Marinesco-Sjögren syndrome is a condition that has a variety of signs and symptoms affecting many tissues. People with Marinesco-Sjögren syndrome have clouding of the lens of the eyes (cataracts) that usually develops soon after birth or in early childhood. Affected individuals also have muscle weakness (myopathy) and difficulty coordinating movements (ataxia), which may impair their ability to walk. People with Marinesco-Sjögren syndrome may experience further decline in muscle function later in life.

Most people with Marinesco-Sjögren syndrome have mild to moderate intellectual disability. They also have skeletal abnormalities including short stature and a spine that curves to the side (scoliosis). Other features of Marinesco-Sjögren syndrome include eyes that do not look in the same direction (strabismus), involuntary eye movements (nystagmus), and impaired speech (dysarthria).

Affected individuals may have hypergonadotropic hypogonadism, which affects the production of hormones that direct sexual development. As a result, puberty is either delayed or absent.

Mutations in the SIL1 gene cause Marinesco-Sjögren syndrome. The SIL1 gene provides instructions for producing a protein located in a cell structure called the endoplasmic reticulum. Among its many functions, the endoplasmic reticulum folds and modifies newly formed proteins so they have the correct 3-dimensional shape. The SIL1 protein plays a role in the process of protein folding.

SIL1 gene mutations result in the production of a protein that has little or no activity. A lack of SIL1 protein is thought to impair protein folding, which could disrupt protein transport and cause proteins to accumulate in the endoplasmic reticulum. This accumulation likely damages and destroys cells in many different tissues, leading to ataxia, myopathy, and the other features of Marinesco-Sjögren syndrome.

Approximately one-third of people with Marinesco-Sjögren syndrome do not have identified mutations in the SIL1 gene. In these cases, the cause of the condition is unknown.

Normal Function

The SIL1 gene provides instructions for producing a protein located in a cell structure called the endoplasmic reticulum. Among its many functions, the endoplasmic reticulum folds and modifies newly formed proteins so they have the correct 3-dimensional shape. The SIL1 protein works with BiP, a protein that helps fold newly produced proteins into the proper shape and refold damaged proteins. To start this process, BiP attaches (binds) to a molecule called adenosine triphosphate (ATP). When BiP folds a protein, the ATP is converted to a similar molecule called adenosine diphosphate (ADP). Then the SIL1 protein releases ADP from BiP so that it can bind to another molecule of ATP and start the protein folding process again. Because of its role in helping BiP exchange ADP for ATP, the SIL1 protein is called a nucleotide exchange factor.

Health Conditions Related to Genetic Changes

Marinesco-Sjögren syndrome

More than a dozen mutations in the SIL1 gene have been found to cause Marinesco-Sjögren syndrome. Most of these mutations result in the production of a protein that has little or no activity. Defective SIL1 protein cannot remove ADP from BiP. BiP is then unable to bind to ATP and re-start the protein folding process. A disruption in protein folding impairs protein transport and causes proteins to accumulate in the endoplasmic reticulum. This accumulation likely damages and destroys cells in many different tissues, leading to poor coordination, muscle weakness, and the other features of Marinesco-Sjögren syndrome.

Other Names for This Gene

• BAP
• BiP-associated protein
• MSS
• SIL1 homolog, endoplasmic reticulum chaperone (S. cerevisiae)
• SIL1 protein
• SIL1_HUMAN
• ULG5

Genomic Location

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.

Marinesco-Sjögren syndrome appears to be a rare condition. More than 100 cases have been reported worldwide.