CDHR1-Related Retinal Degeneration: A Review of the Preclinical Potential of Gene Augmentation Therapy
Background
A review of the clinical features and treatment approaches for CDHR1-related retinal degeneration discusses the potential of gene augmentation therapy observed in mouse models and the need for accurate diagnosis. Variants in CDHR1 cause autosomal recessive retinal degeneration, which presents in three forms: macular dystrophy, cone-rod dystrophy, and retinitis pigmentosa. The review explains that CDHR1-related macular dystrophy is often misdiagnosed because its clinical features resemble those of advanced dry age-related macular degeneration (AMD). It also links possible underdiagnosis to the fact that “silent” nucleotide substitutions, previously overlooked in genetic testing, are often responsible for CDHR1-related macular dystrophy.
Key findings
CDHR1 is an atypical cadherin protein highly expressed in photoreceptors, including cones and rods, which receive visual information. It is essential for maintaining the higher-order structure of the outer segment, a key light-sensing structure. In the preclinical data described in the review, subretinal injection of adeno-associated virus (AAV) gene augmentation therapy into a CDHR1-deficient mouse model was associated with long-term improvements in retinal morphology, structure, function, and behavioral measures. Photoreceptor outer segments, which had been shortened and disorganized in the disease model, recovered to their full length, and photoreceptor survival was prolonged. The authors present this restoration and prolonged survival as the key mechanism explaining the recovery in functional and behavioral measures.
These findings, however, are preclinical evidence from mice. The review suggests that AAV gene therapy might also help in macular dystrophy or retinitis pigmentosa associated with hypomorphic variants, in which some gene function remains, but it does not establish treatment efficacy in patients. The provided abstract does not report the number of animals, effect sizes, or specific follow-up duration.
The review also presents a flowchart to support clinical differential diagnosis. Because CDHR1-related macular dystrophy shares clinical features with macular dystrophies associated with ABCA4, PRPH2, and GUCY2D, the flowchart is intended to guide differentiation among these conditions. The provided abstract does not report results validating the flowchart’s diagnostic accuracy.
Implications and outlook
The coding sequence of CDHR1 can be packaged in AAV, a feature that supports the development of gene augmentation therapy. The authors describe a potentially long window for intervention in macular dystrophy and a sizable patient population that could be eligible for treatment, and they discuss the prospect of clinical trials. The abstract does not specify the intervention window or patient numbers, nor does it confirm a timeline for clinical trial initiation or approval.
The clinical resemblance to dry AMD underscores why accurate assessment of the clinical presentation and genetic confirmation matter in CDHR1-related disease. However, it is too early to conclude that confirmation alone determines treatment eligibility or can prevent vision loss in patients. Whether the results seen in animal models can be reproduced in people, and how long safety and efficacy are maintained, remain questions to resolve before clinical application.
Source: Progress in Retinal and Eye Research review abstract.
CDHR1 is a recently identified cause of autosomal recessive retinal degeneration manifesting as three distinct clinical phenotypes: macular dystrophy, cone-rod dystrophy or retinitis pigmentosa. In this review, we summarise the discovery and characterisation of CDHR1, clinical phenotypes, natural history and therapeutic approaches including gene supplementation and CRISPR gene editing. CDHR1 is a non-classical cadherin that is highly expressed in cone and rod photoreceptors and is essential for the higher-order organisation of the functionally critical outer segments. Promising pre-clinical data show that AAV gene supplementation therapy delivered by subretinal injection can lead to long-term morphological, structural, functional and behavioural improvements in the Cdhr1 knockout mouse model. Notably, CDHR1 supplementation restored full-length photoreceptor outer segments that are usually shortened and disorganised in disease models and prolonged photoreceptor survival - key mechanisms for the functional and behavioural rescue effects that were observed. The disease is likely to be underdiagnosed because CDHR1-associated macular dystrophy - likely to be the most common disease phenotype - is most often caused by a 'silent' nucleotide substitution that has previously been overlooked by genetic testing. Since the macular dystrophy phenotype has phenotypic similarities to advanced dry age-related macular degeneration (AMD), misdiagnoses are common. CDHR1-associated macular dystrophy also shares phenotypic features with a variety of monogenic masquerades such as ABCA4, PRPH2 and GUCY2D-associated macular dystrophies; we present a flowchart to guide the clinical distinction of these disorders which is now critical for patients as their treatments diverge. AAV gene therapy may be beneficial across the CDHR1 disease spectrum - including those with hypomorphic variants associated with macular dystrophy or retinitis pigmentosa. The coding sequence fits into AAV and with the
In clinical practice, this review provides context for distinguishing CDHR1-related disease from dry AMD and other inherited macular dystrophies with similar features. For example, when assessing a patient with similar macular lesions, clinicians might consider the clinical presentation alongside genetic test results and review silent substitutions that may have been overlooked in earlier testing. Accurate phenotypic assessment and genetic confirmation provide a basis for considering potential participants in future CDHR1-targeted therapy research. For development, the ability to package the coding sequence in AAV and the findings of outer-segment recovery and prolonged photoreceptor survival in mice support further research. However, the performance of the diagnostic flowchart, patient recruitment efficiency, preservation of vision in people, and shortened development timelines have not been demonstrated.