Association of COL1A1 polymorphism in Turkish patients with otosclerosis

OBJECTIVE

To evaluate the role of COL1A1 gene polymorphism in the etiology of otosclerosis.

MATERIAL AND METHODS

Peripheric blood samples are obtained from 28 patients diagnosed with otosclerosis and 50 control subjects. DNA's of all samples are isolated and amplified by using the PCR technique. The products are restricted by appropriate enzymes and the allele distributions were compared.

RESULTS

SS (homozygous normal), Ss (heterozygous mutant) and ss (homozygous mutant) alleles of the otosclerotic and control subjects were significantly different from each other.

CONCLUSION

Otosclerosis is a disease with progressive hearing loss. There are viral, hormonal, immunologic and genetic hypothesis of etiology. In this study, we concluded that the polymorphism seen in the COL1A1 gene resulting in production of excessive type 1 collagen, could play a role in the pathogenesis of otosclerosis.

The effects of angiotensin II and the oxidative stress mediator 4-hydroxynonenal on human osteoblast-like cell growth: possible relevance to otosclerosis

Otosclerosis is a complex disease characterized by an abnormal bone turnover of the otic capsule resulting in conductive hearing loss. Recent findings have shown that angiotensin II (Ang II), a major effector peptide of the renin-angiotensin system, plays an important role in the pathophysiology of otosclerosis, most likely by its proinflammatory effects on the bone cells. Because reactive oxygen species play a role both in inflammation and in the cellular signaling pathway of Ang II, the appearance of protein adducts of the "second messenger of free radicals," the aldehyde 4-hydroxynonenal (HNE), in otosclerotic bone has been analyzed. Immunohistochemical analysis of HNE-modified proteins in tissue samples of the stapedial bones performed on 15 otosclerotic patients and 6 controls revealed regular HNE-protein adducts present in the subperiosteal parts of control bone specimens, whereas irregular areas of a pronounced HNE-protein adduct presence were found within stapedial bone in cases of otosclerosis. To study possible interference by HNE and Ang II in human bone cell proliferation, differentiation, and induction of apoptosis we used an in vitro model of osteoblast-like cells. HNE interacted with Ang II in a dose-dependent manner, both by forming HNE-Ang II adducts, as revealed by immunoblotting, and by modifying its effects on cultured cells. Namely, treatment with 0.1 nM Ang II and 2.5 μM HNE stimulated proliferation, whereas treatment with 10 μM HNE or in combination with Ang II (0.1, 0.5, and 1 nM) decreased cell proliferation. Moreover, 10 μM HNE alone and with Ang II (except if 1 nM Ang II was used) increased cellular differentiation and apoptosis. HNE at 5 μM did not affect differentiation nor significantly change apoptosis. On the other hand, when cells were treated with lower concentrations of HNE and Ang II we observed a decrease in cellular differentiation (combination of 1.0 or 2.5 μM HNE with 0.1 nM Ang II) and decrease in apoptosis (0.1 and 0.5 nM Ang II). Cellular necrosis was increased with 5 and 10 μM HNE if given alone or combined with Ang II, whereas 0.5 nM Ang II and combination of 1 μ M HNE with Ang II (0.1 and 0.5 nM) reduced necrosis. These results indicate that HNE and Ang II might act mutually dependently in the regulation of bone cell growth and in the pathophysiology of otosclerosis.

Defective postnatal endochondral bone development by chondrocyte-specific targeted expression of parathyroid hormone type 2 receptor

The human parathyroid hormone type 2 receptor (PTH2R) is activated by PTH and by tuberoinfundibular peptide of 39 residues (TIP39), the latter likely acting as its natural ligand. Although the receptor is expressed at highest levels in the nervous system, we have observed that both PTH2R and TIP39 are expressed in the newborn mouse growth plate, with the receptor localizing in the resting zone and the ligand TIP39 localizing exclusively in prehypertrophic and hypertrophic chondrocytes. To address the role of PTH2R in postnatal skeletal growth and development, Col2a1-hPTH2R (PTH2R-Tg) transgenic mice were generated. The mice were viable and of nearly normal size at birth. Expression of the transgene in the growth plate was limited to chondrocytes. We found that chondrocyte proliferation was decreased, as determined by in vivo BrdU labeling of proliferating chondrocytes and CDK4 and p21 expression in the growth plate of Col2a1-hPTH2R transgenic mice. Similarly, the differentiation and maturation of chondrocytes was delayed, as characterized by decreased Sox9 expression and weaker immunostaining for the chondrocyte differentiation markers collagen type II and type X and proteoglycans. As well, there was altered expression of Gdf5, Wdr5, and β-catenin, factors implicated in chondrocyte maturation, proliferation, and differentiation.These effects impacted on the process of endochondral ossification, resulting in delayed formation of the secondary ossification center, and diminished trabecular bone volume. The findings substantiate a role for PTH2R signaling in postnatal growth plate development and subsequent bone mass acquisition.

Expression of bone morphogenetic protein 2, 4, 5, and 7 correlates with histological activity of otosclerotic foci

CONCLUSION

This study is the first to establish that bone morphogenetic protein 5 (BMP5) plays a role in the pathogenesis of otosclerosis. These results confirm that elevated expression levels of BMPs, members of the transforming growth factor (TGF)-β superfamily, contribute to the pathologically increased bone turnover in early, active stages of otosclerosis.

OBJECTIVES

Otosclerosis is a complex bone remodeling disorder of the otic capsule, which might be characterized by increased expression of different types of BMPs. TGF-β and BMP are both members of the TGF-β superfamily and play a critical role in bone resorption and new bone formation. It has been suggested that BMP and its receptors may be involved in the pathologically increased bone turnover observed in otosclerosis.

METHODS

Fifty-one otosclerotic and 16 non-otosclerotic ankylotic stapes footplates were histologically analyzed: conventional hematoxylin-eosin staining and BMP2, 4, 5, and 7specific immunofluorescent assays were performed. Cortical bone fragments (n = 35) and incus specimens (n = 6) were used as negative controls.

RESULTS

Active otosclerosis (n = 39) was characterized by increased expression of BMP2, 4, 5, and 7. Inactive cases of otosclerosis (n = 12) were characterized by negative immunoreaction for BMPs. Non-otosclerotic stapes specimens (n = 16) and negative controls (n = 41) showed negligible BMP expression. The BMP expression pattern showed a strong correlation with the histological activity of otosclerosis.

Otosclerosis: a perilabyrinthine threshold phenomenon

This paper is a review of our most recent findings concerning the osteo-dynamics of the bony otic capsule and pathogenesis of otosclerosis. By exploring the spatial relationship between normal perilabyrinthine bone remodeling, the viability and spatial distribution of labyrinthine osteocytes, and the location of otosclerosis, a unique spatial pattern emerged. Bone remodeling is highly inhibited around the inner ear space. Most likely, inner ear anti-resorptive signals enter the bony otic capsule through the lacuno-canalicular porosity. The patency of this signaling pathway depends on the viability of individual osteocytes. In the young otic capsule the density of viable osteocytes is high and centripetally distributed. This arrangement may sustain a life-long osseus pathway for anti-resorptive signals even within a bone where a considerable loss of viable osteocytes must be expected, as demonstrated by a centripetal accumulation of dead osteocytes with age. The spatial distribution of dead osteocytes follows the same general pattern as otosclerosis. We suggest that clustering of dead osteocytes may impede the transmission of anti-resorptive signals locally, leaving such ghost regions susceptible to focal bone remodeling as in human otosclerosis. The preserved network of viable osteocytes around the depleted ghost regions may contain the process and distort the structure of bone remodeling into an abnormal otosclerotic pattern.

[Otosclerosis- <<the mysterious sphinx>> or the loss of the natural variant of inertness (<<bradytrophicity>> of the labyrinth capsule)]

The author suggests an original hypothesis of otosclerosis based on the analyses of the literature publications for many years and his personal clinical observations. The normal labyrinth capsule is considered to be bradytrophic, i.e. inert and showing an extremely low level of metabolic processes. The disturbance of bradytrophicity under the action of individual factors and/or especially their combination make it involved in the maintenance of calcium homeostasis in the body. The validity of this conjecture is confirmed by the results of histological investigations, viz. the appearance of diquide or xplasma-like, bone in the labyrinth of the patients suffering otosclerosis. Such bone resorption is known to occur in other parts of the bony skeletontoo and should be regarded as a normal physiological process contributing to the replenishment of blood calcium deficiency.The subsequent reorganization (remodeling) of any part of the bony skeleton is physiologically neutral. In the labyrinth capsule,with its small size and delicate structure, such reorganization induces the otosclerotic process responsible for dysfunction of the membranaceous labyrinth. The surgical treatment of the patients presenting with otosclerosis should be supplemented by conservative treatment intended to slow down the otosclerotic reorganization and to restore bradytrophicity of the labyrinth capsule.

Reactive oxygen species in human inner ear perilymph

CONCLUSIONS

The results reported here provide the first evidence of the production of superoxide, a biologically relevant reactive oxygen species (ROS), in human inner ear perilymph (hIP) in pathological conditions, by the activity of the xanthine dehydrogenase/xanthine oxidase (XA/XO) enzyme system.

OBJECTIVE

To investigate the presence of ROS in hIP.

METHODS

Since damage and apoptosis of inner ear hair cells may occur as a result of ROS-mediated injury, we investigated the presence and production of ROS in 105 hIP samples; 98 collected from patients affected by profound sensorineural hearing loss, during surgery for cochlear implantation, and 7 controls, collected from patients affected by otosclerosis, in case of spontaneous leakage after stapedotomy. ROS production was investigated by spectrophotometric analysis and polyacrylamide gel electrophoresis (SDS-PAGE).

RESULTS

In hIP samples tested by cytochrome c reduction kinetics, the average superoxide production was 27.34 mumoles per mg of total protein, against 0.36 in controls. Some of these hIP samples, analyzed by cytochrome c reduction kinetics in the presence of xanthine, were found to be positive for ROS-producing XA/XO enzyme. These results were supported by SDS-PAGE analysis.

Otosclerosis: an organ-specific inflammatory disease with sensorineural hearing loss

Otosclerosis is an inflammatory disease associated with persistent measles virus (MV) infection of the otic capsule. The nature of sensorineural hearing loss (SNHL) related to otosclerosis can be due to the chronic TNF-alpha release from the foci. TNF-alpha enters the inner ear fluid spaces in histologically active stages of otosclerosis and may cause outer hair cell functional disorder and subsequent SNHL without morphological changes of the organ of Corti. On the contrary, non-otosclerotic stapes ankylosis being a non-inflammatory disease is not harmful for hair cells. Theoretically, SNHL should not associate to this type of stapes fixation. Stapes footplates (N = 248) were examined by hematoxylin-eosin staining and corresponding MV-, OPG- and TNF-alpha-specific RT-PCR. Anti-measles IgG levels of serum specimens were measured by ELISA. Preoperative audiological results were correlated with otosclerotic and non-otosclerotic histopathologies. Among patients with stapes fixation, we found 93 active and 67 inactive otosclerosis, and 88 non-otosclerotic stapes ankylosis. MV could only be detected in otosclerotic stapes footplates. Audiometry revealed bone conduction threshold elevation toward the high frequencies in otosclerotic patients, which was associated to the duration of hearing loss. OPG mRNA expression was significantly lower in the TNF-alpha positive specimens, which was independent from virus positivity. In about one-third of stapes fixations, the etiology is non-otosclerotic stapes ankylosis. Histologic otosclerosis exhibits a strong correlation with MV presence in the bone as a sign of persistent MV infection and related inflammation with TNF-alpha release. This causes SNHL in the function of time. Non-otosclerotic stapes fixations do not cause high-frequency SNHL.

Signaling by way of type IB and II bone morphogenetic protein receptors regulates bone formation in otospongiosis

HYPOTHESIS

The main goal of this study was to perform an immunohistologic analysis of bone morphogenetic protein receptors (BMPR) in otospongiosis.

BACKGROUND

BMP-2, -4, and -7 play an essential role in bone formation and repair. They do so as well in otosclerosis. It has been shown that these BMPs are traceable in osteocytes and osteoclasts in the active phase of otosclerosis (otospongiosis). The role of the different BMP receptors in otosclerotic bone transformation has not been previously analyzed.

METHODS

The posterior parts of the stapes footplates, collected during partial stapedectomies in 35 patients with clinical otosclerosis, were analyzed for histologic otosclerotic lesions after hematoxylin staining. Immunohistochemical analysis was performed using polyclonal immunoglobulin G antibodies for BMPR-IA, -IB, and -II, as well as biotinylated secondary antibodies, avidin-biotin-peroxidase complex reaction, and alkaline phosphatase staining with nitroblue-tetrazolium-chloride.

RESULTS

Seventeen of 35 (49%) specimens contained otosclerosis, but only 5 of these exhibited an otospongiotic phase. The abundant osteoblasts and osteoclasts in these cases showed distinct immunochemical staining for BMP-2, -4, and -7. In two cases, there could also be found an immense positive staining for BMPR-IB and modest staining for BMPR-II, whereas BMPR-1A always remained negative.

CONCLUSION

It was demonstrated for the first time that in otospongiosis, the actions of the BMPs are mediated through BMPR-IB and BMPR-II. To determine this role in detail, further investigations, especially for the phosphorylated Smad proteins within the BMP dependent mediator cascade, will be necessary.

Is there a relationship between myringosclerosis and atherosclerosis?

OBJECTIVE

Myringosclerosis and atherosclerosis are two different pathologies seen in different parts of the body. Both of these occur following a similar physiopathological process. However this has not previously been adequately discussed in the literature. Trauma to either the tympanic membrane or to the intimal layer of the arterial wall results in the formation of a sclerotic plaque. The goal of this study was to investigate the relationship between myringosclerosis and atherosclerosis.

PATIENTS

A total of 421 patients with the diagnosis of coronary artery disease were included in the study. All of the patients were evaluated for the presence of atherosclerosis by coronary angiography and for myringosclerosis by otoscopic examination.

MAIN OUTCOME MEASURES

The presence of myringosclerotic plaques, plaque dimensions and bilateral involvement of tympanic membranes were compared in the groups with and without atherosclerosis.

RESULTS

Amongst the 316 patients (75.0%) shown to have atherosclerosis, 65 (20.5%) also had myringosclerosis. Amongst the 105 patients without atherosclerosis, 24 (22.8%) had myringosclerosis. There was no statistically significant relationship between atherosclerosis and myringosclerosis (p > 0.05). Neither plaque dimensions nor bilateral involvement of the ears showed significant difference between the two groups (p >0.05 and p >0.05, respectively).

CONCLUSIONS

We conclude that there is no similar genetic tendency between atherosclerosis and myringosclerosis. The significance of the plaque dimensions and the bilateral involvement of tympanic membranes have not been satisfactorily discussed in the literature and this is the first time that they are being addressed. In contrast to the reported articles, there is no relationship between atherosclerosis and myringosclerosis other than being similar pathological processes occurring as a result of endothelial-epithelial damage.

Detection of osteoprotegerin and TNF-alpha mRNA in ankylotic Stapes footplates in connection with measles virus positivity

HYPOTHESIS

Otosclerosis is a bone remodeling disorder of the otic capsule causing conductive and sensorineural hearing loss. Persistent measles virus infection of the temporal bone with increased tumor necrosis factor (TNF)-alpha and decreased osteoprotegerin mRNA expression is supposed to be the main etiologic factor in otosclerosis.

BACKGROUND

Determinants of measles virus infection and reactive inflammation were studied in otosclerosis. The presence of measles virus was shown in otosclerotic patients by reverse transcriptase-polymerase chain reaction (RT-PCR) amplification of the viral RNA. No report is available, however, about the role and interactions of bone-specific cytokines in otosclerosis.

METHODS

: Nucleic acid was extracted from stapes footplates of clinically otosclerotic patients. Measles virus nucleoprotein RNA was amplified by seminested RT-PCR. TNF-alpha and osteoprotegerin mRNA coexpression was detected by RT-PCR in otosclerotic bone and was correlated to measles virus positivity.

RESULTS

Among 154 clinically stapes fixation otosclerotic patients, 99 stapedes contained measles virus RNA. TNF-alpha mRNA was detectable in 88 virus-positive and in 6 virus-negative stapes footplates. Osteoprotegerin mRNA expression was significantly lower in the TNF-alpha-positive specimens (P < .0001) that was independent from virus positivity.

CONCLUSION

Detection of TNF-alpha mRNA demonstrates activated osteoclast functions and inflammatory pathways in otosclerotic stapes footplates associated with measles virus presence. Increased expression of TNF-alpha and its action on RANK production inhibits the protective functions of osteoprotegerin on normal bone turnover in the otic capsule.

Glucocorticoids Inhibit Diastrophic Dysplasia Sulfate Transporter Activity in Otosclerosis by Interleukin-6

HYPOTHESIS/OBJECTIVE

Otosclerosis is a bone remodeling disorder localized to the otic capsule and associated with inflammation. In vitro, increased activity of the diastrophic dysplasia sulfate transporter (DTDST), which is implicated in bone metabolism, has been reported. Because glucocorticoids modulate the bone turnover and inhibit inflammatory processes, we investigated the effect of dexamethasone (Dex) on interleukin-6 and DTDST in otosclerosis.

STUDY DESIGN

The authors conducted a prospective, case-control study.

MATERIALS AND METHODS

Primary cell cultures were obtained from stapes and external auditory canals in otosclerosis (n = 21) and control patients (n = 18). Assays with [H]Dex evaluated specific binding sites in otosclerotic and control stapes. The effects of Dex (10 to 10 M) and RU486 (10 M), a glucocorticoid antagonist, were studied on DTDST activity by sulfate uptake. IL-6 secretion was measured in culture media before and after Dex (10 M, 24 hours). The effect of IL-6 (10 M, 24 hours) was assessed on DTDST activity in control stapes.

RESULTS

: The number of specific Dex-binding sites was similar in all stapedial cultures. Dex inhibited DTDST activity (19.4 +/- 1.02 vs. 29.4 +/- 3.94 pmol/microg prot/5 minutes) only in otosclerotic stapes. This effect was dose-dependent, antagonized by RU 486 and only observed 24 hours after Dex exposure. Interleukin (IL)-6 stimulated DTDST activity in normal stapes, whereas Dex inhibited IL-6 production only in otosclerotic stapes.

CONCLUSION

Dex inhibits the DTDST activity, at least in part, through a reduction of IL-6 secretion only in otosclerotic cells. This effect is mediated through the glucocorticoid receptors and may lead to the reduction of bone turnover.

Codetection of measles virus and tumor necrosis factor-alpha mRNA in otosclerotic stapes footplates

HYPOTHESIS

Otosclerosis is a disease of unknown etiology causing conductive or sensorineural hearing loss. Persistent measles virus infection of the otic capsule is considered to be one of the etiologic factors in otosclerosis.

BACKGROUND

Determinants of measles virus infection and reactive inflammation were studied in otosclerosis. The presence of measles virus was shown in otosclerotic patients by reverse-transcription polymerase chain reaction (RT-PCR) amplification of the viral RNA. No report is available, however, on the types and features of paracrine cytokines in otosclerosis.

METHODS

Nucleic acid was extracted from stapes footplate samples of clinically otosclerotic patients. Measles virus nucleoprotein RNA was amplified by seminested RT-PCR. Tumor necrosis factor (TNF)-alpha mRNA expression was detected by RT-PCR in otosclerotic bone and was correlated with preoperative audiologic findings and measles virus positivity.

RESULTS

Among 154 clinically otosclerotic patients, 99 stapes footplate specimens contained measles virus RNA. TNF-alpha mRNA was detectable in 88 virus-positive and in 6 virus-negative stapes footplates. There was no detectable TNF-alpha mRNA expression in virus negative cases.

CONCLUSION

The etiologic role of measles virus in the pathogenesis of otosclerosis should be considered. Detection of TNF-alpha mRNA demonstrates activated osteoclast functions and inflammatory pathways in otosclerotic stapes footplates associated with measles virus presence. Virus-associated and virus-negative pathomechanisms of otosclerosis should be distinguished.

Effect of 17 beta-estradiol on diastrophic dysplasia sulfate transporter activity in otosclerotic bone cell cultures and SaOS-2 cells

OBJECTIVE

Diastrophic dysplasia sulfate transporter (DTDST) is involved in the regulation of bone turnover, and its activity in otosclerosis has been shown to be abnormally high. Taking into account the role of estrogens in the progression of otosclerosis, the possible effect of estrogens on DTDST was investigated in otosclerotic bone cell cultures and in SaOS-2, a human osteoblastic cell line.

MATERIAL AND METHODS

Primary bone cell cultures of stapes and external auditory canal (EAC) bone were obtained from 33 patients with otosclerosis and 18 control patients undergoing cerebellopontine angle tumor surgery. These cultures were assessed in parallel with SaOS-2 cells. Estrogen receptors (ERs) were detected using reverse transcriptase polymerase chain reaction. DTDST activity was assessed by sulfate uptake at baseline and after 24 h of incubation with 17 beta-estradiol at concentrations ranging from 10(-12) to 10(-6) M.

RESULTS

Stapes and EAC cultures predominantly expressed mRNA of ER alpha, while ER beta expression was predominant in SaOS-2 cells. In stapes and EAC cultures no modification of DTDST activity was observed with 10(-8) M 17 beta-estradiol. In SaOS-2 cells, DTDST activity was inhibited by 17 beta-estradiol (93.5+/-9.21 vs 83.6+/-8.83 pmol/mg protein/5 min, n=29; mean of differences=10.0+/-3.22, paired t-test, p<0.01).

CONCLUSION

DTDST activity is regulated by estrogens in SaOS-2 cells, but not in primary cell cultures from stapes and EAC. This difference in the regulation mechanisms may be related to the type of estrogen receptor expressed.

Increased Activity of the Diastrophic Dysplasia Sulfate Transporter in Otosclerosis and Its Inhibition by Sodium Fluoride

HYPOTHESIS

This study investigates the function of the diastrophic dysplasia sulfate transporter (DTDST) in otosclerotic bone and the effect on it of sodium fluoride (NaF).

BACKGROUND

Otosclerosis is a localized bone dystrophy with increased bone turnover. DTDST is implicated in the regulation of the bone turnover.

MATERIALS AND METHODS

Primary cultures of cells were obtained from the stapes and external auditory canal (EAC) of 26 patients with otosclerosis and from nine control patients. Sulfate uptake was quantified under basal conditions and with NaF. The NaF signaling pathways were investigated using forskolin and verapamil.

RESULTS

The relative initial rates of sulfate uptake and the apparent Vmax values were: otosclerotic stapes > EAC > control stapes = control EAC. The sulfate uptake by the otosclerotic stapes was correlated with the loss of sensorineural hearing. The amounts of DTDST mRNA (RNase protection assay) in the four subgroups did not differ. NaF (10(-6)M, 1 hr) inhibited sulfate uptake by the otosclerotic stapes and EAC cells but not by control samples.

CONCLUSION

The authors believe that whether the increased DTDST activity is a cause or an effect of otosclerosis, it appears to be a specific target for NaF treatment.

The effect of local administration of N-acetylcysteine in perforated rat tympanic membrane: an experimental study in myringosclerosis

Myringosclerosis (MyS) is a common sequela of acute and chronic otitis media and ventilation tube treatment of serous otitis media. We aimed to study the effect of topical administration of N -acetylcysteine (NAC) on MyS by assessment of otomicroscopic evaluation, lipid peroxidation and nitric oxide (NO) (nitrite/nitrate) levels in experimental myringotomized rat tympanic membrane. Thirty adult rats were used and the upper posterior quadrant of the tympanic membranes of rats was myringotomized. Thereafter, they were divided into four groups. Group I received no treatment, group II was treated with saline, groups III and IV were treated with topical NAC (0.1 ml of 6 and 12 mg ml(-1), respectively). The levels of nitrite/nitrate and malondialdehyde (MDA) were measured in serum samples. In the otomicroscopic evaluation, non-treated and saline treated ears (controls) showed extensive occurrence of myringosclerotic plaques. Groups III and IV showed fewer occurrences of sclerotic plaques. There was no significant difference between groups III and IV regarding the development of MyS. The development of myringosclerotic lesion was found to be significantly different between NAC treated groups (III and IV) and the control groups (I and II). The levels of nitrite/nitrate of both groups III and IV were significantly lower than the control groups. The levels of MDA of these groups were also significantly lower than the control group. The relationship between groups III and IV was not statistically significant for the levels of nitrite/nitrate and MDA. We conclude that the topical treatment of NAC reduces the levels of MDA and NO products in rats. These results suggest that topical NAC application may be useful for the prevention of MyS.

Scanning electron microscopy images and energy-dispersive X-ray microanalysis of the stapes in otosclerosis and Van der Hoeve syndrome

OBJECTIVE/HYPOTHESIS

The objective of this study was to evaluate the morphological and microchemical changes that affect sclerotic stapes in otospongiosis and van der Hoeve syndrome.

METHODS

A scanning electron microscope equipped with an energy-dispersive x-ray analyzer was used in the experiments.

RESULTS

In otosclerosis, focal lesions are poorly mineralized, with low calcium salt and reduced calcium-to-phosphorus (Ca/P) ratio (1.9:1). This finding correlates with a spongiotic type of lesion and indicates unstable mineralization with possible change from hydroxyapatite to calcium triphosphate. In van der Hoeve syndrome the presence of magnesium in stapes suggests osteoclastic function stimulation. The osteoclasts secrete many protons, causing an acidified microenvironment. Brushite is formed, and Ca/P ratio decreases in comparison with that of control patients (2.0:1 vs. 2.6:1).

Glycosaminoglycan metabolism and cytokine release in normal and otosclerotic human bone cells interleukin-1 treated

Glycosaminoglycans (GAGs), normal components of the extracellular matrix (ECM), and the glycosidases, that degrade them, play a key role in the bone remodelling process. The effects of interleukin-1 alpha (IL-1 alpha) on GAG metabolism in normal and otosclerotic human bone cells as well as its capacity to modulate IL-1 alpha, IL-1 beta and IL-6 secretion in both populations was analyzed. The amount of radiolabeled GAGs was lower in otosclerotic than in normal bone cells. IL-1 alpha reduced newly synthesized cellular and extracellular GAGs in normal cells, but only those of the cellular compartment in otosclerotic bone cells. It depressed heparan sulphate (HS) more in normal cells and chondroitin sulphate (CS) more in otosclerotic bone cells. The HA/total sulphated GAG ratio was shifted in favour of the latter in otosclerotic cells, whereas the opposite effect was seen after IL-1 alpha treatment. There was little difference in the beta-D-glucuronidase levels of the normal and pathological cells, while beta-N-acetyl-D-glucosaminidase was significantly increased in otosclerotic bone cells. As the activity of neither enzyme was modified by treatment with IL-1 alpha, the cytokine seems to exert its influences on GAG synthesis rather than on the degradation process. IL-1 alpha, IL-1 beta and IL-6 secretion was markedly higher in otosclerotic cells. IL-1 alpha modulated the secretion of each interleukin differently, thus resulting in a cytokine cascade that may act in autocrine/paracrine manner on target cells. The authors suggest that changes in the cytokine network may have a specific, yet still unknown, role during normal and pathological osteogenesis.

Human otosclerotic bone-derived peptide decreases the gain of the electromotility in isolated outer hair cells

An otosclerotic peptide (OP) (Sziklai et al., 1985a.b) was purified from perilymph and stapes footplate of otosclerotic patients by Sephadex G-25 gel column chromatography and subsequent isotachophoretic (ITP) separation. The transfer function of the electromotility was measured by inserting the isolated outer hair cells (OHC) into a partitioning microchamber (Evans et al., 1991) and applying a series of pairs of brief square-pulse stimuli with opposite polarity and with increasing magnitude. Somatic length changes of the inserted part of the OHCs were measured by an optoelectronic system. The isotachophoretically homogeneous peptide exerted a gain and magnitude decreasing effect on the transfer function of electromotility of isolated OHCs of the guinea pig, in vitro. The operating point of the electromotility did not change due to the effect of the peptide. The peptide decreased the electromotile performance within a minute and bath exchange to normal saline did not completely restore the transfer curve to baseline. Application of caffeine to the cells already under the effect of the otosclerotic peptide produced an opposite effect: gain and magnitude increase. Simultaneous application of acetylcholine (ACh) did not antagonize the effect of OP. The underlying mechanism of the action of OP on the transfer function of electromotility of OHCs is postulated to involve the modulation of intracellular Ca2- concentration.

Phenotype of in vitro human otosclerotic cells and its modulation by TGF beta

A study was carried out to obtain a more detailed picture of the phenotypes of human otosclerotic and normal bone cells and to analyse the response of both populations to treatment with TGF beta 1. Total collagen synthesis was found to be decreased, but fibronectin secretion increased in otosclerotic with respect to normal cells. Although overall glycosaminoglycan (GAG) synthesis was lower in otosclerotic cells, the sulphated GAG to hyaluronic acid (HA) ratio was higher, in particular there was greater expression of chondroitin (CS) and dermatan sulphates (DS). TGF beta 1 induced a more marked increase in collagen and fibronectin release and greater production of sulphated GAGs as DS and heparan sulphate (HS) in the otosclerotic cells. The fact that the phenotype of the otosclerotic cells differed from that of the normal cells and could be modified by TGF beta 1 treatment, suggests that TGF beta 1 is implicated in the pathogenesis of otosclerosis.

Menière's syndrome: an approach to therapy

There are patients with symptoms similar to those of Menière's disease who do not have Menière's disease and therefore do not respond to conventional medical or conservative surgical management. Some have subtle disorders of carbohydrate and lipid metabolism and inner ear otosclerosis, which are responsible for the production of their symptoms. The response to dietary therapy confirms that glucose tolerance levels which are not diabetic nor hypoglycemic may be sufficiently significant in relation to inner ear function to produce the symptoms like those of Menière's Disease. Management of inner ear otosclerosis with supplemental sodium fluoride, calcium carbonate, and Vitamin D was also effective in controlling the symptoms in some patients.

Group specific component in serum and otosclerosis: no association

An earlier Swedish study suggested a positive association between otosclerosis and the group-specific component GC*1F marker. We investigated the distribution of GC subtypes in 101 Danish patients with otosclerosis who all had surgery performed in the county of Funen. Compared to 1674 Danish controls we found no evidence of any association between markers from the GC serum protein system and otosclerosis.

PTH induces modification of transductive events in otosclerotic bone cell cultures

We studied the effect of PTH (10-100 nM) on transductive mechanisms (adenylate cyclase activity, Ca2+ metabolism, IP3 levels) in cell cultures derived from normal and otosclerotic human bone fragments. The cultured cells were osteoblast-like but with calcitonin-receptors still present and with PTH receptors coupled with the adenylate cyclase system. The results showed that PTH activated adenylate cyclase and increased the intracellular Ca2+ levels with qualitative and quantitative differences between the two cellular populations. In particular, otosclerotic cells responded less to hormone stimulation, which is in accord with the current hypothesis of a desensitization of the receptor/enzyme complex associated with the pathological status.

Fine structure of the tendon of the human stapedius muscle: comparison of normals and clinically otosclerotic patients

The tendon of the human stapedius muscle was studied in normal post mortem material and in clinical otosclerotic patients, using light and electron microscopy. Cross section profiles of collagen fibrils were measured in various regions of the tendon and the amount of elastin was estimated. The normal stapedius tendon consisted of three concentrically arranged portions: A cylindrical central part, a tube-like mid-portion, and a cortical layer. The central part was made up of collagen fibrils with only a few elastic fibers, the mid-portion contained collagen fibrils together with significantly more elastic material, while the cortical layer, again, showed a smaller amount of elastic fibers. Mean diameters of collagen fibrils in the central part of the tendon were 65.12 +/- 11.89 nm, in the intermediate layer 41.00 +/- 9.63 nm, and in the cortical layer 70.28 +/- 19.58 nm. Stapedius tendons from clinically otosclerotic patients, though showing the same construction, were characterized by significantly altered collagen fibrillar diameters (Mann-Whitney U-test). In the central part, mean diameters were reduced to 61.05 +/- 14.70 nm, in the mid-portion increased to 50.90 +/- 10.08 nm, and in the cortical layer reduced to 61.09 +/- 8.49 nm. The changes of collagen cross section profiles estimated for the entire tendon were significant as well: 59.68 +/- 18.74 nm in controls versus 57.82 +/- 12.53 nm in otosclerotic patients. Elastin content in the mid-portion of control stapedius tendons increased with age (13% at 35 years of age to 35% at 70 years of age).(ABSTRACT TRUNCATED AT 250 WORDS)

Composition of the otosclerotic stapes: electron microprobe analyses

For the first time, otosclerotic stapes have been distinguished from unafflicted controls at a high level of significance by using a spectrum of elements measured by energy-dispersive spectrometer-electron probe microanalyses (EDS/EPMA). Discriminant analyses of the maximum concentration of 13 elements measured at several sites within each of 32 stapes differentiated otosclerotic from unafflicted individuals well above the 95% confidence level. Eight of the 9 control (unafflicted) and 21 of the 23 afflicted stapes were correctly classified. In descending order of contribution to the discriminant function, the elements are Zn > Cr > K > Ca > Si > Mn > Na > Al > Mg > P > Fe > S > Ti. Zinc and chromium account for much of the difference, but discriminant analyses excluding them still distinguish the two groups at the 95% confidence level. These results are consistent with previous reports of high levels of alkaline phosphatase, a zinc-containing enzyme, in afflicted stapes. But the broad spectrum of elements capable of distinguishing otosclerotic stapes warrants study of additional zinc-containing and other metal-containing or metal-activated moieties.

Inner ear basic fibroblast growth factor in CBA/J, C3H/HeJ, and autoimmune Palmerston north mice

Basic fibroblast growth factor (bFGF) has a mitogenic effect on fibroblasts and osteoblasts for matrix proliferation and on endothelial cells for neovascularization. Because otic capsule osteogenesis in autoimmune disease subjects often involves abnormal matrix and vascular changes, bFGF may serve as a potential mediator for such bone disorders. To investigate this relationship, bFGF was evaluated in the Palmerston North autoimmune strain mouse, which develops otic capsule sclerotic lesions during the progression of its systemic disease. Inner ears from PN mice, along with control CBA/J and C3H/HeJ mice, were immunohistochemically stained with antibodies against bFGF to identify its presence and possible role in otic capsule disease. Although cells reactive for bFGF were observed along the lining of the otic capsule in all three strains, a significantly higher frequency was observed in the PN mice. Other sites of staining included connective tissue around the tensor tympani muscle and the geniculate ganglion. This identification of bFGF in the otic capsule raises the possibility that it may play some role in normal bone maintenance, as well as abnormal bone or connective tissue remodeling in autoimmune disease.

Synthesis and secretion of glycosaminoglycans and proteins in human normal and otosclerotic bone cells

Some biosynthetic activities of normal and otosclerotic temporal bone cultures have been studied. Bone cells were cultured for 24 hrs. in medium containing 3H-glucosamine, 35SO4 or 3H-proline. Labelled glycosaminoglycans (GAG) and proteins were precipitated from cells and media. In otosclerotic bone cells there was an evident reduction in the synthesis and secretion of radiolabelled macromolecules. The inhibitory effect was always greater in the extracellular than in the intracellular compartment. Some glycosidases were also studied. Otosclerosis decreased the activity of all enzymes examined, indicating that the lower GAG synthesis and secretion in otosclerotic bone cells were not due to an increased degradation.

Characterization of the cytoskeleton in human normal and otosclerotic osteoblast-like cells

The localization and distribution of some cytoskeletal protein components were studied by immunostaining methods in normal and ostosclerotic osteoblast-like cells. The protein components investigated were microtubules (beta-tubulin), intermediate filaments (vimentin), microfilaments (actin and myosin) and structural proteins (alpha-actinin and fibronectin). Although the mechanism is not yet clear, the alterations observed in the pathological cells could well play a role in the expression of otosclerosis.

Type II collagen distribution in the monkey ear

A possible role for type II collagen autoimmunity in the pathogenesis of Meniere's disease and otosclerosis was recently suggested by studies demonstrating anti-type II collagen antibody in the serum of humans with these disorders and by the induction of similar lesions in animals immunized with type II collagen. In light of these findings, we studied the anatomic distribution of type II collagen in the nonhuman primate ear by immunohistochemical techniques using defined monoclonal antibodies to type II collagen. Type II collagen was observed in the cartilage plate of the auricle and external auditory meatus, tympanic annulus, lamina propria of tympanic membrane (pars tensa), interossicular joints, stapes footplate, eustachian tube cartilage, enchondral layer and globuli interossei of the otic capsule, Rosenthal canal, cribriform base, osseous spiral lamina, spiral ligament, limbus, tectorial membrane, semicircular canal membrane and subepithelial layer of the ampullary crista, utricular and saccular maculae, and the endolymphatic duct and proximal part of the sac. Thus, type II collagen should be considered an important component of ear tissue.

Hormonal receptor site alterations in the etiopathogenesis of otosclerosis

The authors have studied calcium 45 uptake and cAMP intracellular levels in normal and otosclerotic bone cell cultures after stimulation with calcitonin in the presence or absence of propranolol. The results seem to demonstrate that poststimulatory 45Ca incorporation is slightly different in normal and otosclerotic cell cultures, being slower but longer lasting in the latter. Propranolol administration markedly inhibits 45Ca uptake in normal cells, while in otosclerotic cells a massive intracellular penetration becomes evident after an initial inhibitory phase. Also cAMP intracellular levels behave differently; a marked increase, followed by a rapid decrease, can be detected in normal cells after stimulation with calcitonin, while in otosclerotic cells, the increase is slower and followed by a long lasting reduction. Adding propranolol reduces cAMP levels in normal cells, while it increases levels in otosclerotic cells. The different behavior of calcium metabolism and cAMP levels after stimulation with calcitonin, depending upon the presence or absence of propranolol, seems to indicate an alteration of the transducing mechanism between stimulus, receptor, and cellular effector in otosclerotic cells.

Possible role of peptides derived from otosclerotic bone in the mechanism of sensorineural hearing loss

Otosclerotic stapes footplates, superstructures and temporal cortical bones were extracted with 0.25 M guanidine X HCl 0.5 M EDTA (pH 7.4) solution. The extracted non-collagenous peptides/proteins were separated chromatographically on a Sephadex G-25 microcolumn. The peptide composition of the bone samples were compared by capillary analytical isotachophoresis (ITP) in the molecular mass range 0.3-5 kD. The otosclerotic stapes footplate contained 13 ITP subfractions, while the stapes superstructures and cortical bone contained only 9 and 10, respectively. An otosclerosis-specific ITP subfraction was also detected in the stapes footplate, but not in the stapes superstructure or cortical bone. This subfraction was previously demonstrated in the otosclerotic perilymph as well. Four ITP subfractions occurred common in the otosclerotic stapes footplate, the superstructure and the cortical bone. Two of these common subfractions were not found in the cortical bone peptide extract, but all of them revealed higher than normal levels in the otosclerotic perilymph.

The effect of flavone treatment on human otosclerotic ossicle organ cultures

We studied the effect of 7-isopropoxy-isoflavone (Ipriflavone) on the collagen synthesizing activity in human otosclerotic auditory ossicle samples from whole organ cultures during incubation for 96 h, and compared this effect with that found in normal meatal cortical bone. Ipriflavone led to a dose-dependent increase in the collagen synthesizing activity in both the healthy and the otosclerotic bone samples. At the highest Ipriflavone concentration used (50 microM), collagen synthesis increased 6-fold in the cortical bone and 9-fold in the otosclerotic bone, as compared with untreated controls. These findings indicate that the otosclerotic bone cavities are filled in vitro with organic matrix.

Cyclic nucleotide and prostaglandin F2 alpha contents of otosclerotic auditory ossicles

We found that the cyclic-adenosine-3',5'-monophosphate (cAMP) contents of otosclerotic human ossicles were 40-50 times greater than basal levels. Cyclic-guanosine-3',5'-monophosphate (cGMP) levels were also found to be greater than in physiological conditions, but lower than in cortical bone. These findings suggest the extensive participation of these nucleotide coenzymes in effector cells during the process of bone resorption. This emphasizes the role of bone-resorbing cells in this process as well as the probable osteoclast progenitor role of vascular endothelial cells and their enhanced activity for differentiation. At the same time, the absence of prostaglandin F2 alpha content in the otosclerotic bone analyzed appears to exclude cartilage remnants as a source for inducing the changes in remodelling that occur.

Vitamin D deficiency and otosclerosis

A prospective study of 47 patients with otosclerosis was undertaken to investigate the possible etiologic role of vitamin D undernutrition. The population comprised 27 women and 20 men, with a mean age of 46.4 years (range 21 to 79). The disease was bilateral in 43 patients, and cochlear involvement was present in 84.4%. The mean duration of symptoms was 17.1 years. Vitamin D status was evaluated by measuring the plasma 25-hydroxy vitamin D3 (25-OHD), which is the main storage metabolite. Abnormally low 25-OHD levels were found in 10 patients (21.7%) and borderline low levels in another two. Raised serum alkaline phosphatase levels were present in 32.6%, calcium in 6.5%, and inorganic phosphate in 4.3%. Calcium and vitamin D replacement therapy resulted in significant hearing improvement in 3 of 16 patients; these data support a causal correlation. Vitamin D deficiency is probably a factor in the etiology of some cases of otosclerosis and is important, since the deafness resulting from cochlear involvement may be reversible.

Non-collagen proteins of stapedial bone matrix in perilymph of otosclerotic patients

Non-collagen proteins extracted from the otosclerotic stapes footplate, superstructure and temporal cortical bone were compared with the protein patterns of normal and otosclerotic perilymph by analytical isotachophoresis (ITP). Normal and otosclerotic perilymph yielded basically identical isotachophoretic subfractions. Thirteen subfractions were detected moving as anions at pH 9.6 in the normal perilymph, versus 16 subfractions of similar character in the otosclerotic perilymph. Of these 16 protein subfractions, one (which was not detected in the normal perilymph) could be found in the ITP-gram of the stapes footplate non-collagen proteins, but not of the stapes superstructure or temporal cortical bone. Our results support the concept that protein can enter the inner ear fluid spaces from the otosclerotic bone. The biological significance of these proteins has not yet been clarified.

Peptides of the otosclerotic perilymph examined by analytical isotachophoresis

Perilymphs of normal and otosclerotic origin were separated chromatographically on a Sephadex G-25 microcolumn. Peptide composition of the perilymphs was compared by capillary analytical isotachophoresis in the molecular mass range 0.3-5 kD. Otosclerotic perilymph samples contain a heterogeneous, UV-absorbing peptide subfraction which is not detected in the normal perilymph. Normal and otosclerotic perilymph, furthermore, contain four common subfractions detected in twice the normal concentration in the otosclerotic perilymph. These ITP subfractions are degraded during acid hydrolysis (6 M HCI). On the contrary, otosclerosis is a deficient state compared with the normal, as the number of peptides or oligoglycopeptides is twice as high in normal as in otosclerotic perilymph, beside the otosclerosis specific peptides.

Collagen fibres in otosclerosis and in osteogenesis imperfecta tarda. A light and electron microscopic study

Skin biopsies taken from patients with osteogenesis imperfecta tarda and otosclerosis were compared blind by light- and electron microscopy with similar biopsies taken from normal volunteers in an effort to find common pathological features in the collagen fibres from the two patient groups, thus corroborating the theory that osteogenesis imperfecta and otosclerosis might be due to a common genetic anomaly in the form of a mesenchymal hypoplasia. We were not able to find differences in structure or quantity of the collagen-, elastic- or reticular fibres between normals and the two patient groups. We cannot, on the basis of our previous work and on the present morphological investigation, give support to the above-mentioned theory.

Otosclerosis and otospongiosis: clinical and histological comparisons

The simultaneous occurrence of otosclerosis and otospongiosis in the same lesion is well documented. The logical sequence of events would seem to be softening and destruction of the bone by the otospongiotic lesion, which is subsequently converted to otosclerosis. Examination of 46 temporal bones has led us to further classify the lesion as: 1. an active lesion, both otospongiotic and otosclerotic, 2. an inactive lesion, also both otosclerotic and otospongiotic, or 3. a fibrous lesion. Hyalinization of the spiral ligament only occurs adjacent to active otospongiotic or very large otosclerotic lesions. If the lesion adjacent to the spiral ligament is inactive, there is no hyalinization. It seems illogical that a hyalinized spiral ligament will return to normal when the lesion changes from active otospongiosis to inactive otosclerosis. Otospongiotic and otosclerotic lesions are found side by side at the periphery of lesions, and both are adjacent to normal bone. These findings have implications concerning the mode of action of sodium fluoride and other medications that are under evaluation for the control of the sensorineural hearing loss due to otosclerosis.

Histomorphometric analysis of iliac trabecular bone in otosclerosis

With the aim of investigating whether patients with otosclerosis suffer from a generalized bone disorder, a histomorphometric analysis of trabecular bone from the iliac crest was performed. Iliac crest biopsies from 10 patients with otosclerosis and 20 normal controls were obtained after tetracycline double labelling and examined by histomorphometry. No significant differences were found in the estimates of density and remodeling of bone between patients and sex and age-matched normal controls. Qualitatively the bone specimens showed no signs of any generalized bone disorder.

Perilymph oxygenation in sudden and progressive sensorineural hearing loss

The perilymphatic oxygen tension of the vestibular perilymph of 34 patients with different inner ear losses were measured with the polarographic method before and after inhalation with carbogen. Two patterns of disturbed perilymphatic oxygenation were observed: 1) Characterized by low initial values of perilymphatic oxygenation and normal response to carbogen inhalation was present in sudden deafness and sudden cochleovestibular loss of inner ear function. 2) Characterized by normal initial values of perilymphatic oxygenation and a low response to carbogen, was found in presence of a slowly progressive sensorineural hearing loss. The significance of the obtained results in regard to the possible vascular pathology of the inner ear is discussed.

Otosclerosis: relationship of spiral ligament hyalinization to sensorineural hearing loss

The sensorineural component of a mixed hearing loss due to otosclerosis is generally accepted as due to the otosclerotic lesion. The existence of pure cochlear otosclerosis without stapes fixation has been questioned. However, we are documenting 7 such cases in a separate publication. Results of this study, which evaluates 46 temporal bones with clinical or cochlear otosclerosis, demonstrate that the degree of sensorineural loss is directly related to the amount of hyalinization of the spiral ligament. The hyalinization occurs adjacent to active otospongiotic lesions but not next to inactive otosclerotic lesions. Both types of lesions may involve the cochlear endosteum. Small channels through the endosteal bone from the lesion to the spiral ligament have been found. The hyalinization spreads laterally from these channels. The hyalinization is presumably a result of the passage of toxic substances (proteolytic enzymes) from the lesion to the ligament. Strial atrophy is most pronounced on ligaments with the greatest degree of hyalinization. Hyalinization in only one ear produces decreased hearing compared to the other ear.

Examination of noncollagen protein composition of the footplate and superstructure of the otosclerotic stapes

We have differentially precipitated 2 fractions of noncollagen proteins extracted from separately pooled superstructure and footplate of surgically removed stapes of patients from both sexes, who have suffered from otosclerosis. The two fractions were: EDTA-soluble, CaCl2 precipitable (Fraction-1) and EDTA-soluble, CaCl2 non-precipitable proteins. The protein pattern of these two fractions was compared by isoelectric focusing and two-dimensional gel electrophoresis. The phosphoprotein fraction (Fraction-1) of the otosclerotic stapes footplate contained acidic (pI 3-6), low molecular weight (20-40 kD) proteins, which were not detected in the superstructure and temporal cortical bone. Two-dimensional mapping of the Fraction-2 showed predominantly acidic proteins in the footplate and some basic minor components in the superstructure. The lack of the low molecular weight proteins in the superstructure proves the localisation of the otosclerotic process only in the footplate.

Fragile bones and fragile ears

Conductive, sensorineural and mixed hearing loss occur in osteogenesis imperfecta in autosomal dominant inheritance pattern. Hearing loss is generally due to the middle and inner ear pathology of osteogenesis imperfecta and only occasionally to the coincidental association of otosclerosis and osteogenesis imperfecta. Two lesions cause the conductive hearing loss of osteogenesis imperfecta: (1) functional ossicular discontinuity due either to stapes superstructure fracture or fibrous replacement, or (2) thick, crumbly, lightly fixed stapes footplate. Cochlear hair cell loss, stria vascularis atrophy and calcification, tectorial membrane distortion and perilymph hemorrhage are autopsy findings that could account for sensorineural hearing loss, which occurs in a surprisingly high percentage of osteogenesis imperfecta patients. Hearing loss occurs earlier in osteogenesis imperfecta than in otosclerosis. Distinctive acoustic impedance and X-ray abnormalities occur in osteogenesis imperfecta. Other otologic findings may include lopped pinna, notching of the helix of the pinna, rosy flush of the medial wall of the middle ear and vestibular abnormalities.

Mineral content of skeletal bones in otosclerosis

In 63 patients with otosclerosis confirmed by operation, the bone mineral content was determined by photon absorptiometry. The bone mineral content and bone mineral concentration were found to be normal, which lends support to the assumption that otosclerosis is a localized disease and not a manifestation of a generalized disorder of the skeletal system.

Bone mineral content in osteogenesis imperfecta tarda and in otosclerosis

In 22 patients with osteogenesis imperfecta and in 63 patients with otosclerosis the bone mineral content in peripheral bones was determined by photon absorptiometry. The bone mineral content proved significantly reduced in patients with osteogenesis imperfecta as compared with normals and with patients with otosclerosis. In the latter patients the bone mineral content was normal. These findings support the assumption that stapedial fixation in otosclerosis and in osteogenesis imperfecta is of different aetiology.