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Bietti crystalline dystrophy (BCD)

Bietti crystalline dystrophy (BCD)




Overview

      

Bietti crystalline dystrophy (BCD) is a rare, inherited eye condition characterized by tiny, glistening yellow-white lipid (fat) crystals in the retina and sometimes the cornea, leading to progressive vision loss.

Symptoms

• Night blindness (Nyctalopia): Trouble seeing clearly in dim light or at night.

• Side-vision loss (Peripheral visual field loss): Gradual loss of the outer or side fields of vision.

• Reduced sharpness (Decreased visual acuity): Blurry vision and difficulty with tasks like reading or recognizing faces.

• Impaired color vision: Difficulty telling certain colors apart.

• Asymmetrical progression: Vision changes and symptoms can happen at different rates or severity in each eye.

• Retinal crystals: Small, shiny, yellow-white sparkling deposits scattered across the retina.

• Corneal crystals: Tiny, fine glistening crystals located at the edge of the cornea (seen in about 25% to 33% of patients).

• Degeneration: Breakdown of the retinal pigment epithelium and thinning or hardening (sclerosis) of the underlying choroidal vessels.

Causes

• Gene Mutations: BCD is triggered by pathogenic variations or mutations in the CYP4V2 gene, which provides instructions for making an enzyme involved in lipid (fat) and steroid metabolism.

• Autosomal Recessive Inheritance: BCD is an autosomal recessive condition. A person must inherit two abnormal copies of the CYP4V2 gene—one from each parent—to develop the disease. Parents who each carry one copy are typically unaffected carriers with a 25% chance per pregnancy of having an affected child.

• Disrupted Lipid Metabolism: The mutated CYP4V2 enzyme fails to properly break down or process fatty acids. This metabolic failure leads to the abnormal buildup of complex lipid and fatty acid crystals inside the cells of the retina, cornea, and sometimes other systemic tissues like the liver.

Cellular Atrophy: The accumulation of these crystalline lipid deposits causes progressive damage, inflammation, and atrophy of the retinal pigment epithelium (RPE), photoreceptors, and choroidal vessels, leading to gradual vision loss.

Diagnosis

• Dilated Fundus Examination: An eye doctor looks for small, glistening yellow-white crystalline deposits across the retina, alongside atrophy of the retinal pigment epithelium (RPE), pigment clumping, and sclerosis (hardening/narrowing) of the choroidal vessels. About 25% to 50% of patients also have small crystals in the peripheral cornea.

• Optical Coherence Tomography (OCT): Spectral-domain OCT or ultra-widefield imaging identifies hyperreflective dot-like lesions and structural degeneration in the outer retina, photoreceptor layer, and RPE-Bruch's membrane complex.

• Electroretinography (ERG): Measures electrical responses of the retina to test for generalized rod and cone cell dysfunction.

• Humphrey Visual Field (HVF) Testing: Maps out peripheral and central visual field losses.

• Near-Infrared Reflectance (NIR): A noninvasive imaging method that tracks both early crystalline deposits and advanced choroidal vessel sclerosis.

• Molecular Genetic Testing: Definitive confirmation is achieved by identifying biallelic pathogenic variants (mutations) in the CYP4V2 gene via gene-targeted panels or genomic sequencing, especially when clinical features overlap with other conditions like retinitis pigmentosa.

Treatment

• Low-Vision Specialists: Referral to vision rehabilitation services, magnifying tools, and state resources for the blind helps patients adapt to progressive night blindness and visual field loss.

• Anti-VEGF Injections: Intravitreal anti-VEGF medication is used if patients develop active macular neovascularization (abnormal blood vessel growth in the macula).

• Genetic Counseling: Offered to patients and carriers to discuss inheritance patterns, risks to family members, and family planning.

• Regular Monitoring: Periodic evaluations by an ophthalmologist or retinal specialist to track progression.

• Gene Replacement/Augmentation Therapy: Investigational gene therapies (such as ZVS101e / rAAV2/8-hCYP4V2 and NGGT001) use a harmless viral vector to deliver a healthy copy of the CYP4V2 gene directly to retinal cells via subretinal injection.

• Clinical Trial Progress: Early-phase clinical trials (including Phase 1 and Phase 1/2 studies) have shown promising safety profiles and improvements in best-corrected visual acuity (BCVA) and retinal function. Researchers are actively working toward larger late-phase trials in the United States and globally.

Type of Doctor Department : An ophthalmologist

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