Molecular Vision 2010; 16:650-664 <http://www.molvis.org/molvis/v16/a74> © 2010 Molecular Vision Received 15 July 2009 | Accepted 6 April 2010 | Published 13 April 2010 Nonsense mutation in TMEM126A causing autosomal recessive optic atrophy and auditory neuropathy Esther Meyer,1 Michel Michaelides,2,3 Louise J. Tee,1 Anthony G. Robson,2,3 Fatimah Rahman,1 Shanaz Pasha,1 Linda M. Luxon,4,5 Anthony T. Moore,2,3 Eamonn R. Maher1 1Department of Medical and Molecular Genetics, Institute of Biomedical Research, University of Birmingham, Birmingham, UK; 2UCL Institute of Ophthalmology, 11-43 Bath Street, London, UK; 3Moorfields Eye Hospital, City Road, London, UK; 4UCL Ear Institute, 332 Grays Inn Road, London, UK; 5Great Ormond Street Hospital for Children, Great Ormond Street, London, UK Purpose: To define the phenotype and elucidate the molecular basis for an autosomal recessively inherited optic atrophy and auditory neuropathy in a consanguineous family with two affected children. Methods: Family members underwent detailed ophthalmologic, electrophysiological, and audiological assessments. An autozygosity mapping strategy using high-density single nucleotide polymorphism microarrays and microsatellite markers was used to detect regions of genome homozygosity that might contain the disease gene. Candidate genes were then screened for mutations by direct sequencing. Results: Both affected subjects had poor vision from birth and complained of progressive visual loss over time. Current visual acuity ranged from 6/60 to 6/120. Fundus examination revealed bilateral temporal optic nerve pallor in both patients with otherwise normal retinal findings. International-standard full-field electroretinograms were normal in both individuals, with no evidence of generalized retinal dysfunction. Pattern cortical visual evoked potentials were grossly abnormal bilaterally in both cases. The pattern electroretinogram N95:P50 ratio was subnormal, and the P50 was of shortened peak time bilaterally in both patients. The electrophysiological findings were consistent with bilateral retinal ganglion cell/optic nerve dysfunction. Audiological investigation in both siblings revealed abnormalities falling within the auditory neuropathy/dysynchrony spectrum. There were no auditory symptoms and good outer hair cell function (as demonstrated by transient evoked otoacoustic emissions) but impaired inner hair cell/neural function with abnormal stapedial reflex thresholds and abnormal or absent auditory brainstem-evoked responses. The single nucleotide polymorphism microarray data demonstrated a 24.17 Mb region of homozygosity at 11q14.1–11q22.3, which was confirmed by microsatellite marker analysis. The candidate target region contained the transmembrane protein 126A (TMEM126A) gene, and direct sequencing identified a previously described nonsense mutation (c.163C>T; p.Arg55X). Conclusions: We describe the first detailed phenotyping of patients with autosomal recessive TMEM126A-associated optic atrophy and auditory neuropathy. These findings will facilitate the identification of individuals with this recently described disorder. Primary hereditary optic neuropathies comprise a group Recently, Hanein et al. [4] identified a second locus for of disorders that are characterized by visual loss due to retinal autosomal recessive optic atrophy on chromosome 11 and ganglion cell death. The most common forms of optic identified germline mutations in transmembrane protein 126A neuropathy are Leber hereditary optic neuropathy (LHON) gene (TMEM126A) in affected individuals from four families. with mitochondrial transmission (OMIM 535000) and Autosomal recessive auditory neuropathy has been autosomal dominant optic atrophy (OMIM 165500) [1]. reported in association with mitochondrial myopathy and Autosomal recessive optic neuropathies are uncommon and mitochondrial DNA multiple deletions [5], but commonly it are mostly observed in association with multisystem diseases. presents as congenital nonsyndromic hearing impairment as a A few cases of isolated autosomal recessive optic atrophy consequence of mutations in the otoferlin (OTOF) gene, a have been reported [2]. Previously Barbet et al. [3] mapped a membrane-anchored calcium-binding protein that plays a role locus for early onset but slowly progressive optic neuropathy in the exocytosis of synaptic vesicles at the auditory inner hair (OPA6; OMIM 258500) to chromosome 8q. Affected family cell ribbon synapses [6]. Nonsyndromic autosomal recessive members presented with visual impairment commencing auditory neuropathy has also been reported in association with between 2 and 6 years of age, moderate photophobia, and missense mutations in the autosomal recessive deafness 59 dyschromatopsia. There were no associated systemic features. gene on chromosome 2q31.1-q31.3, which encodes the protein pejvakin found in hair cell, supporting cells, spiral Correspondence to: Eamonn R. Maher, Department of Medical and ganglion cells, and the first three relays of the afferent auditory Molecular Genetics, Institute of Biomedical Research, University of pathway [7]. Birmingham, Birmingham, UK; Phone: +44 121 627 2741; FAX: +44 121 627 2618; email: [email protected] 650 Molecular Vision 2010;16:650-664 <http://www.molvis.org/molvis/v16/a74> TABLE 1. SUMMARY OF OPHTHALMOLOGICAL FINDINGS. Patient Sex Age Symptoms Presenting Current Refraction Fundus ERG PERG Pattern and flash visual acuity visual acuity VEPs OD-OS OD-OS IV:1 F 19 Reduced vision 3/36–3/36 (14y) 6/95–6/95 −0.75/-0.25x180 Bilateral Normal N95:P50 ratio is Severely abnormal since birth −0.75/-0.25x180 marked subnormal and pattern and flash temporal P50 is of short VEPs bilaterally. 651 optic nerve peak time pallor bilaterally IV:2 M 17 Reduced vision 6/60 – 6/60 (12y) 6/120–6/60 −0.75/-0.50x90 Bilateral Normal N95:P50 ratio is Severely abnormal since birth; plano/-0.50x15 temporal subnormal and pattern VEPs. Flash horizontal optic nerve P50 is of short VEPs within normal nystagmus; right pallor peak time limits. exotropia bilaterally Abbreviations: OD-OS represents: Oculus Dexter - Oculum Sinister; ERG represents Electroretinogram; PERG represents Pattern ERG; VEP represents Visual Evoked Potential; F represents Female; M represents Male; y represent Year. © 2010MolecularVision Molecular Vision 2010; 16:650-664 <http://www.molvis.org/molvis/v16/a74> © 2010 Molecular Vision Figure 1. Fundal appearance. Color fundus photographs of both eyes of the two affected siblings. Bilateral temporal optic disc pallor and normal retinal appearance (IV:1 above and IV:2 below) are seen. The co-occurrence of optic neuropathy and auditory a mutation in TMEM126A. Our findings suggest that auditory neuropathy is rare, but two cases of LHON with auditory neuropathy may be an additional previously unreported neuropathy have been reported [8], although a more recent feature of this disorder. study has documented that this is an uncommon finding in LHON [9]. The X-linked recessive deafness-dystonia-optic METHODS neuronopathy syndrome (Mohr-Tranebjaerg syndrome; Patients: A consanguineous family of Algerian origin with OMIM 304700) is characterized by postlingual sensorineural two affected children was ascertained and recruited for hearing loss in early childhood, with progressive neural clinical and molecular genetic studies. All subjects gave degeneration affecting the brain, eighth cranial nerve, and written informed consent. The study was approved by the optic nerves in adult life. The auditory findings indicate South Birmingham Local Research Ethics Committee and auditory neuropathy, with spiral ganglion cells being the was performed in accordance with the Declaration of suspected site of pathology. The X-linked recessive deafness- Helsinki. Genomic DNA from the two affected individuals, dystonia-optic neuronopathy is caused by mutations in the two unaffected siblings, and the parents were extracted from translocase of inner mitochondrial membrane 8 homolog A peripheral lymphocytes by standard techniques. (yeast) gene which is also called deafness/dystonia peptide gene and encodes for a 97 amino acid polypeptide [10]. Ocular assessment: Both affected siblings (IV:1 and IV:2) were examined. A medical and ophthalmic history was taken, We report the results of detailed clinical, and a full ophthalmologic examination was performed. Color electrophysiological, audiological, and molecular genetic vision was tested using Ishihara pseudoisochromatic plates investigations in a family with optic atrophy associated with and Hardy, Rand and Rittler plates (American Optical 652 Molecular Vision 2010; 16:650-664 <http://www.molvis.org/molvis/v16/a74> © 2010 Molecular Vision Figure 2. Retinal nerve fiber layer analysis. The results of this analysis demonstrates the marked global reduction in nerve fiber layer thickness compared to normative values (using the Zeiss Stratus® OCT 3) in Patient IV:1. Company, New York, NY). Each patient underwent color the Zeiss Stratus® OCT 3 (Carl Zeiss Meditec Inc., Dublin, fundus photography, Goldmann perimetry (Haag-Streit AG, CA). Both patients had detailed electrophysiological Bern, Switzerland), and retinal nerve fiber layer analysis using assessment, including a full-field electroretinogram (ERG) 653 Molecular Vision 2010; 16:650-664 <http://www.molvis.org/molvis/v16/a74> © 2010 Molecular Vision Figure 3. International-standard full-field electroretinogram of the two affected individuals of the optic atrophy family. This figure shows the electroretinogram (ERGs) from