[Molecular updates on Usher syndrome]

Extending the spectrum of CLRN1- and ABCA4-associated inherited retinal dystrophies caused by novel and recurrent variants using exome sequencing

Background

Inherited retinal dystrophies (IRDs) are characterized by extreme genetic and clinical heterogeneity. There are many genes that are known to cause IRD which makes the identification of the underlying genetic causes quite challenging. And in view of the emergence of therapeutic options, it is essential to combine molecular and clinical data to correctly diagnose IRD patients. In this study, we aimed to identify the disease‐causing variants (DCVs) in four consanguineous Jordanian families with IRDs and describe genotype–phenotype correlations.

Methods

Exome sequencing (ES) was employed on the proband patients of each family, followed by segregation analysis of candidate variants in affected and unaffected family members by Sanger sequencing. Simulation analysis was done on one novel CLRN1 variant to characterize its effect on mRNA processing. Clinical evaluation included history, slit‐lamp biomicroscopy, and indirect ophthalmoscopy.

Results

We identified two novel variants in CLRN1 [(c.433+1G>A) and (c.323T>C, p.Leu108Pro)], and two recurrent variants in ABCA4 [(c.1648G>A, p.Gly550Arg) and (c.5460+1G>A)]. Two families with the same DCV were found to have different phenotypes and another family was shown to have sector RP. Moreover, simulation analysis for the CLRN1 splice donor variant (c.433+1G>A) showed that the variant might affect mRNA processing resulting in the formation of an abnormal receptor. Also, a family that was previously diagnosed with nonsyndromic RP was found to have Usher syndrome based on their genetic assessment and audiometry.

Conclusion

Our findings extend the spectrum of CLRN1‐ and ABCA4‐associated IRDs and describe new phenotypes for these genes. We also highlighted the importance of combining molecular and clinical data to correctly diagnose IRDs and the utility of simulation analysis to predict the effect of splice donor variants on protein formation and function.

Psychological Stress in People with Dual Sensory Impairment through Usher Syndrome Type II

Introduction

Due to their dual, sensory impairment, people with Usher syndrome are assumed to have a high risk of stress. The purpose of this study was to assess stress in people with Usher syndrome type II (USH2) and the influence of personal variables such as age, gender, and employment on stress.

Methods

Two questionnaires were used: A self-developed questionnaire (SQ) to investigate the frequency and intensity of stress by external stressors within six life domains and the German standardized stress questionnaire Trierer Inventory of Chronic Stress (TICS) to compare frequency of stress between the USH2 sample group and a reference group ( n = 604). The questionnaires were filled in by an ad hoc sample of 262 persons with USH2 (response rate: 93%), mainly recruited from self-help groups (ages 17–79, mean age = 51; 53% female; 32% employed). Differences were determined by using methods of classical test theory.

Results

The evaluated SQ shows good indices in terms of item and factor analysis. The greatest stress was seen in the factor “Orientation and Mobility”; in TICS it was in the scale “Chronic Worry.” In TICS the USH2 sample showed significantly higher stress on scales that indicate a lack of social-emotional need fulfillment and less stress in those with high expectations ( p = .05). In both questionnaires, stress was dependent on personal variables.

Discussion

The results indicate the need for rehabilitation arrangements to reduce stress in people with USH2, especially in the areas of orientation and mobility, chronic worry, and social isolation. In intervention, particular attention should be paid to older, female, and unemployed people.

Implications for practitioners

Internal and external resources for people with dual sensory impairment need to be strengthened and systematic programs for learning how to cope with stress need to be established in order to provide clients with successful problem- and emotion-focused coping strategies.

Retinitis pigmentosa

Retinitis pigmentosa (RP) is an inherited retinal dystrophy caused by the loss of photoreceptors and characterized by retinal pigment deposits visible on fundus examination. Prevalence of non syndromic RP is approximately 1/4,000. The most common form of RP is a rod-cone dystrophy, in which the first symptom is night blindness, followed by the progressive loss in the peripheral visual field in daylight, and eventually leading to blindness after several decades. Some extreme cases may have a rapid evolution over two decades or a slow progression that never leads to blindness. In some cases, the clinical presentation is a cone-rod dystrophy, in which the decrease in visual acuity predominates over the visual field loss. RP is usually non syndromic but there are also many syndromic forms, the most frequent being Usher syndrome. To date, 45 causative genes/loci have been identified in non syndromic RP (for the autosomal dominant, autosomal recessive, X-linked, and digenic forms). Clinical diagnosis is based on the presence of night blindness and peripheral visual field defects, lesions in the fundus, hypovolted electroretinogram traces, and progressive worsening of these signs. Molecular diagnosis can be made for some genes, but is not usually performed due to the tremendous genetic heterogeneity of the disease. Genetic counseling is always advised. Currently, there is no therapy that stops the evolution of the disease or restores the vision, so the visual prognosis is poor. The therapeutic approach is restricted to slowing down the degenerative process by sunlight protection and vitaminotherapy, treating the complications (cataract and macular edema), and helping patients to cope with the social and psychological impact of blindness. However, new therapeutic strategies are emerging from intensive research (gene therapy, neuroprotection, retinal prosthesis).