Abstract
Conclusion: In spite of its absence in the control population, there is questionable evidence for the alteration c.114C->T in the HMX3 gene being implicated in the development of superior semicircular canal dehiscence (SSCD). However, the concept of a complex disease is valid for SSCD and a possible molecular origin can neither be confirmed nor excluded by the results of this study. Objectives: SSCD was first described in 1998 by Minor et al. While the etiology is not clear, findings from both temporal bone CT and histologic studies suggest a congenital or developmental origin. In recent years, a couple of genes regulating inner ear morphogenesis have been described. Specifically, Netrin-1 and HMX3 have been shown to be critically involved in the formation of the SCC. Molecular alterations in these two genes might lead to a disturbed development of this canal and might represent an explanation for SSCD. Methods: DNA was extracted from whole blood of 15 patients with SSCD. The coding sequences of Netrin-1 and HMX3 were amplified by PCR and sequenced. Results: One sequence alteration, heterozygous c.114C->T (conservative change without alteration of amino acid) in exon 1 of HMX3, was detected in 2 of 15 patients but not in 300 control chromosomes. The study was supported in part by the Emilia-Guggenheim-Schnurr-Foundation, Basel, Switzerland.
Highlights
The syndrome of superior semicircular canal dehiscence (SSCD) was identified by Minor et al in 1998 [1]
The dehiscence of a variable extent of the bone overlying the SCC has been demonstrated by highresolution computed tomography (HRCT) of the temporal bones in axial and coronal planes with 0.5 mm collimation with a sensitivity of 100% and a specificity of 99% [2,3]
A molecular-genetic defect might be the cause for SSCD
Summary
The syndrome of superior semicircular canal dehiscence (SSCD) was identified by Minor et al in 1998 [1]. Additional confirmation of the dehiscence stems from intraoperative findings and from a temporal bone study [3,4]. Findings from both the CT and histological study point to a congenital or developmental origin [2,4]. Two genes, HMX3 (Nkx5-1) and Netrin-1, which are critically involved in the formation of the SCC, have been published [5,6]. Both genes are expressed in the non-sensory vestibular epithelium. Additional evidence for Netrin-1 activity in tissue morphogenesis stems from the report of its role in the development of the mammary gland terminal end buds [7]
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