Gustatory lacrimation in association with the branchio-oto-renal syndrome

Anatomical Changes and Audiological Profile in Branchio-oto-renal Syndrome: A Literature Review

Introduction Branchio-oto-renal (BOR) syndrome is an autosomal-dominant genetic condition with high penetrance and variable expressivity, with an estimated prevalence of 1 in 40,000. Approximately 40% of the patients with the syndrome have mutations in the gene EYA1, located at chromosomal region 8q13.3, and 5% have mutations in the gene SIX5 in chromosome region 19q13. The phenotype of this syndrome is characterized by preauricular fistulas; structural malformations of the external, middle, and inner ears; branchial fistulas; renal disorders; cleft palate; and variable type and degree of hearing loss.

Aim Hearing loss is part of BOR syndrome phenotype. The aim of this study was to present a literature review on the anatomical aspects and audiological profile of BOR syndrome.

Data Synthesis Thirty-four studies were selected for analysis. Some aspects when specifying the phenotype of BOR syndrome are controversial, especially those issues related to the audiological profile in which there was variability on auditory standard, hearing loss progression, and type and degree of the hearing loss. Mixed loss was the most common type of hearing loss among the studies; however, there was no consensus among studies regarding the degree of the hearing loss.

Branchio-oto-renal syndrome

Branchio-oto-renal syndrome, a phenotype consisting of hearing loss, auricular malformations, branchial arch remnants, and renal anomalies is now recognized as one of the more common forms of autosomal dominant syndromic hearing impairment. Three loci known to be associated with the BOR phenotype have been identified and two genes that act in a regulatory network have been cloned, EYA1 and SIX1. EYA1 and SIX1 are homologous to genes involved in Drosophila eye development, eyes absent gene (eya), and sine oculis (so), respectively. EYA1, a transcriptional co-activator has a conserved, 271-amino acid, C-terminal known as the Eya Domain (ED). SIX1 has two highly conserved domains; a homeodomain (HD) and a specific Six-domain (SD) whose products function as transcription factors with specific DNA-binding activity that are crucial for protein-protein interaction. To determine the molecular basis for the organ defects that occur in BOR syndrome, many studies have focused on the effects of mutations to EYA and effects of mutations of the EYA-SIX regulatory system. However, over 60% of BOR syndrome patients do not have known mutations in EYA1 and relatively little is known about mutations to SIX1. Further evaluation of SIX1 and its related target genes may provide a better understanding of the pathophysiology of BOR syndrome and offer greater clues to the disease mechanisms.

Genomewide search and genetic localization of a second gene associated with autosomal dominant branchio-oto-renal syndrome: clinical and genetic implications

Branchio-oto-renal (BOR) syndrome is characterized by ear malformations, cervical fistulas, hearing loss, and renal anomalies. It is an autosomal dominant disorder with variable clinical manifestations. The most common features of BOR syndrome are branchial, hearing, and renal anomalies. However, many affected subjects have been observed with branchial-cleft anomalies and hearing loss but without renal anomalies, a condition called "branchio-otic" (BO) syndrome. It is logical to question whether the BOR and BO syndromes are allelic or whether they represent distinct genetic entities. We identified a very large extended family whose members had branchial and hearing anomalies associated with commissural lip pits that segregated in an autosomal dominant fashion. Using a genomewide search strategy, we identified genetic linkage, with a maximum LOD score of 4.81 at recombination fraction 0, between the BO phenotype and polymorphic marker D1S2757 in the genetic region of chromosome 1q31. This is the first report of linkage for a second gene associated with BOR syndrome. The findings have important clinical implications and will provide insight into the genetic basis of BOR syndrome.

New' manifestations of BOR syndrome

Defined in 1975, branchio-oto-renal (BOR) syndrome is an autosomal dominant disorder consisting of branchial arch anomalies, hearing loss, and urinary tract malformations. It is the prototype of the non-chromosomal syndromes that have branchial arch anomalies as major clinical manifestations: BOR, branchio-otic (BO), branchio-otic-facial (BOF), and Townes-Brock syndromes. Subsequently, several clinical manifestations have expanded its phenotype. Retrospective analysis of 31020 families evaluated between January 2, 1982 and December 31, 1996 at the genetic clinics of the University of South Florida, showed seven probands with BOR/?BOR syndrome. Four of the probands and affected relatives had manifestations that further expanded the phenotype: gustatory lacrimation, hypospadias, imperforate anus, osteosclerosis, microcephaly, hypodontia, congenital vocal cord paresis, and congenital incomplete fixation of the transverse colon. Thus, BOR/ ?BOR syndrome appears to be a clinically and genetically heterogeneous multiorgan/system entity that manifests itself predominantly during organogenesis. Clinicians and researchers alike should be cognizant of the expanded phenotype and heterogeneity, while in the DNA laboratories the latter will be sorted out.

Congenital cholesteatoma and malformations of the facial nerve: rare manifestations of the BOR syndrome

We describe a 14-month-old girl with unilateral congenital cholesteatoma and anomalies of the facial nerve in addition to the more common branchial arch, otic, and renal malformations comprising the branchio-oto-renal (BOR) syndrome. Her mother also has the BOR syndrome and unilateral duplication of the facial nerve. This is the first study of a BOR patient with congenital cholesteatoma and the second family in which cholesteatoma and anomalies of the facial nerve are described in patients with the BO/BOR syndrome. We review the congenital cholesteatoma literature and discuss hypotheses for the pathogenesis of this entity in light of this new report.

Branchio-oto-renal syndrome: identification of novel mutations, molecular characterization, mutation distribution, and prospects for genetic testing

The branchio-oto-renal syndrome (BOR) is an autosomal dominant disorder characterized by branchial clefts, preauricular sinuses, hearing loss, and renal anomalies. The BOR gene, EYA1, on chromosome 8q13 has recently been cloned and mutations have been identified. In this study, we have analyzed the sites of mutations in the EYA1 gene in BOR patients to determine the spectrum of mutations. We have identified two missense mutations and have compared all the mutations reported to date in the EYA1 gene. In total, 20 mutations have been described, the majority of which are clustered in the carboxy-terminal region of the gene. The clinical features of the BOR individuals have also been compared to determine if the nature of the mutation correlates with the type and severity of the clinical symptoms. Most of the mutations arose de novo and, other than the clustering in carboxy-terminal exons 9-16, no mutation hot spots have been identified. These results provide the basis for molecular genetic testing that will help in the clinical evaluation and genetic counseling of members of BOR families.

Eya1 expression in the developing ear and kidney: towards the understanding of the pathogenesis of Branchio-Oto-Renal (BOR) syndrome

Branchio-Oto-Renal (BOR) syndrome is an autosomal dominant, early developmental defect characterised by varying combinations of branchial (fistulas, sinuses, and cysts), outer, middle and inner ear, and renal anomalies. The gene underlying this syndrome, EYA1, is homologous to the Drosophila developmental gene eyes absent which encodes a transcriptional co-activator required for eye specification. We report here the temporal and spatial pattern of expression of the murine homologue, Eya1, throughout ear and kidney development in relation to the anomalies of BOR syndrome. The expression of Eya1 in the branchial arch apparatus (namely in the 2nd, 3rd, and 4th branchial clefts and pharyngeal pouches) at embryonic day (E)10.5, can be correlated with the branchial fistulas, sinuses, and cysts but not with the outer and middle ear anomalies. In contrast, Eya1 is expressed during the slightly more advanced stage of outer and middle ear morphogenesis at E13.5, in the mesenchyme adjacent to the first branchial cleft (the cleft will give rise to the external auditory canal and the surrounding mesenchyme to the auricular hillocks) and surrounding the primordia of the middle ear ossicles, and in the epithelium of the tubotympanic recess (the future tympanic cavity). During early inner ear development, Eya1 is expressed in the ventromedial wall of the otic vesicle (the site of the future sensory epithelia), in the statoacoustic ganglion, and in the periotic mesenchyme, consistent with the cochlear anomalies and sensorineural hearing loss of BOR syndrome. Subsequently, Eya1 expression is observed in the differentiating hair and supporting cells of the sensory epithelia, as well as in the associated ganglia, and persists after differentiation has taken place. This suggests that, in addition to a role in the morphogenetic process, Eya1 could also be implicated in the differentiation and/or survival of these inner ear cell populations. Finally, Eya1 expression in the condensing mesenchymal cells of the kidney is consistent with the excretory and collecting system anomalies of BOR syndrome. From the comparison of the Eya1 and Pax2 expression patterns during ear and kidney development, a contribution of these two genes to the same regulatory pathway can only be suggested in the mesenchymal-epithelial transition directing renal tubule formation.

Branchio-oto-renal (BOR) syndrome: variable expressivity in a five-generation pedigree

A five-generation family with the branchio-oto-renal (BOR) syndrome is reported demonstrating the great variability of this syndrome. Symptoms of the branchio-oto, branchio-oto-ureteral, and BOR syndromes are seen in different members of this family, suggesting that these are not real entities, but variants of the BOR syndrome.