Smith-Kingsmore Syndrome

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Smith-Kingsmore syndrome is a neurological disorder characterized by a head that is larger than normal (macrocephaly), intellectual disability, and seizures. In some people with this condition, the ability to speak is delayed or never develops. Some children with Smith-Kingsmore syndrome have neurodevelopmental conditions known as attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorder, which is characterized by impaired communication and social interaction. Structural brain abnormalities may also be present in affected individuals. For example, one or both sides of the brain may be enlarged (hemimegalencephaly or megalencephaly) or have too many ridges on the surface (polymicrogyria), or the fluid-filled spaces near the center of the brain (ventricles) may be bigger than normal (ventriculomegaly).

Mutations in a gene called MTOR cause Smith-Kingsmore syndrome. The protein produced from this gene, called mTOR, is a key piece of two groups of proteins, known as mTOR complex 1 (mTORC1) and mTOR complex2 (mTORC2). These two complexes relay signals inside cells that regulate protein production and control several cellular processes, including growth, division, and survival. This mTOR signaling is especially important for growth and development of the brain, and it plays a role in a process called synaptic plasticity, which is the ability of the connections between nerve cells (synapses) to change and adapt over time in response to experience. Synaptic plasticity is critical for learning and memory.

Smith-Kingsmore syndrome is a rare condition with an unknown prevalence.

Smith-Kingsmore syndrome follows an autosomal dominant inheritance pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. Most cases result from new (de novo) mutations in the gene that occur during the formation of reproductive cells (eggs or sperm) in an affected individual’s parent or in early embryonic development. Rarely, people with Smith-Kingsmore syndrome inherit the altered gene from an unaffected parent who has an MTOR gene mutation only in their sperm or egg cells. This phenomenon is called germline mosaicism.

Published Date: January 01, 2019
Published By: National Institutes of Health