progride para o estágio final de falência renal, o melhor método de tratamento é o transplante, que tem contribuído para o aumento da sobrevida. Nesta revisão bibliográfica, observamos que: 1. A SA caracteriza-se por hematúria, que evolui para falência renal e pode ser acompanhada de manifestações extra-renais. A PA é um achado extra-renal freqüente e um dos primeiros sintomas na SA, sendo um fator relevante para o prognóstico da evolução da doença renal; 2. A SA é genética e decorre da alteração das cadeias do colágeno tipo IV nas membranas basais; 3. A perda auditiva na SA é sensório-neural, de intensidade variável, progressiva e simétrica. Acomete as freqüências médias e altas; 4. Na investigação das perdas auditivas, o otorrinolaringologista deve incluir um exame de urina. É fundamental que o otologista atue no acompanhamento deste grupo de pacientes.

Revision about hearing loss in the Alport's syndrome, analyzing the clinical, genetic and bio-molecular aspects

Alport Syndrome is a genetic disorder characterized by hematuria, which often leads to renal failure. It may also be accompanied by extra-renal alterations, such as: sensorineural hearing loss, and ocular abnormalities. Dominant forms related to the X chromosome and caused by mutations in the locus COL4A5 have been described, as well as an autossomic recessive form resulting from mutations in the locus COL4A3 or COL4A4. An autossomic dominant type of AS has also been reported. The disease is caused by changes in the collagen type IV chains, where symptoms reflect the damage to the basal membrane of several organs. The α3.α4.α5(IV) networks are found in the kidneys, cochlea and eyes. The objective was to characterize AS in this group of patients. In the current literature review it was found that: 1. AS is characterized by hematuria that may develop into renal failure and can also be accompanied by extra-renal manifestations. Hearing loss is a frequent extra-renal finding and one of the first symptoms of AS, therefore representing a relevant factor in the prognosis of the renal disease; 2. It is a genetic disorder resulting from abnormalities in the chains of collagen type IV in the basal membranes; 3. The hearing loss in AS is typically sensorineural with variable intensities, progressive and symmetrical, affecting middle and high frequencies; 4. Otolaryngologists should include a urine test in the SNHL work-up. It is essential to have an otologist involved in the treatment of these patients.

The Audioscan: a high frequency resolution audiometric technique and its clinical applications

The Audioscan is a form of high definition audiometry based on iso-hearing level frequency sweeps, which was developed by Meyer-Bisch in 1990. Compared with traditional tone audiometry, it sweeps across the preset frequency range at a predetermined sweep rate and provides a continuous audiometric curve. Because the device has a maximum frequency range of 125-16 000 Hz with 64 frequencies per octave, the Audioscan method can, theoretically, give 64 times as many values as fixed-frequency audiometry, which may give greater accuracy and sensitivity. An advantage of this is its capacity to detect mild audiometric deficits such as narrow notches situated between the frequencies normally tested. These may represent very limited auditory lesions, at a stage when they cannot be detected by routine audiological methods. Thus, the Audioscan method can give not only a detailed audiometric curve, but also provide important indicators of mild auditory dysfunction. The Audioscan device (e.g. Essilor model) is commercially available for clinical purpose. It is a software-based system, which can also be used for pure tone audiometry and Békésy audiometry. This paper reviews the general aspects of the Audioscan technique and current applications for detecting auditory dysfunction. This would be valuable to provide some guidelines on the Audioscan assessment, and contribute to a clarification of the clinical application of Audioscan and facilitate further research.

Alport syndrome: a review

Alport syndrome, a hereditary nephritis accompanied by high-tone sensorineural deafness and distinctive ocular signs was first noted in the literature during the early 1900s. This disease is caused by a genetic defect in Type IV collagen which makes up basement membranes in many body systems. The patient will usually have bilateral anterior lenticonus causing varied refractive errors. You may also note yellow-white to silver flecks within the macular and midperipheral regions of the retina. The treatment of the visual problems is an important but secondary concern due to the seriousness of the systemic disease. Dual sensory loss, however, creates an urgent need for appropriate vision care. Due to the high risk for developmental delay and decreased social integration, early intervention should be considered in the treatment plan. Coping strategies for the patient (and the family) need to be addressed because of the chronicity of this syndrome. The primary care optometrist will be challenged by the individual with Alport syndrome since a balance between oculo-visual, developmental/psycho-educational and systemic care is required. A multi-disciplinary approach by the healthcare management team will enhance the quality of life and positive outcomes for these patients.

A particular case of deafness-oligodontia syndrome

Two previous case reports described two sibs affected with both sensorineural hearing loss and oligodontia. Here, we report a similar syndrome in a male patient with an, as yet, undescribed vestibular aqueduct enlargement on tomodensitometry. The analysis of the parent's audiograms is consistent with the suggested autosomal recessive mode of inheritance of this disorder.

Application of the Audioscan in the detection of carriers of genetic hearing loss

The authors describe the establishment of normative stimulus parameters for the Audioscan, an automated sweep frequency audiometer, for its application in the detection of audiometric notches in carriers of recessive genetic hearing loss. A sweep rate of 30 s/octave over the frequency range 300 to 4000 Hz pulsing at 2.5 pulses/s at -5 dB with a step size of 5 dB were ultimately adopted. The criterion for notches was 15 dB or greater within the frequency range 500-3000 Hz. Adopting this criterion, 14.2% of control subjects had notches. Among parents of children with non-syndromal recessive hearing loss 55% were found to have notches. Notches were found more frequently among mothers and sisters than among fathers and brothers of the patients.