Congenital stationary night blindness 1C (CSNB1C) is a rare genetic disorder that affects vision, particularly in low-light conditions. It is a subtype of congenital stationary night blindness, a group of inherited retinal disorders characterized by impaired night vision. Congenital stationary night blindness (CSNB) is a group of rare, clinically heterogeneous, nonprogressive retinal disorders that appear during childhood. The genes involved in the different forms of CSNB encode proteins involved in the phototransduction cascade that are important in retinal signaling from photoreceptors (cones and rods) to adjacent nerve cells.
Congenital stationary night blindness 1C genetic testing is included in Diagnostiki Athinon Monogenic Diseases Genetic Testing along with approximetaly 100 other inherited diseases, including cystic fibrosis (71 mutations) and hereditary breast cancer (genes BRCA1 415 mutations & BRCA2 419 mutations).
Critical features of CSNB1C include:
- Genetic Basis: CSNB1C is caused by mutations in the CACNA1F gene. This gene provides instructions for making a protein that plays a crucial role in the function of photoreceptor cells in the retina.
- Inheritance: CSNB1C is typically inherited in an X-linked recessive manner, meaning the defective gene is on the X chromosome. As a result, the condition is more commonly observed in males. Females who carry one mutated gene may be unaffected carriers.
- Vision Impairment: Individuals with CSNB1C experience difficulty seeing in low-light conditions, such as at night or in dimly lit environments. Daytime vision is generally normal.
- Nystagmus: Many individuals with CSNB1C may exhibit involuntary eye movements, known as nystagmus, which can contribute to visual impairment.
- Electroretinography (ERG): Diagnostic tests, such as electroretinography, can help confirm the presence of CSNB1C. ERG measures the electrical responses of the retina to light stimulation, and in individuals with CSNB1C, the response is abnormal.
- Treatment and Management: Currently, there is no cure for CSNB1C, and treatment focuses on managing symptoms. Visual aids and devices designed to assist with low-light vision may be helpful.
- Prognosis: The prognosis for individuals with CSNB1C varies. While the condition does not worsen over time, managing day-to-day activities and adapting to low-light environments may pose challenges.
Genetic counseling is essential for families affected by CSNB1C to understand the inheritance pattern and potential risks.
Congenital stationary night blindness may be caused by defects in up to 17 genes, including TRPM1, which is affected in CSNB type 1C.
Congenital stationary night blindness can have an X-linked or autosomal recessive inheritance pattern. Forty percent of cases of complete-type CBNS are represented by mutations in the NYX and GRM6 genes, which are genes involved in the phototransduction cascade from retinal rods to bipolar neurons. However, to date, 60% of cases of congenital stationary night blindness remain unassociated with mutations in a specific gene. It is currently thought that this 60% is due to mutations in the TRPM1 gene and that these cases follow an autosomal recessive inheritance pattern.
The TRPM1 gene codes for a cation channel in the membrane of the dendritic tips of ON-bipolar cells. These cells are neurons that connect the photoreceptors (cones and rods) with the ganglion cells located in the outermost part of the retina and from which the optic nerve originates. Mutations in this gene can cause a deficiency in signaling and, therefore, in the activation of bipolar neurons, leading to the development of congenital stationary night blindness 1C.
This test analyzes the seven most frequent pathogenic mutations of the TRPM1 gene.
With the technique used for genetic testing, only the gene's specific mutations, which are the most important and frequent in the literature, are analyzed. However, it should be noted that there are likely other gene or chromosomal mutations in the gene to be tested, which cannot be identified with this method. Different analysis techniques can be used for these cases, such as, e.g., next-generation sequencing (NGS).
