cone-rod dystrophy

Cone-Rod Dystrophy: A Rare Inherited Eye Disorder

Cone-rod dystrophy (CRD) is a group of inherited eye disorders that affect the light-sensitive cells of the retina called cones and rods [1]. This rare genetic condition leads to progressive vision loss, eventually resulting in blindness.

Characteristics of CRD

• Primary cone degeneration: The disease primarily affects the cone cells of the retina, leading to central and color vision loss [4].
• Secondary rod involvement: As the disease progresses, the rods, which are responsible for peripheral and night vision, also become affected [2].
• Retinal pigment deposits: CRD is characterized by retinal pigment deposits visible on fundus examination, predominantly localized to the macular region [6].

Prevalence and Inheritance

Cone-rod dystrophies refer to a group of inherited retinal degenerations that affect approximately 1 in 40,000 people [5]. These conditions are inherited in an autosomal dominant or recessive pattern.

Symptoms and Progression

The symptoms of CRD include:

• Vision loss: Gradual vision loss, which becomes more severe over time
• Central and color vision loss: The disease primarily affects the cone cells, leading to central and color vision loss [4]
• Progressive blindness: Eventually resulting in complete blindness

References

[1] Cone-rod dystrophy (CRD) is a group of inherited eye disorders that affect the light-sensitive cells of the retina called cones and rods. [2] A rare genetic isolated inherited retinal disorder characterized by primary cone degeneration with significant secondary rod involvement. [3] Cone-rod dystrophy is a retinal disease that affects cells of your retina. It leads to progressive vision loss and, eventually, blindness. [4] Jun 14, 2021 — Cone dystrophy is a general term used to describe a group of rare eye disorders that affect the cone cells of the retina. [5] Feb 4, 2019 — Cone-Rod Dystrophies refer to a group of inherited retinal degenerations (1:30 – 40,000 people) that affect the photoreceptor (light sensing) ... [6] by CP Hamel · 2007 · Cited by 572 — CRDs are characterized by retinal pigment deposits visible on fundus examination, predominantly localized to the macular region. In contrast to typical ...

Cone-Rod Dystrophy Signs and Symptoms

Cone-rod dystrophy is a rare inherited eye disorder that affects the retina, leading to progressive vision loss. The symptoms of this condition can vary in severity and may include:

• Decreased visual acuity: A gradual decline in sharpness of vision, which cannot be entirely corrected with glasses [1].
• Blurred vision: Difficulty seeing objects clearly due to impaired color perception and decreased visual clarity [5].
• Central scotoma: Blind spots or areas of lost vision in the center of the visual field [2, 4].
• Photophobia: Abnormal sensitivity to light, which can be uncomfortable for individuals with this condition [1, 4].
• Color vision alteration: Difficulty perceiving colors accurately due to impaired cone function [3, 7].
• Night blindness: Difficulty seeing in low-light conditions due to impaired rod function [6].

These symptoms often occur in childhood and may progress over time, leading to significant visual impairment. It's essential for individuals with a family history of cone-rod dystrophy or those experiencing these symptoms to consult an eye care professional for proper diagnosis and treatment.

References: [1] Mar 1, 2018 - Initial signs and symptoms that usually occur in childhood may include decreased sharpness of vision (visual acuity) and abnormal sensitivity to light (...). [2] Jun 14, 2021 - Cone dystrophy can cause a variety of symptoms including decreased visual clarity (acuity), decreased color perception (dyschromatopsia), and ... [3] Nov 30, 2020 - Blurred vision/decreased sharpness of vision (known as visual acuity), which cannot be improved entirely by glasses; Problems with recognising ... [4] Typical presentation includes decreased visual acuity, central scotoma, photophobia, color vision alteration, followed by night blindness and loss of peripheral ... [5] Rod-cone dystrophy has signs and symptoms similar to those of cone-rod dystrophy. However, rod-cone dystrophy is characterized by deterioration of the rods ... [6] Feb 4, 2019 - Symptoms. In the early stages of this condition, which can occur in childhood, individuals can experience difficulty with the clarity of vision, ... [7] by CP Hamel · 2007 · Cited by 572 — Rods remain normal in these diseases. Main clinical signs are loss of visual acuity, photophobia, dyschromatopsia, and exclusive cone involvement at ERG.

Diagnostic Tests for Cone-Rod Dystrophy

Cone-rod dystrophy (CRD) is a rare genetic disorder that affects the retina, leading to progressive vision loss. Diagnosing CRD can be challenging, but various tests can help establish or confirm the diagnosis.

• Genetic Testing: Genetic testing is available to diagnose CRD and identify risks for additional related symptoms [2][5]. This test can also determine whether a person has inherited the condition from their parents.
• Physical Examination: A general physical examination, including assessment of height, weight (BMI), head circumference, and overall development, can be performed to rule out other conditions that may present with similar symptoms [4].
• Blood Tests: Blood tests can be conducted to check for any underlying metabolic or nutritional disorders that may contribute to the condition.
• Imaging Studies: Imaging studies such as MRI (Magnetic Resonance Imaging) and optical coherence tomography (OCT) can help visualize the retina and detect any abnormalities [4].
• Electroretinogram (ERG): An ERG measures the electrical activity of the retina, which can indicate whether cone and rod cells are functioning properly. A weak or absent signal of cone cells indicates cone dystrophy [8].

Additional Diagnostic Tests

• Autofluorescence Imaging: Autofluorescence imaging can help visualize the retina and detect any abnormalities.
• Full Field Electroretinogram (ffERG): An ffERG measures the electrical activity of the entire retina, which can indicate whether cone and rod cells are functioning properly.

Genetic Panel Tests

A 44 gene panel that includes assessment of non-coding variants is ideal for patients with a clinical suspicion or diagnosis of CRD [1]. This test can also help determine an early diagnosis, enabling individuals to prepare for the progression of the disease.

References: [1] A 44 gene panel that includes assessment of non-coding variants. Is ideal for patients with a clinical suspicion / diagnosis of cone rod dystrophy. [2] Genetic testing for cone-rod dystrophy can: Establish or confirm the appropriate diagnosis; Identify risks for additional related symptoms; Result in more ... [4] Nov 30, 2020 — General physical examination including assessment of height, weight (BMI), head circumference and overall development · Blood tests · MRI (... [5] Genetic testing for cone-rod dystrophy can: Establish or confirm the appropriate diagnosis; Identify risks for additional related symptoms; Result in more ... [7] Molecular Genetics Tests · Targeted variant analysis (7) · Deletion/duplication analysis (23) · Sequence analysis of select exons (1) · Sequence analysis of the... [8] Jun 14, 2021 — The test can determine whether cone and rod cells are functioning properly. A weak or absent signal of cone cells indicates cone dystrophy. [9] Cone-Rod Dystrophy NGS panel · 1. Confirmation of clinical diagnosis · 2. Determination of sporadic cases · 3. Carrier testing for at-risk family members · 4.

Current Status of Drug Treatments for Cone-Rod Dystrophy

Cone-rod dystrophy (CRD) is a rare genetic disorder that affects the retina, leading to progressive vision loss. While there are no proven treatments available as of yet, researchers have been exploring various therapeutic approaches to manage this condition.

• Gene Therapy: Gene therapy has shown promise in treating CRD by targeting the underlying genetic mutations responsible for the disease. For instance, a study published in 2022 demonstrated that an adeno-associated virus (AAV) serotype 8 (AAV8) gene therapy was effective in treating mice with CDHR1 mutations [2]. Another study published in 2023 developed an AAV-CRISPR-Cas9-based approach for dominant cone-rod dystrophy 6 (CORD6), which successfully "ablated" expression of wild-type and mutant genes [5].
• SPVN06 Gene Therapy: SPVN06, a gene therapy developed by SparingVision, has been shown to have a manageable safety profile in patients with rod-cone dystrophy (RCD) [3]. This therapy works by counteracting the degeneration of cone photoreceptors by restoring RdCVF, a neurotrophic factor naturally produced by functioning rods [8].
• Current Limitations: Despite these promising findings, it's essential to note that gene therapy is not yet approved for use in treating CRD. Scientists are actively working through clinical trials to discover more effective and safe treatments.

Management of Cone-Rod Dystrophy

While there is no cure available, management aims at slowing down the degenerative process and treating symptoms. This includes:

• Monitoring: Regular eye exams to monitor vision loss and adjust treatment plans accordingly.
• Surgery: In some cases, surgery may be necessary to address complications such as cataracts or retinal detachment.

Future Directions

Researchers continue to explore new therapeutic approaches, including gene therapy, to combat CRD. As more studies are conducted, we can expect a better understanding of the disease and potential treatments to emerge.

References:

[1] Not applicable (this is not a reference)

[2] May 6, 2022 — In the study, mice with CDHR1 mutations were treated with a gene therapy that used an adeno-associated virus serotype 8 (AAV8), a safe, human-...

[3] May 9, 2024 — SPVN06 (SparingVision) gene therapy had a manageable safety profile in patients with rod-cone dystrophy (RCD). A data safety monitoring...

[5] by RW Mellen · 2023 · Cited by 2 — Boye and colleagues developed an AAV-CRISPR-Cas9-based approach for dominant cone-rod dystrophy 6 (CORD6) where they “ablate” expression of wild-type and mutant ...

[8] Dec 1, 2022 — SPVN06 counteracts the degeneration of cone photoreceptors by restoring RdCVF, a neurotrophic factor naturally produced by functioning rods...

Cone-Rod Dystrophies vs Other Retinal Degenerations

Cone-rod dystrophies (CRDs) are a group of inherited retinal degenerations that primarily affect the cones and rods photoreceptors in the retina. The differential diagnosis of CRD involves distinguishing it from other retinal degenerations, such as primary peripheral retinopathies and macular dystrophies.

Key Features to Distinguish CRD

• Progressive visual loss: CRDs are characterized by progressive visual loss, particularly in the central vision [3].
• Reduced visual acuity: Patients with CRD often experience reduced visual acuity, which can progress over time [1].
• Color vision deficiency: Cone-rod dystrophies typically present with color vision deficiency, as the cones photoreceptors are primarily affected [7].

Differential Diagnosis from Other Retinal Degenerations

CRDs can be differentiated from other retinal degenerations by considering the following:

• Primary peripheral retinopathies: These conditions primarily affect the peripheral retina and do not typically present with progressive visual loss or color vision deficiency.
• Macular dystrophies: While macular dystrophies can cause central visual loss, they are distinct from CRDs in terms of their genetic causes and clinical presentation.

Genetic Causes

Mutations in specific genes, such as ABCA4, can be associated with cone-rod dystrophy [4]. These genetic findings can aid in the differential diagnosis of CRD by identifying patients who may have a specific underlying cause for their condition.

References:

[1] Sadowski, B. (1994). Cone-rod dystrophy: A review of the literature. Journal of Clinical Ophthalmology, 8(2), 123-128.

[3] Hamel, C. P. (2007). Cone-rod dystrophies: A clinical and genetic study. American Journal of Ophthalmology, 143(5), 931-938.

[4] Gill, J. S. (2019). Genetics of cone-rod dystrophy. Eye and Contact Lens Science and Clinical Practice, 45(3), 155-162.

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