About 6 percent of patients with Leber Congenital Amaurosis (LCA), the leading cause of blindness among infants and toddlers, could belong to a genotype that deserves therapeutic attempts.

LCA is a genetic disorder that causes abnormalities in cells that receive light from the retina. The disorder causes the visual acuity to fall significantly from birth or early childhood and leads to blindness, and the prevalence is about three in 100,000 people worldwide. There is no known treatment except for gene therapy so far.

A Gangnam Severance Hospital research team led by Professor Han Jinu of the Department of Ophthalmology on Monday revealed the molecular genetic diagnosis of the next-generation sequencing analysis, genetic patterns, and phenotypes of 50 LCA patients.

The causative gene was found in 39 patients, accounting for 78 percent of the total. Causative genes found the most in the patients were Guanylate Cyclase 2D, Nicotinamide Nucleotide Adenylyltransferase 1, and Centrosomal protein 290 genes, which account for 20, 18, and 16 percent, respectively, of the total. Three patients, or 6 percent, had the copy number variation (CNV).

CNV is one of the factors that are not easily detected by the genetic test method, which makes the cause of the disease to be unknown. However, the research team said that the next-generation sequencing analysis could help identify the cause mutation more accurately by discovering the CNV. Only one patient with genotype, retinal pigment epithelium-specific 65, could receive gene therapy.

Besides, two patients suffered Senior Loken Syndrome, which has a high risk of kidney damage along with vision loss. Due to the risk, the research team said that medical professionals could try customized treatments, such as kidney transplants, if they found a causative gene at an early stage via gene analysis.

Professor Han said that 26 causative genes had been reported in the world, but gene analysis research is lacking in domestic patients.

“Through this study, we analyzed the genotype distribution of domestic patients and the relationship between each gene and the clinical pattern, and confirmed that the next-generation sequencing method could help patients with customized treatments with an accurate diagnosis,” Han said.

He added that reducing the cost of gene therapy, which is the only treatment and test, remains a challenge.

The study was a part of the academic service program of the Division of Rare Diseases at the Korea Centers for Disease Control and Prevention. The international journal, Molecular Vision, published the results on its latest issue.