Inner ear anomalies in Waardenburg's syndrome associated with Hirschsprung's disease

Cochlear histopathology in human genetic hearing loss: State of the science and future prospects

Sensorineural hearing loss (SNHL) is an extraordinarily common disability, affecting 466 million people across the globe. Half of these incidents are attributed to genetic mutations that disrupt the structure and function of the cochlea. The human cochlea's interior cannot be imaged or biopsied without damaging hearing; thus, everything known about the morphologic correlates of hereditary human deafness comes from histopathologic studies conducted in either cadaveric human temporal bone specimens or animal models of genetic deafness. The purpose of the present review is to a) summarize the findings from all published histopathologic studies conducted in human temporal bones with known SNHL-causing genetic mutations, and b) compare the reported phenotypes of human vs. mouse SNHL caused by the same genetic mutation. The fact that human temporal bone histopathologic analysis has been reported for only 22 of the nearly 200 identified deafness-causing genes suggests a great need for alternative and improved techniques for studying human hereditary deafness; in light of this, the present review concludes with a summary of promising future directions, specifically in the fields of high resolution cochlear imaging, intracochlear fluid biopsy, and gene therapy.

Spectrum of temporal bone abnormalities in patients with Waardenburg syndrome and SOX10 mutations

BACKGROUND AND PURPOSE

Waardenburg syndrome, characterized by deafness and pigmentation abnormalities, is clinically and genetically heterogeneous, consisting of 4 distinct subtypes and involving several genes. SOX10 mutations have been found both in types 2 and 4 Waardenburg syndrome and neurologic variants. The purpose of this study was to evaluate both the full spectrum and relative frequencies of inner ear malformations in these patients.

MATERIALS AND METHODS

Fifteen patients with Waardenburg syndrome and different SOX10 mutations were studied retrospectively. Imaging was performed between February 2000 and March 2010 for cochlear implant work-up, diagnosis of hearing loss, and/or evaluation of neurologic impairment. Eleven patients had both CT and MR imaging examinations, 3 had MR imaging only, and 1 had CT only.

RESULTS

Temporal bone abnormalities were bilateral. The most frequent pattern associated agenesis or hypoplasia of ≥1 semicircular canal, an enlarged vestibule, and a cochlea with a reduced size and occasionally an abnormal shape, but with normal partition in the 13/15 cases that could be analyzed. Three patients lacked a cochlear nerve, bilaterally in 2 patients. In addition, associated abnormalities were found when adequate MR imaging sequences were available: agenesis of the olfactory bulbs (7/8), hypoplastic or absent lacrimal glands (11/14), hypoplastic parotid glands (12/14), and white matter signal anomalies (7/13).

CONCLUSIONS

In the appropriate clinical context, bilateral agenesis or hypoplasia of the semicircular canals or both, associated with an enlarged vestibule and a cochlear deformity, strongly suggests a diagnosis of Waardenburg syndrome linked to a SOX10 mutation.

The rare phakomatoses

This article outlines the clinical, central nervous system, and neuropathologic features,pathogenesis, genetics, molecular biology, and neuroimaging characteristics of the rare vascular phakomatoses, melanophakomatoses, and organoid phakomatoses.

Temporal bone abnormalities associated with hearing loss in Waardenburg syndrome

OBJECTIVES/HYPOTHESIS

The objectives were to correlate audiometric thresholds with radiological findings and to determine the prevalence of inner ear radiological abnormalities in patients with hearing loss and Waardenburg syndrome.

STUDY DESIGN

The study was a retrospective review of patients with Waardenburg syndrome identified in a pediatric hearing-impaired population and human genetics clinic.

METHODS

Nine children with Waardenburg syndrome were identified. Eighty-nine children without sensorineural hearing loss served as control subjects. Clinical data, audiometric thresholds, and radiographic temporal bone measurements in these children were analyzed.

RESULTS

Seven children were identified with hearing loss and Waardenburg syndrome. Four children had Waardenburg syndrome type 1, and three children had Waardenburg syndrome type 2. The overall prevalence of hearing loss in the total study population with Waardenburg syndrome was 78%. The mean pure-tone average was 99 dB. All of the children had sensorineural hearing loss. The hearing outcome was stable in 86% of the children. Twelve temporal bones were available for radiological analysis by computed tomography. Enlargement of the vestibular aqueduct was found in 50% of the CT scans. There was a significant difference in measurements of vestibular aqueduct width at the midpoint between the patients with Waardenburg syndrome and the control group (P <.05). There were also significant differences in the measurements of the vestibule (P =.0484), internal auditory canal (P =.0092), and modiolus (P =.0045) between the children with Waardenburg syndrome and the control group.

CONCLUSION

A profound sensorineural hearing loss was characteristic of the study population with Waardenburg syndrome. Overall, 100% of patients with hearing loss and Waardenburg syndrome had temporal bone anomalies on at least one measurement of their inner ear, and 50% had an enlargement of the vestibular aqueduct at the midpoint. As shown by computed tomography, enlargement of the vestibular aqueduct and the upper vestibule, narrowing of the internal auditory canal porus, and hypoplasia of the modiolus are features of Waardenburg syndrome.

Vestibular abnormalities in congenital disorders

This paper reviews the histopathologic features of vestibular abnormalities in congenital disorders affecting the inner ear, based upon a comprehensive literature survey and a review of cases in our temporal bone collection. The review proceeds in three systematic steps. First, we surveyed associated diseases with the major phenotypic features of congenital abnormalities of the inner ear (including the internal auditory canal and otic capsule). Second, the vestibular anomalies are examined specifically. Finally, the anomalies are discussed from a developmental perspective. Among vestibular anomalies, a hypoplastic endolymphatic duct and sac are observed most frequently. Anomalies of the semicircular canals are also often observed. From embryological and clinical viewpoints, many of these resemble the structural features from fetal stages and appear to be associated with vestibular dysfunction. It is expected that progress in genetic analysis and accumulation of temporal bone specimens with vestibular abnormalities in congenital diseases will provide crucial information not only for pathology of those diseases, but also for genetic factors that are responsible for the specific vestibular abnormalities.

Otopathology in a case of type I Waardenburg's syndrome

We report a case of type I Waardenburg's syndrome that provides insight into the etiopathogenesis of sensorineural hearing loss (SNHL) in this syndrome. The subject, a 76-year-old woman with type I Waardenburg's syndrome (dystopia canthorum, heterochromia irides, and white hair), had congenital low-frequency SNHL in her right ear only, which had remained relatively stable throughout her life. Blood leukocyte DNA studies revealed a PAX-3 mutation with a 1 base pair C-to-A substitution in exon 5 at base 602. Light microscopic studies of the right cochlea showed intact neurosensory structures in only the lower basal turn, with the remainder of the cochlea showing absence of melanocytes, absence of stria vascularis, missing hair cells, dysmorphogenesis of the tectorial membrane, and lack of peripheral processes of the spiral ganglion cells. There was pathological alteration of the vestibular dark cells with marked reduction of melanocytes associated with these dark cells. The left inner ear was normal, with a full complement of neurosensory structures, including melanocytes. Because the PAX-3 gene is involved in neural crest development and melanocytes migrate from the neural crest to the ear, the findings in this case are consistent with the hypothesis that defective melanocyte migration or defective melanocyte function results in defective development of the stria vascularis (and perhaps other structures of the ear), leading to SNHL.

Temporal bone imaging findings in Waardenburg's syndrome

OBJECTIVE

(a) To report computed tomography findings of eight new cases with Waardenburg's syndrome (WS) type I and review reported temporal bone radiographic and histopathological findings in WS with hearing loss; (b) To determine the frequency of inner ear pathologies that may contraindicate cochlear implantation.

METHODS

A review of 1166 pediatric patients with sensorineural hearing loss revealed 12 cases (1%) with WS, whose family screenings disclosed additional 12 subjects with the same disorder. Among these 24 cases, eight had WS type I and were subjected to computed tomography scanning of temporal bone. Imaging findings of 28 cases reported previously in English literature were evaluated together with our eight patients.

RESULTS

Malformation of the inner ear was found in none of the nine WS type I cases evaluated here, while the frequency of internal acoustic canal malformation was 11%. Regardless of the subtypes of the syndrome, 6 of 36 cases (17%) had radiological abnormality of the inner ear. Malformation and/or absence of the semicircular canals were the most common congenital abnormality of the inner ear. Hypoplasia of the cochlea was present in 3 of 36 cases (8%).

CONCLUSIONS

Abnormality of bony labyrinth in WS with congenital deafness is not a frequent finding, particularly in WS type I. Therefore, the otologist and audiologist must keep in mind that most of these cases are suitable for cochlear implantation regarding inner ear anatomy.

An epidemiological study of Hirschsprung's disease and additional anomalies

The incidence of Hirschsprung's disease was studied in approximately 1.5 million consecutive live births in Denmark by hospital records. A diagnosis of Hirschsprung's disease required a histologic verified absence of ganglion cells in either biopsy or surgical colonic specimens. The incidence of Hirschsprung's disease was found to be 0.140 per 1000 live births (1:7,165) with a male: female ratio of 4.1:1 in short segment, and 2.4:1 in long segment Hirschsprung's disease (p = 0.36). Maternal age and birth order were unimportant factors. The association of Hirschsprung's disease and Down's syndrome was seen in 9 of the 207 patients and may represent a real association, whereas the association with congenital heart defects seen in 2% (not including patients with Down's syndrome) is more doubtful. A mortality of 16% among the patients with Hirschsprung's disease emphasizes the extreme importance of early diagnosis.

Contemporary approaches toward understanding the pathogenesis of Hirschsprung disease

Hirschsprung disease (HD), or congenital aganglionosis coli, is a birth defect with heterogeneous causes. In an effort to understand the molecular and cellular bases for this disorder, researchers have investigated enteric neurodevelopment in normal animals and compared these findings with observations of inbred animal strains that develop aganglionosis coli due to mutations at specific genetic loci. Recent technological advances, including use of retroviral and fluorescent lineage makers, immunohistochemical probes, and transgenic mice, have provided insights into the origins, behavior, and properties of enteric neuroblasts. Experiments with mutant murine embryos indicate that aganglionosis coli results from primary failure of neural crest-derived neuroblasts to colonize the distal colon. In at least one model, impaired colonization by neuroblasts may be secondary to environmental defects restricted to colonic mesenchyme. The discovery that human piebald trait, a hereditary disorder with a high incidence of HD, is caused by mutations in a growth factor receptor highlights the importance of regulatory intercellular interactions between nonneuroblastic mesenchyme and neuroblasts during normal development of the enteric nervous system. These observations, coupled with advances in molecular genetics, set the stage for dramatic progress in this field of research in the near future.

Normal hearing in Splotch (Sp/+), the mouse homologue of Waardenburg syndrome type 1

Splotch is considered a model of Waardenburg syndrome type I (WSI) because the abnormalities are caused by mutations in homologous genes, Pax-3 in mice and PAX3 (HuP2) in humans. We examined inner ear structure and function in Splotch mutants (Sp/+) and found no sign of auditory defects, in contrast to the deafness in many WSI individuals. The difference in expression of the genes in the two species may be due to different parts of the gene being mutated, or may result from variations in modifying influences as yet undefined.