Genetic Linkage Analysis of 15 DFNB Loci in a Group of Iranian Families with Autosomal Recessive Hearing Loss

BACKGROUND

Hearing loss (HL) is the most frequent sensory birth defect in humans. Autosomal recessive non-syndromic HL (ARNSHL) is the most common type of hereditary HL. It is extremely heterogeneous and over 70 loci (known as DFNB) have been identified. This study was launched to determine the relative contribution of more frequent loci in a cohort of ARNSHL families.

METHODS

Thirty-seven Iranian families including 36 ARNSHL families and 1 family with Pendred syndrome each with ≥ 4 affected individuals, from seven provinces of Iran, were ascertained. DFNB1 contribution was initially studied by DNA sequencing of GJB2 and linkage analysis using the relative STR markers. The excluded families were then subjected to homozygosity mapping for fifteen ARNSHL loci.

RESULTS

Sixteen families were found to be linked to seven different known loci, including DFNB1 (6 families), DFNB4 (3 families +1 family with Pendred syndrome), DFNB63 (2 families), DFNB2 (1 family), DFNB7/11 (1 family), DFNB9 (1 family) and DFNB21 (1 family). DNA sequencing of the corresponding genes is in progress to identify the pathogenic mutations.

CONCLUSION

The genetic causes were clarified in 43.2% of the studied families, giving an overview of the causes of ARNSHL in Iran. DFNB4 is ranked second after DFNB1 in the studied cohort. More genetic and epigenetic investigations will have to be done to reveal the causes in the remaining families.

Single-nucleotide polymorphisms in the COL1A1 regulatory regions are associated with otosclerosis

Otosclerosis (MIM 166800) has a prevalence of 0.2-1% among white adults, making it the single most common cause of hearing impairment in this ethnic group. Although measles virus, hormones, human leukocyte antigen alleles and genetic factors have been implicated in the development of otosclerosis, its etiology remains unknown. In a focused effort to identify genetic factors in otosclerosis, we have mapped four disease loci (MIM 166800/605727/608244/608787); however, cloning the disease-causing genes in these intervals has not been successful. Here, we used a case-control study design to investigate the association between collagen type I genes and otosclerosis. We identified susceptibility and protective haplotypes in COL1A1 that are significantly associated with otosclerosis in the Caucasian population. These haplotypes alter reporter gene activity in an osteoblast cell line by affecting binding of transcription factors to cis-acting elements. Our data suggest that increased amounts of collagen alpha1(I) homotrimers are causally related to the development of otosclerosis. Consistent with this hypothesis, mouse mutants homozygous for a Col1a2 frameshift mutation on a C57BL/6J background that deposit only homotrimeric type I collagen have hearing loss.

[From gene to disease; non-syndromic, autosomal dominant, low-frequency sensorineural hearing loss (DFNA6/14)]

DFNA6/-14 is a nonsyndromic, autosomal dominant form of hearing impairment that is characterised by low-frequency sensorineural hearing loss, which in some cases is progressive. It is the only known form of dominantly inherited low-frequency hearing impairment in the Netherlands. It is caused by heterozygous non-inactivating mutations in the WFSI gene, which are also present in the Wolfram or DIDMOAD syndrome.

Longitudinal and cross-sectional phenotype analysis in a new, large Dutch DFNA2/KCNQ4 family

We analyzed hearing thresholds, speech recognition scores, and vestibular responses in 32 affected persons in a large family with DFNA2/KCNQ4-related hearing impairment caused by a W276S missense mutation. Linear regression analysis of individual longitudinal data revealed significant threshold progression (1 dB/y) and offset (at age zero). The mean offset thresholds were 5, 21, 40, 39, 31, and 51 dB hearing level (HL) at 0.25, 0.5, 1, 2, 4, and 8 kHz, respectively. Cross-sectional analysis of last-visit thresholds against age produced less-steep slopes and higher offset thresholds. Nonlinear regression analysis of last-visit phoneme recognition scores against age in 25 cases showed that speech recognition did not deteriorate before the third decade. A hyperactive vestibuloocular reflex was found in 3 of 11 cases: 2 persons were especially susceptible to motion sickness. Persons with this KCNQ4 mutation showed congenital, progressive high-frequency impairment without substantial loss of speech recognition during the first decades of life.

Progressive hearing loss, hypoplasia of the cochlea and widened vestibular aqueducts are very common features in Pendred's syndrome

Long-term hearing threshold-on-age follow-up data, including non-linear regression analysis, are given for 12 consecutive Pendred patients. The clinical diagnosis of Pendred's syndrome was confirmed by a mutation analysis of the PDS gene in 11 out of the 11 cases tested. Recent imaging of the temporal bones in seven out of these 12 patients showed widened vestibular aqueducts in each case. The diagnostic perchlorate test was negative in one patient, but this test was positive in her affected sister. Mutation analysis of the PDS gene in these patients confirmed that Pendred's syndrome is a monogenetic disorder. Progressive sensorineural hearing loss and widened vestibular aqueducts are characteristic features of Pendred's syndrome, which provides the opportunity to diagnose Pendred's syndrome clinically in the first few years of life, as has recently been suggested in a case report (Cremers et al., Progressive sensorineural hearing loss and a widend vestibular aqueduct in Pendred syndrome, Arch. Otolaryngol. 124 (1998) 501-505). Mutation analysis of the involved gene can be used to confirm the clinical diagnosis.

Early-onset sensorineural hearing loss and late-onset neurologic complaints caused by a mitochondrial mutation at position 7472

OBJECTIVES

To detect a mitochondrial mutation responsible for maternally transmitted hearing loss with late-onset neurologic features in a 3-generation Dutch family, and to describe the hearing loss, associated symptoms, and vestibular dysfunction.

PATIENTS AND METHODS

All maternally related family members (n = 69) were investigated using standard audiometry. In a selected group, vestibulo-ocular examinations and additional neurologic and ophthalmologic examinations were performed. Twenty milliliters of venous blood was taken from all participants for genetic studies.

SETTING

University medical center.

RESULTS

All maternally related individuals carried an extra C at position 7472 of the mitochondrial genome. Hearing loss was the only symptom or presenting symptom in most family members and most pronounced at higher frequencies. Hearing loss at lower frequencies was demonstrated in individuals 10 years and older. Most patients had vestibular hyperreactivity and were susceptible to motion sickness, suggesting vestibulocerebellar dysfunction. Neurologic complaints were infrequent and presented by older individuals; however, numerous enlarged mitochondria were found in a muscle biopsy specimen of an individual with hearing impairment but without neurologic symptoms.

CONCLUSIONS

Respiratory chain dysfunction should be considered as a possible cause of progressive sensorineural hearing loss. More research into the causes of high-frequency impairment should be considered, especially when sensorineural hearing loss, syndromal or nonsyndromal, is exclusively maternally transmitted. Maternal transmission of hearing impairment can also be valuable in the diagnosis of unclear neurologic syndromes.

Familial congenital hydrocephalus and aqueduct stenosis with probably autosomal dominant inheritance and variable expression

A kindred is reported on with suspected autosomal dominant congenital hydrocephalus and aqueduct stenosis. In contrast to patients with X-linked congenital hydrocephalus with stenosis of the aqueduct of Sylvius (HSAS) our patients were not mentally retarded and they did not show any pyramidal tract dysfunction or clasped thumbs; the pyramids were not affected either, as was confirmed by autopsy, CT or MRI. Molecular genetic studies in our patients have not revealed abnormalities of eight exons of the L1 neural adhesion molecule gene that is related to HSAS.

Inherited nonsyndromic hearing loss. An audiovestibular study in a large family with autosomal dominant progressive hearing loss related to DFNA2

OBJECTIVE

To study nonsyndromic progressive sensorineural hearing loss (SNHL) with significant linkage to the DFNA2 locus on chromosome 1p in a Dutch kindred.

DESIGN

A 6-generation family with 194 family members was studied. Of the presumably affected persons, 43 were examined in detail to obtain audiograms and 37 underwent vestibulo-ocular examination.

RESULTS

Regression analysis showed significant and equal linear progression in SNHL with age (by about 1 dB per year) at all frequencies. Offset values were close to zero at the low frequencies (0.25, 0.5, and 1 kHz) but increased systematically with the frequency. It is likely that they represent congenital high-frequency SNHL: about 15 dB at 2 kHz, 30 dB at 4 kHz, and 50 dB at 8 kHz. Bilateral caloric weakness was not observed. A significant finding was that 25% to 35% (depending on the exclusion criteria) of the patients showed an increased vestibulo-ocular reflex (hyperreactivity) as measured by rotatory responses. Forty-one patients showed significant linkage to the 1p locus.

CONCLUSIONS

Including the present family, 4 families have been reported to show linkage to chromosome 1p. Statistical analysis of the audiological data shows a progression of 1 dB per octave per year in this type of progressive SNHL.

Localization of a gene for non-syndromic hearing loss (DFNA5) to chromosome 7p15

Progressive hearing loss affects approximately 50% of the elderly by the age of 80, and is most likely caused by an interaction of genetic and environmental factors. Identification of the genes responsible for hereditary hearing loss is therefore important. Families with pure genetic degenerative hearing disorders may be helpful as the same genes may be also involved in age-related hearing loss in general. In this study we have performed a genome search in an extended Dutch family with autosomal dominant progressive hearing loss starting in the high frequencies. The gene causing hearing loss in this family was localized to the short arm of chromosome 7, in a 15 cM interval between markers D7S493 and D7S632.

Effect of respiration on Doppler parameters of normal tricuspid porcine bioprosthetic valves

The Doppler indexes of tricuspid porcine bioprosthetic valves were evaluated in twelve patients without clinical and two-dimensional echocardiographic evidence of valve dysfunction. Peak and mean pressure gradients across the prostheses were measured using the simplified Bernoulli equation. All the Doppler measurements were compared during inspiration and expiration. During inspiration peak velocity, peak gradient and mean gradient (1.52 +/- 0.28 m/s; 9.7 +/- 3.05 mmHg; 4.07 +/- 1.16 mmHg) were significantly higher than during expiration (1.28 +/- 0.8 m/s; 6.58 +/- 2.7 mmHg; 2.98 +/- 1.13 mmHg; p < 0.01) but pressure half time was not significantly different (122 +/- 62 ms versus 134 +/- 75 ms; p > 0.05). Inspiratory range of peak velocities, peak gradients, mean gradients and pressure half times were respectively 0.8-2.04 m/s; 4.9-16.6 mmHg; 1.2-7.2 mmHg; 42-340 ms while expiratory range of values was 0.8-1.93 m/s; 2.6-15 mmHg; 1.1-5.7 mmHg; 46-345 ms. These data suggest that even very long pressure half times do not indicate valve dysfunction. This study demonstrates that large variation of Doppler parameters are present during respiration and could produce inaccuracy in the assessment of bioprostheses in tricuspid position if they are not taken in consideration.