What causes 18q-Syndrome?
18q-syndrome results from a deletion of part of chromosome 18. However, the size of the deletion is not consistent, and so varying numbers of genes can be lost (up to 500). In addition, in some cases, it appears that only some of the cells in the body carry the deletion. Both of these factors can lead to large differences in the severity and symptoms of 18q-syndrome.
For the most part, 18q-syndrome appears to arise spontaneously, meaning that it is not passed from parent to child. Therefore, having one child with 18q-syndrome does not necessarily increase the likelihood that a second child will have the disorder. However, there have been a few cases of familial 18q-syndrome described, where the disorder appeared to be inherited.
No direct connection to a single gene in the deletion of chromosome 18 has been made for all the symptoms of 18q-syndrome. Again, because several genes may be lost, it is possible that different symptoms result from the loss of different genes. Many scientists have suggested that the leukodystrophy manifestations of the disorder (reduced white matter of the central nervous system) is a result of the loss of a gene called Myelin Basic Protein (MBP). The protein produced from this gene is present exclusively in oligodendrocytes, which are the cells of the central nervous system that produce myelin. Loss of MBP in mice results abnormalities in myelin formation, supporting the theory that the loss of MBP is at least partly responsible for the leukodystrophy.
What are the symptoms of 18q-Syndrome?
As with many of the leukodystrophies, the symptoms of 18q-syndrome can vary dramatically from case to case; some are only mildly affected, while others are severely affected. Some symptoms that might be encountered include:
- Mental retardation (IQ<70)
- Developmental delay
- Growth deficiency: short stature
- Craniofacial dysmorphism: refers to an abnormality of the face and/or the head. Craniofacial dysmorphism can include abnormal growth patterns of the face or skull, and may involve the soft tissue as well as the bones. In the case of 18q-syndrome, craniofacial abnormalities will most likely include deep-set eyes, a “carp-shaped” mouth, microcephaly (small head), prominent ears, and midfacial hypoplasia (underdeveloped midfacial regions).
- Limb anomalies (including clubfoot, short thumbs)
- Eye movement disorders
- Genital hypoplasia: incomplete development of the genitals
- Hypotonia: poor muscle tone
- Hearing impairment
- Heart disease
- Skin manifestations
- Behavioral Problems: might include hyperactivity, aggressive behavior, tantrums
- Seizures: sudden episodes of electrical activity in the brain
- Microcephaly: small head
How is 18q-Syndrome diagnosed?
The most effective way of diagnosing 18q-syndrome is through a genetic analysis. A method known as Fluorescent In Situ Hybridization (FISH) is commonly used. FISH is a way of visualizing the chromosomes (DNA) of the patient, and allows physicians to see if there is any part of the chromosome that is missing.
The condition may also be partly diagnosed using Magnetic Resonance Imaging (MRI; please see our fact sheet on the MRI for more information). This can provide the physician with information regarding the severity of the myelin defect, though does not on its own define 18q-syndrome.
How is 18q-Syndrome treated?
Surgery can correct some of the craniofacial abnormalities often present in 18q-syndrome. Beyond this, treatment of 18q-syndrome is supportive, and can alleviate some of the symptoms of the disease. Prognosis is highly varied.
Is there prenatal testing for 18q-Syndrome?
18q-Syndrome only appears in approximately 1 in every 40,000 births. However, if testing is indicated, a test can be performed following amniocentesis in order to determine if there is a deletion of part of chromosome 18. However, it should be noted that 18q-Syndrome is not generally a disorder that is passed from parent to child, so the presence of 18q-Syndrome in a family member may not be indicative of the relative risk of a child having 18q-Syndrome.
How is research on 18q-Syndrome progressing towards better treatment and care for patients?
Many scientists are attempting to identify a correlation between genes that are part of the deletion in 18q-Syndrome and the symptoms seen. As scientists study the genes in the deleted region in more detail, they may learn more about the function of these genes. This knowledge could give scientists ideas regarding how to improve treatment or diagnosis.
What are the other names for 18q-Syndrome?
- Chromosome 18q- Syndrome
- Chromosome 18 Long Arm Deletion Syndrome
- Chromosome 18, Monosomy 18Q
- Monosomy 18q Syndrome
- Del(18q) Syndrome
- 18q Deletion Syndrome
- De Grouchy Syndrome