Panel-based next-generation sequencing identifies novel mutations in Bulgarian patients with inherited retinal dystrophies.

BACKGROUND: Next-generation sequencing (NGS)-based method is being used broadly for genetic testing especially for clinically and genetically heterogeneous disorders, such as inherited retinal degenerations (IRDs) but still not routinely used for molecular diagnostics in Bulgaria. Consequently, the purpose of this study was to evaluate the effectiveness of a molecular diagnostic approach, based on targeted NGS for the identification of the disease-causing mutations in 16 Bulgarian patients with different IRDs. METHODS: We applied a customized NGS panel, including 125 genes associated with retinal and other eye diseases to the patients with hereditary retinopathies. RESULTS: Systematic filtering approach coupled with copy number variation analysis and segregation study lead to the identification of 16 pathogenic and likely pathogenic variants in 12/16 (75%) of IRD patients, 2 of which novel (12.5%): ABCA4-c.668delA (p.K223Rfs18) and RР1-c.2015dupA (p.K673Efs*25). Mutations in the ABCA4, PRPH2, USH2A, BEST1, RР1, CDHR1, and RHO genes were detected reaching a diagnostic yield between 42.9% for Retinitis pigmentosa cases and 100% for macular degeneration, Usher syndrome, and cone-rod dystrophy patients. CONCLUSION: Our results confirm the usefulness of targeted NGS approach based on frequently mutated genes as a comprehensive and successful genetic diagnostic tool for IRDs with significant impact on patients counseling.

A rare case of RGR/CDHR1 haplotype identified in Bulgarian patient with cone-rod dystrophy.

AIM: To present a rare clinical case of CDHR1-related retinopathy with cone and rod involvementconfirmed clinically, electrophysiologically and genetically as a cone-rod dystrophy. MATERIAL AND METHODS: A 26-year-old woman underwent detailed ophthalmic examinationincluding fundus photography, full-field and multifocal electroretinography, visual field testing, optical coherence tomography and fluorescein angiography, which established the clinical diagnosis. Next-generation sequencing of a custom panel including 140 of the most common genes for inherited retinal degenerations was used for mutation screening. RESULTS: The symptoms onset was two years ago included gradual loss of vision and photophobia. The clinical findings were reduced visual acuity, central and peripheral scotomas, sporadic pigmentary cells localized mainly in the peripheral retina, a thinner retina in the macula and peripherally, moderate retinal vessels attenuation and reduced cone and rod ERG responses. The genetic analysisfound that the patient was homozygous for two already reported mutations: RGR-c.196A>C (p.Ser66Arg) variant and a co-segregating frame-shift deletion in CDHR1-c.2522_2528delTCTCTGA (p.Ile841Serfs119*). Segregation analysis showed that the two mutations were transmitted by the asymptomatic heterozygous parents. CONCLUSION: The rare haplotype of RGR mutation co-segregating incis- with CDHR1 mutation in our patient has been previously described in Albanian patients with recessive retinal dystrophy. Our findings add further support to the hypothesis of a common ancestral haplotype spread in the Balkan population. The comprehensive clinical, electrophysiological and genetic testing of patients with rare hereditary retinal dystrophies is essential for the correct diagnosis and the choice of potential novel therapies.

Pattern electroretinography and retinal changes in patients with diabetes mellitus type 2.

OBJECTIVES: To objectively explore retinal neuronal function by pattern electroretinography (PERG) in patients with diabetes mellitus (DM) type 2 at different stages of diabetic retinopathy (DR). METHODS: A group of 84 patients with DM was studied, divided into three subgroups according to the degree of retinal changes. The first subgroup consisted of patients without DR (n=28), the second patients with initial DR (n=27) and the third patients with advanced DR (n=29). Controls were 47 healthy individuals. PERG was performed and latency and amplitude were analyzed. RESULTS: PERG results were affected in DM patients including the group without DR; abnormalities were more severe in patients with advanced DR. CONCLUSION: PERG could be used as an objective method providing evidence of early changes in retinal neuron function in DM patients, including at preclinical stages. It is useful for monitoring disease progression, as it is non-invasive, harmless, rapid, inexpensive and readily repeatable.

Reference values of pattern reversal visual evoked potentials in Bulgarian population.

AIMS: The aim of this study is to evaluate pattern visual evoked potentials as an objective electrophysiological method and to create reference values for Bulgarian population. METHODS AND MATERIALS: Standardized four-channel equipment 'Neuro-MEP 4' produced by 'Neurosoft' Company was used. A group of 47 healthy individuals (94 eyes) was studied. The stimulation was monocular, with a contrast-reversing pattern from black to white and vice versa. The investigation was performed with a three-channel recording with equipment adjustments according to the latest published ISCEV standard for pattern visual evoked potentials (2016). Based on a comprehensive overview of the available literature, a protocol of stimulating, amplifying and recording the obtained potentials has been created. The values of pattern visual evoked potential wave components, P50, N75, P100, N145 and P200, were measured. RESULTS: Based on a created protocol, latency and amplitudes of the individual wave components of pattern visual evoked potentials were obtained. The results were statistically processed to create reference values of all pattern visual evoked potentials components, which are used as reference of the laboratory for the Bulgarian population. CONCLUSION: Pattern visual evoked potentials are objective electrophysiological method which is used to diagnose and monitor numerous ophthalmological and neurological diseases as well as for objective study of visual acuity and visual field in children and aggravation. The creation of pattern visual evoked potentials reference values for the Bulgarian population and its implementation in clinical practice are of particular importance for studying the visual analyser function.