Senior Loken Syndrome

Other Names: Senior-Loken Syndrome; Renal dysplasia retinal aplasia; Renal-retinal syndrome; Juvenile nephronophthisis with Leber amaurosis; Loken-Senior syndrome

Senior-Løken syndrome is a rare disorder characterized by the combination of two specific features: a kidney condition called nephronophthisis and an eye condition known as Leber congenital amaurosis.

Epidemiology

Senior-Løken syndrome is a rare disorder, with an estimated prevalence of about 1 in 1 million people worldwide. Only a few families with the condition have been described in the medical literature.

Cause

Senior-Løken syndrome can be caused by mutations in one of at least five genes. The proteins produced from these genes are known or suspected to play roles in cell structures called cilia. Cilia are microscopic, finger-like projections that stick out from the surface of cells; they are involved in signaling pathways that transmit information between cells. Cilia are important for the structure and function of many types of cells, including certain cells in the kidneys. They are also necessary for the perception of sensory input (such as vision, hearing, and smell). Mutations in the genes associated with Senior-Løken syndrome likely lead to problems with the structure and function of cilia. Defects in these cell structures probably disrupt important chemical signaling pathways within cells. Although researchers believe that defective cilia are responsible for the features of this disorder, it remains unclear how they lead specifically to nephronophthisis and Leber congenital amaurosis. Some people with Senior-Løken syndrome do not have identified mutations in one of the five genes known to be associated with the condition. In these cases, the genetic cause of the disorder is unknown.

Inheritance

Autosomal recessive inheritance, a 25% chance

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Signs and symptoms

Nephronophthisis causes fluid-filled cysts to develop in the kidneys beginning in childhood. These cysts impair kidney function, initially causing increased urine production (polyuria), excessive thirst (polydipsia), general weakness, and extreme tiredness (fatigue). Nephronophthisis leads to end-stage renal disease (ESRD) later in childhood or in adolescence. ESRD is a life-threatening failure of kidney function that occurs when the kidneys are no longer able to filter fluids and waste products from the body effectively. Leber congenital amaurosis primarily affects the retina, which is the specialized tissue at the back of the eye that detects light and color. This condition causes vision problems, including an increased sensitivity to light (photophobia), involuntary movements of the eyes (nystagmus), and extreme farsightedness (hyperopia). Some people with Senior-Løken syndrome develop the signs of Leber congenital amaurosis within the first few years of life, while others do not develop vision problems until later in childhood.

For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. 80%-99% of people have these symptoms

• Abnormality of retinal pigmentation
• Global developmental delay
• Hypertension
• Retinal dystrophy(Breakdown of light-sensitive cells in back of eye)
• Short stature(Decreased body height)
• Stage 5 chronic kidney disease

30%-79% of people have these symptoms

• Nephronophthisis
• Premature ovarian insufficiency(Early menopause)
• Progressive visual loss(Progressive loss of vision)

5%-29% of people have these symptoms

• Abnormality of bone mineral density
• Ataxia
• Cataract(Clouding of the lens of the eye)
• Cone-shaped epiphysis(Cone-shaped end part of bone)
• Congenital hepatic fibrosis(Excessive buildup of connective tissue and scarring of liver at birth)

Diagnosis

Molecular Genetics Tests include: Deletion/duplication analysis Sequence analysis of select exons Sequence analysis of the entire coding region Targeted variant analysis

Treatment

Treatment during earlier stages of kidney disease in children includes maintaining a healthy balance of fluid and electrolytes. End-stage kidney disease requires dialysis, or kidney transplantation. After transplantation, kidney damage does not occur again. End-stage kidney disease can be life-threatening if not treated. There is currently no treatment to prevent or stop the progression of vision loss due to retinal dystrophy, but various low-vision aids may be helpful for those who have remaining vision.

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NIH genetic and rare disease info

• NIH info on Senior Loken Syndrome

Senior Loken Syndrome is a rare disease.

Senior Loken Syndrome Resources
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