Senior-Loken Syndrome (SLS) is a genetic disorder, meaning it is caused by changes, or mutations, in a person's DNA. Understanding the genetic basis of SLS is crucial for accurate diagnosis, predicting disease progression, and making informed decisions about family planning.
SLS is inherited in an autosomal recessive pattern. "Autosomal" means the mutated gene is located on one of the non-sex chromosomes, meaning it affects males and females equally. "Recessive" means that for a child to develop the syndrome, they must inherit two copies of the mutated gene—one from each parent. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene but typically do not show any signs or symptoms of the condition themselves. They are known as "carriers."
When two carriers have a child, there is a 25% chance with each pregnancy that the child will inherit both mutated genes and develop SLS. There is a 50% chance the child will inherit one mutated gene and be a carrier like the parents, and a 25% chance the child will inherit two normal genes and be neither affected nor a carrier.
Scientists have identified mutations in several different genes that can cause SLS. The most common genes involved belong to the NPHP (nephronophthisis) family, including NPHP1, NPHP3, NPHP4, IQCB1 (also known as NPHP5), and CEP290 (also known as NPHP6). These genes provide instructions for making proteins that are essential for the normal function of cilia—microscopic structures that act like antennas on the surface of cells. In the retina, cilia are crucial for the function of photoreceptor cells, and in the kidneys, they are vital for the cells lining the kidney tubules. Mutations in these genes disrupt the cilia, leading to the dual symptoms of SLS.
Genetic testing is highly recommended for individuals suspected of having SLS. A confirmed genetic diagnosis can help clarify the specific subtype of the disease, guide medical management, and determine eligibility for future clinical trials. Furthermore, genetic counseling is an invaluable resource for families. A genetic counselor can explain the inheritance pattern in detail, discuss the risks to other family members, and outline options for family planning, such as carrier testing for relatives or preimplantation genetic testing (PGT) for future pregnancies.
Please note that this article is for informational purposes only. Patients and families should always consult their healthcare provider or a specialist for personalized medical advice and treatment plans.