Sotos syndrome is a rare genetic disorder characterized by excessive physical growth during the first years of life. Excessive growth often starts in infancy and continues into the early teen years. The disorder may be accompanied by autism,mild intellectual disability, delayed motor, cognitive, and social development, hypotonia (low muscle tone), and speech impairments. Children with Sotos syndrome tend to be large at birth and are often taller, heavier, and have relatively large skulls (macrocephaly) than is normal for their age.

SYMPTOMS

This syndrome is characterized by overgrowth and advanced bone age. Affected individuals are dysmorphic, with macrodolichocephaly, downslanting palpebral fissures and a pointed chin. The facial appearance is most notable in early childhood. Affected infants and children tend to grow quickly; they are significantly taller than their siblings and peers, and have an unusually large skull and large head. Adult height is usually in the normal range, although Broc Brown has the condition and was named the world's tallest teenager.Individuals with Sotos syndrome often have intellectual impairment and most also display autistic traits. Frequent behavioral impairments include attention deficit hyperactivity disorder (ADHD), phobias, obsessive compulsive disorder, tantrums, and impulsive behaviors (impulse control disorder).

CAUSES

Mutations in the NSD1 gene cause Sotos syndrome. The NSD1 gene provides instructions for making a protein (histone methyltransferase) that is involved in normal growth and development. The function of this protein is unknown, however. In the Japanese population, the most common genetic change leading to Sotos syndrome deletes genetic material from the region of chromosome 5 containing the NSD1 gene. In other populations, small mutations within the NSD1 gene occur more frequently. Genetic changes involving the NSD1 gene prevent one copy of the gene from producing any functional protein. It is unclear how a reduced amount of this protein during development leads to learning disabilities, overgrowth, and the other features of Sotos syndrome.

DIAGNOSIS

Diagnosis is based on physical examination, looking for excessive growth among other symptoms. There are no biochemical markers for the disease.