congenital stationary night blindness 1F

Congenital Stationary Night Blindness 1F (CSNB1F)

Congenital Stationary Night Blindness 1F, also known as complete congenital stationary night blindness type 1F, is a rare genetic disorder that affects the retina. It is characterized by an inability to see in low light or dark conditions.

Causes and Genetics

This condition is caused by compound heterozygous mutation in the LRIT3 gene on chromosome 4q25 [11]. This genetic mutation leads to abnormal signaling in the retina, resulting in visual deficits.

Symptoms and Characteristics

People with CSNB1F typically experience difficulty seeing and distinguishing objects in low light conditions. The symptoms are present from birth and tend to remain stable over time.

Classification and Types

Congenital stationary night blindness can be classified into two types based on electroretinographic findings: the Riggs type and the Schubert-Bornschein (S–B) type [12]. CSNB1F is not specifically mentioned as one of these types, but it is a subtype of congenital stationary night blindness.

References

• [11] A number sign (#) is used with this entry because of evidence that complete congenital stationary night blindness type 1F (CSNB1F) is caused by compound heterozygous mutation in the LRIT3 gene on chromosome 4q25.
• [12] Congenital stationary night blindness can be classified into 2 types based on electroretinographic findings 1: (i) the Riggs type, which is much less prevalent, where there are reduced a- and b-waves in response to a scotopic bright flash; and (ii) the Schubert–Bornschein (S–B) type with selective loss of the b-wave.

Common Signs and Symptoms of Congenital Stationary Night Blindness (CSNB)

People with CSNB may experience a range of symptoms, including:

• Night Blindness: The most common symptom is difficulty seeing in low light conditions. This can make it difficult to navigate through dark spaces or perform tasks that require good vision in dim light.
• Reduced Visual Acuity: Some individuals with CSNB may have reduced visual acuity, which can affect their ability to see objects clearly at a distance.
• Myopia (Nearsightedness): Many people with CSNB are nearsighted, meaning they can see close objects clearly but struggle to see distant ones.
• Nystagmus: Some individuals with CSNB may experience involuntary movements of the eyes, which can be noticeable when looking at a fixed point.
• Strabismus (Crossed Eyes): In some cases, people with CSNB may have crossed or misaligned eyes.

These symptoms are often subjective and may not be immediately apparent to those who live in well-lit environments

Diagnostic Tests for Congenital Stationary Night Blindness (CSNB) Type 1F

Congenital stationary night blindness type 1F is a rare genetic disorder that affects the retina, causing difficulty seeing and distinguishing objects in low light. Diagnosing CSNB type 1F typically involves a series of tests to confirm the condition and rule out other potential causes.

• Electroretinogram (ERG): This test measures the electrical responses of the retina to light stimuli. It is a crucial diagnostic tool for CSNB, as it can help identify the specific type of retinal dysfunction present in individuals with this condition [9].
• Genetic testing: Genetic testing can confirm the presence of mutations in the LRIT3 gene, which is associated with complete congenital stationary night blindness type 1F (CSNB1F) [11]. This test involves analyzing a DNA sample from an individual to identify any genetic abnormalities.
• Full-field electroretinograms (ERG): Full-field ERG measures the electrical responses of the retina to light stimuli, and is often used in conjunction with other diagnostic tests to confirm the diagnosis of CSNB [3].
• Visual acuity testing: Visual acuity testing can help assess an individual's ability to see objects clearly at different distances. In individuals with CSNB type 1F, visual acuity may be reduced, ranging from 20/30 to 20/200 [2].

It is essential to note that a comprehensive diagnostic evaluation should be performed by an experienced ophthalmologist or geneticist to confirm the diagnosis of CSNB type 1F and rule out other potential causes.

References: [2] - Congenital stationary night blindness (CSNB) is a non-progressive retinal disorder that is characterized by night or dim light vision disturbance or delayed dark adaptation, poor visual acuity (ranging from 20/30 to 20/200), myopia, nystagmus, strabismus, normal color vision and fundus abnormalities. [3] - Congenital stationary night blindness (CSNB) is a group of genetically determined, largely non-progressive retinal disorders that are characterized by reduced visual acuity, defective dark adaptation, refractive error, nystagmus, strabismus, and normal color vision. [9] - A number sign (#) is used with this entry because of evidence that complete congenital stationary night blindness type 1F (CSNB1F) is caused by compound heterozygous mutation in the LRIT3 gene. Diagnostic tests for CSNB include electroretinogram, full-field ERG, and genetic testing. [11] - In a 45-year-old woman with a diagnosis of complete CSNB who was negative for mutation in known CSNB genes, Zeitz et al. (2013) performed whole-exome sequencing to identify the LRIT3 gene mutations associated with this condition.

Current Drug Treatments for Congenital Stationary Night Blindness

While there is no known cure for congenital stationary night blindness (CSNB), researchers have been exploring various treatment options to alleviate symptoms. Here are some current drug treatments being investigated:

• Metoprolol, Bromocriptine, and Tamsulosin: A study published in 2019 found that pretreatment with a combination of these medications rescued the retina in all genetic backgrounds, starting at doses of 0.2 mg/kg metoprolol, 0.02 mg/kg bromocriptine, and 0.01 mg/kg tamsulosin [5].
• Gene Therapy: Gene therapy has shown promise in rapidly improving night vision in adults with congenital blindness, as reported by a Penn study in 2022 [3]. However, more research is needed to determine its effectiveness for CSNB.
• Vitamin A: Vitamin A can treat both genetic and acquired night blindness, according to a study published in 2023 [8].
• Beta Carotene: A clinical trial (NCT00569023) investigated the treatment of congenital stationary night blindness with an alga containing high doses of beta carotene [9].

Important Note

It's essential to consult with a medical professional for personalized advice on treating CSNB. These treatments may not be suitable or effective for everyone, and more research is needed to fully understand their potential benefits and risks.

References:

[3] Gene therapy rapidly improves night vision in adults with congenital blindness, Penn study finds (2022) [5] Pretreatment with metoprolol + bromocriptine + tamsulosin rescued the retina in all genetic backgrounds (2019) [8] Vitamin A can treat both genetic and acquired night blindness (2023) [9] Treatment of Congenital Stationary Night Blindness With an Alga Containing High Dose of Beta Carotene (NCT00569023)

The differential diagnosis for Congenital Stationary Night Blindness (CSNB) 1F involves ruling out other causes of visual disturbances and flecked retina.

• Other causes of flecked retina, as mentioned in Chapter 50, need to be considered.
• The large gene comprising 48 exons that encodes a voltage-dependent L-type calcium channel subunit alpha-1F is expressed within the rod and cone active zones in the outer plexiform layer. This information suggests that CSNB 1F is associated with defective visual signal transduction or transmission in the rod photoreceptors, the rod ON bipolar cell synapses, or defective retinoid recycling in the retinal pigment epithelium (RPE) [13].

To make a differential diagnosis for CSNB 1F, it's essential to consider the following factors:

• Clinical presentation: The symptoms and signs of CSNB 1F, such as night blindness, poor visual acuity, myopia, and thinning of the inner nuclear layer.
• Genetic testing: To confirm the presence of mutations in the gene encoding the voltage-dependent L-type calcium channel subunit alpha-1F.
• Full-field electroretinograms (ERG): To assess the function of the rod photoreceptors and the retinal pigment epithelium.

By considering these factors, healthcare professionals can make an accurate differential diagnosis for CSNB 1F and rule out other potential causes of visual disturbances.