Is tuberous sclerosis (TSC) inherited?

Dr. Aria Fallah, MD

Tuberous sclerosis (TSC) can be inherited. There are two major genes that can lead to a diagnosis of tuberous sclerosis complex. Either a mutation in the TSC1 gene or a mutation in the TSC2 gene. TSC1 tends to be more the inherited form of the disease. TSC1 is thought of as the familial type as opposed to the TSC2 type, which is commonly associated with more spontaneous mutations. So, these are children with tuberous sclerosis complex that don't have any of their parents affected with tuberous sclerosis complex.

There's a certain inheritance pattern of this gene and it's an autosomal dominant pattern. That means that children have about a 50 percent chance of inheritance from either parent that may be affected with this disorder. It's much more common to have the spontaneous form of the disorder, which is usually associated with a mutation in the TSC2 gene, as opposed to TSC1 gene.

Two-thirds of the time, TSC is caused by a spontaneous mutation. This is a child that has developed TSC from a mutation in the DNA, but that mutation is not found in the parents. Less than half of the children affected by TSC have the familial or the inherited subtype of TSC.

Although some individuals inherit the disorder from a parent with tuberous sclerosis complex (TSC), most cases occur sporadically due to new, spontaneous mutations in TSC1 or TSC2. In this situation, neither parent has the disorder or the faulty gene(s). Instead, a faulty gene first occurs in the affected individual.

In familial cases, TSC is an autosomal dominant disorder, which means that the disorder can be transmitted directly from parent to child. In such cases, only one parent needs to have the faulty gene in order to pass it on to a child. If a parent has TSC, each offspring has a 50 percent chance of developing the disorder. Children who inherit TSC may not have the same symptoms as their parent, and may have either a milder or a more severe form of the disorder.

Rarely, individuals acquire TSC through a process called gonadal mosaicism. These patients have parents with no apparent defects in the two genes that cause the disorder. Yet, these parents can have a child with TSC because a portion of one of the parent's reproductive cells (sperm or eggs) can contain the genetic mutation without the other cells of the body being involved. In cases of gonadal mosaicism, genetic testing of a blood sample might not reveal the potential for passing the disease to offspring.

This answer is based on source information from the National Institute of Neurological Disorders and Stroke.

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