18q deletion syndrome
18q deletion syndrome is a chromosomal condition that results when a piece of chromosome 18 is missing. The condition can lead to a wide variety of signs and symptoms among affected individuals.
Most people with 18q deletion syndrome have intellectual disability and delayed development that can range from mild to severe, but some affected individuals have normal intelligence and development. Seizures, hyperactivity, aggression, and autistic behaviors that affect communication and social interaction may also occur. Some people with 18q deletion syndrome have a loss of tissue called white matter in the brain and spinal cord (leukodystrophy), structural abnormalities of the brain, or an abnormally small head size (microcephaly).
Other features that are common in 18q deletion syndrome include short stature, weak muscle tone (hypotonia), narrow auditory canals leading to hearing loss, and limb abnormalities such as foot deformities and thumbs that are positioned unusually close to the wrist. Some affected individuals have mild facial differences such as deep-set eyes, a flat or sunken appearance of the middle of the face (midface hypoplasia), a wide mouth, and prominent ears; these features are often not noticeable except in a detailed medical evaluation. Eye movement disorders and other vision problems, genital abnormalities, heart disease, and skin problems may also occur in this disorder.
18q deletion syndrome occurs in an estimated 1 in 40,000 newborns. This condition is found in people of all ethnic backgrounds.
18q deletion syndrome is caused by a deletion of genetic material from the long (q) arm of chromosome 18. This chromosomal change is written as 18q-. The size of the deletion and its location on the chromosome vary among affected individuals.
The signs and symptoms of 18q deletion syndrome, including the leukodystrophy that likely contributes to the neurological problems, are probably related to the loss of multiple genes on the long arm of chromosome 18. 18q deletion syndrome is often categorized into two types: individuals with deletions near the end of the long arm of chromosome 18 are said to have distal 18q deletion syndrome, and those with deletions in the part of the long arm near the center of chromosome 18 are said to have proximal 18q deletion syndrome. The signs and symptoms of these two types of the condition are overlapping, with certain features being more common in one form of the disorder than in the other. For example, hearing loss and heart abnormalities are more common in people with distal 18q deletion syndrome, while seizures occur more often in people with proximal 18q deletion syndrome. Researchers are working to determine how the loss of specific genes in these regions contributes to the various features of 18q deletion syndrome.
Most cases of 18q deletion syndrome are not inherited. The deletion occurs most often as a random event during the formation of reproductive cells (eggs or sperm) or in early fetal development. Affected people typically have no history of the disorder in their family.
In some cases, 18q deletion syndrome is inherited, usually from a mildly affected parent. The deletion can also be inherited from an unaffected parent who carries a chromosomal rearrangement called a balanced translocation, in which no genetic material is gained or lost. Individuals with a balanced translocation do not usually have any related health problems; however, the translocation can become unbalanced as it is passed to the next generation. Children who inherit an unbalanced translocation can have a chromosomal rearrangement with extra or missing genetic material. Individuals with 18q deletion syndrome who inherit an unbalanced translocation are missing genetic material from the long arm of chromosome 18, which results in the signs and symptoms of this disorder.
These resources address the diagnosis or management of 18q deletion syndrome:
These resources from MedlinePlus offer information about the diagnosis and management of various health conditions:
- 18q- syndrome
- chromosome 18 long arm deletion syndrome
- chromosome 18q deletion syndrome
- chromosome 18q monosomy
- chromosome 18q- syndrome
- De Grouchy syndrome
- del(18q) syndrome
- monosomy 18q
- Alexander Graham Bell Association for the Deaf and Hard of Hearing
- Chromosome 18 Registry and Research Society
- Chromosome Disorder Outreach
- March of Dimes: Chromosomal Conditions
- National Oganization for Rare Disorders
- The Arc: For People with Intellectual and Developmental Disabilities
- Unique: The Rare Chromosome Disorder Support Group
- United Leukodystrophy Foundation