Sotos syndrome (also known as cerebral gigantism) is a rare genetic disorder caused by mutation in the NSD1 gene on chromosome 5. It is characterized by excessive physical growth during the first few years of life. Children with Sotos syndrome tend to be large at birth and are often taller, heavier, and have larger heads (macrocrania) than is normal for their age.

Symptoms of the disorder, which vary among individuals, include:

• A disproportionately large and long head with a slightly protrusive forehead and pointed chin
• Large hands and feet
• Hypertelorism (an abnormally increased distance between the eyes)
• Down-slanting eyes

The disorder is often accompanied by:

• Mild cognitive impairment
• Delayed motor, cognitive, and social development
• Hypotonia (low muscle tone)
• Speech impairments

Clumsiness, an awkward gait, and unusual aggressiveness or irritability may also occur. Although most cases of Sotos syndrome occur sporadically (meaning they are not known to be inherited), familial cases also have been reported.

There is no standard course of treatment for Sotos syndrome. Treatment is symptomatic.

Sotos syndrome is not a life-threatening disorder and individuals with the disorder may have a normal life expectancy. The initial abnormalities of Sotos syndrome usually resolve as the growth rate becomes normal after the first few years of life. Developmental delays may improve in the school-age years, and adults with Sotos syndrome are likely to be within the normal range for intellect and height. However, coordination problems may persist into adulthood.

Sotos syndrome is a disorder characterized by a distinctive facial appearance, overgrowth in childhood, and learning disabilities or delayed development of mental and movement abilities. Characteristic facial features include a long, narrow face; a high forehead; flushed (reddened) cheeks; and a small, pointed chin. In addition, the outside corners of the eyes may point downward (down-slanting palpebral fissures). This 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 head. However, adult height is usually in the normal range.

People with Sotos syndrome often have intellectual disability, and most also have neurodevelopmental disorders. Conditions that commonly occur in people with Sotos syndrome include autism spectrum disorder, attention-deficit/hyperactivity disorder (ADHD), phobias, obsessions and compulsions, tantrums, and impulsive behaviors. Problems with speech and language are also common. Affected individuals often have a stutter, a monotone voice, and problems with sound production. Additionally, weak muscle tone (hypotonia) may delay other aspects of early development, particularly motor skills such as sitting and crawling.

Other signs and symptoms of Sotos syndrome can include an abnormal side-to-side curvature of the spine (scoliosis), seizures, heart or kidney defects, hearing loss, and problems with vision. Some infants with this disorder experience yellowing of the skin and whites of the eyes (jaundice) and poor feeding.

A small percentage of people with Sotos syndrome have developed cancer, most often in childhood, but no single form of cancer occurs most frequently with this condition. It remains uncertain whether Sotos syndrome increases the risk of specific types of cancer. If people with this disorder have an increased cancer risk, it is only slightly greater than that of the general population.

Mutations in the NSD1 gene are the primary cause of Sotos syndrome, accounting for up to 90 percent of cases. Other genetic causes of this condition have not been identified.

The NSD1 gene provides instructions for making a protein that functions as a histone methyltransferase. Histone methyltransferases are enzymes that modify structural proteins called histones, which attach (bind) to DNA and give chromosomes their shape. By adding a molecule called a methyl group to histones (a process called methylation), histone methyltransferases regulate the activity of certain genes and can turn them on and off as needed. The NSD1 protein controls the activity of genes involved in normal growth and development, although most of these genes have not been identified.

Genetic changes involving the NSD1 gene prevent one copy of the gene from producing any functional protein. Research suggests that a reduced amount of NSD1 protein disrupts the normal activity of genes involved in growth and development. However, it remains unclear exactly how a shortage of this protein during development leads to overgrowth, learning disabilities, and the other features of Sotos syndrome.

Normal Function

The NSD1 gene provides instructions for making a protein that functions as a histone methyltransferase. Histone methyltransferases are enzymes that modify structural proteins called histones, which attach (bind) to DNA and give chromosomes their shape. By adding a molecule called a methyl group to histones (a process called methylation), histone methyltransferases control (regulate) the activity of certain genes and can turn them on and off as needed. The NSD1 enzyme controls the activity of genes involved in normal growth and development, although most of these genes have not been identified.

Health Conditions Related to Genetic Changes

Sotos syndrome

More than 380 mutations in the NSD1 gene have been identified in people with Sotos syndrome. The most common mutation in the Japanese population deletes genetic material from the region of chromosome 5 that contains the NSD1 gene. In most other populations, mutations within the gene itself are more frequent. These mutations include insertions or deletions of a small amount of DNA and changes in single DNA building blocks (base pairs) that make up the gene. Most mutations prevent one copy of the NSD1 gene from making any enzyme or lead to the production of an abnormally small, nonfunctional version of the enzyme. Research suggests that a reduced amount of the NSD1 enzyme disrupts the normal activity of genes involved in growth and development. However, it remains unclear exactly how a shortage of this enzyme during development leads to overgrowth, learning disabilities, and the other signs and symptoms of Sotos syndrome.

Cancers

A change involving the NSD1 gene is associated with a blood cancer called childhood acute myeloid leukemia. This change occurs when part of chromosome 5 breaks off and reattaches to part of chromosome 11. This change is acquired during a person's lifetime and is present only in cancer cells. This type of genetic change, called a somatic mutation, is not inherited. The rearrangement of genetic material involved in childhood acute myeloid leukemia, known as a translocation, abnormally fuses the NSD1 gene on chromosome 5 with the NUP98 gene on chromosome 11. Research shows that the fused NUP98-NSD1 gene turns on genes that promote the growth of immature blood cells and blocks processes that would turn the genes off. The resulting overgrowth of these immature cells leads to development of acute myeloid leukemia.

A different type of alteration involving the NSD1 gene is associated with a cancer of nerve tissue called neuroblastoma and a type of brain cancer called glioma. This alteration, known as promoter hypermethylation, turns off the production of the NSD1 enzyme. Researchers speculate that without NSD1, the activity of one or more genes involved in cell growth and division is uncontrolled. As a result, the cells can grow and divide unchecked, leading to the development of cancer.

Other Names for This Gene

• androgen receptor-associated coregulator 267
• ARA267
• histone-lysine N-methyltransferase, H3 lysine-36 and H4 lysine-20 specific
• NR-binding SET domain containing protein
• NSD1_HUMAN
• nuclear receptor-binding Su-var, Enhancer of zeste and Trithorax domain protein 1
• SOTOS1

Genomic Location

Sotos syndrome is reported to occur in 1 in 10,000 to 14,000 newborns. Because many of the features of Sotos syndrome can be attributed to other conditions, many cases of this disorder are likely not properly diagnosed, so the true incidence may be closer to 1 in 5,000.