Leber congenital amaurosis (LCA) is a group of inherited retinal disorders causing early-onset severe visual impairment or blindness from birth. It is the most common genetic cause of blindness in children. LCA arises from mutations in any one of at least 18 genes that are important for the normal function and development of the light-sensing photoreceptor cells in the retina.
Signs and Symptoms of Leber Congenital Amaurosis
The signs and symptoms of LCA typically appear within the first year of life. Babies with LCA often have nystagmus (involuntary eye movements), poor contact lens correction, and sluggish or abnormal pupils. Most individuals with LCA have severely reduced vision or no vision by adulthood. Some symptoms may include:
- Poor vision from birth or infancy, with little to no usable sight
- Sensitivity to bright light (photophobia)
- Rapid jerky eye movements (nystagmus)
- Reduced or no response of pupils to light (sluggish pupils)
- Rapid visual decline in early childhood
- Difficulties with night vision and side (peripheral) vision
Causes of Leber Congenital Amaurosis
Leber Congenital Amaurosis is inherited in an autosomal recessive manner, meaning two copies of a mutated gene - one from each parent - are required to cause the disorder. To date, mutations in at least 18 genes have been identified as causing LCA. Some of the genes and their functions include:
- CEP290: Important for light sensing pathways in photoreceptor cells
- GUCY2D: Encodes an enzyme crucial for phototransduction
- CRB1: Involved in photoreceptor cell development and function
- AIPL1: Plays a role in photoreceptor maintenance
- RPE65: Required for production of chemicals needed for vision
- LCA5/RPGRIP1: Important for cell division and growth of photoreceptors
- LRAT: Catalyzes a step in the visual cycle of the retina
Diagnosis of LCA
There is no single test to diagnose LCA, and diagnosis involves a full eye exam by an ophthalmologist along with genetic testing. Diagnostic tests may include:
- Complete eye exam including visual acuity tests and funduscopic exam
- Electroretinography (ERG): Measures electrical activity in the retina in response to light
- Optical coherence tomography (OCT): Provides cross-sectional images of the retina
- Genetic testing of known LCA genes through DNA testing of blood sample
Treatment and Management of LCA
Currently there is no cure for LCA, so treatment aims to maximize remaining vision and manage symptoms. Specific treatment approaches may include:
- Corrective lenses like telescopes, high-powered glasses, or contact lenses
- Low vision aids and adaptive equipment for daily living
- Mobility and orientation training
- Genetic counseling for families regarding risk of future children
- Experimental gene therapy clinical trials for specific LCA genetic subtypes
Gene Therapy Clinical Trials
Promising advances are being made through experimental gene therapy clinical trials which aim to deliver functional copies of missing or mutated LCA genes directly into the retina. Trials are still in progress, but initial results have been highly encouraging for certain genetic subtypes. Some key gene therapy trials include:
- RPE65-deficiency: Multicenter trials using AAV vector have shown lasting vision improvements.
- CEP290-deficiency: Ongoing trials using AAV vector show safety and signs of vision improvement.
- GUCY2D-deficiency: Early stage trials exploring CRISPR/Cas9 gene editing approach ongoing.
- Other LCA genes: Preclinical research underway to develop therapies targeting additional genes.
Prognosis and Outlook
The long-term prognosis for individuals with LCA depends on the genetic cause. Vision generally continues to decline slowly over time. However, with low vision aids and rehabilitation, quality of life can be good. Gene therapy trials are extremely promising and may eventually provide functional restoration of vision for many patients. Continued research aims to develop therapies for an increasing number of LCA subtypes.
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