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Dup15q Syndrome
What is dup15q syndrome?
Dup15q syndrome (also called 15q11.2-13.1 duplication syndrome) is a disorder that results from the duplication of a portion of chromosome 15 (15q11.2-13.1). In healthy people, there is no extra copy of this part of chromosome 15, but in people with dup15q syndrome, the duplication, or doubling, of this specific segment often results in delays in development, decreased muscle tone (hypotonia), intellectual challenges, autism spectrum disorder (ASD) and epilepsy.
There can be one or two extra copies of this segment of chromosome 15 in people with dup15q syndrome. The more common type of duplication (60%–80% of cases) is called isodicentric (or “idic”), where the person has a small extra chromosome with two extra copies of the segment. The other type (20%–40% of cases) is called interstitial, where the person has one extra copy inside an already existing chromosome (see figure).
The prevalence of the disorder in the general population is estimated to be about 1 in 14,000 people, and dup15q syndrome is one of the most common chromosomal abnormalities in people with ASD, affecting around 1 in 500 people with autism.
What are the symptoms of dup15q syndrome?
Not everyone with these symptoms will have dup15q syndrome. They may be caused by other more common conditions. But if you or your child have any symptoms, it is important to get them checked by your doctor.
People with interstitial duplication usually have milder symptoms than people with isodicentric chromosome 15. The most common symptoms of dup15q syndrome include:
- Low muscle tone (hypotonia)
- Wide-based, clumsy gate (ataxic gate)
- Delays in development of motor skills (including sitting or walking)
- Moderate or occasionally severe intellectual disability
- Underdeveloped speech and language skills
- Difficulties with social interaction (similarly to children with ASD)
- Epileptic episodes with multiple types of seizure occurring in about half of people with dup15q syndrome
- Unusual facial features, including flattened nasal bridge and upturned nose
- Hyperactivity, emotional instability.
In some teenagers and young adults with epilepsy, sudden unexpected death in epilepsy (SUDEP) can occur.
What causes dup15q syndrome?
Dup15q syndrome is caused by the duplication of a segment of chromosome 15 (15q11.2-13.1). In every cell of the body, there are 46 chromosomes, and the mother and the father each give 23 chromosomes to their children. A tiny segment of chromosome 15 coming from the mother is duplicated in the disorder causing the symptoms described above.
There are two main mechanisms for the duplication to happen:
- Isodicentric chromosome 15: a small extra chromosome (supernumerary chromosome) results in two extra copies of the segment. That means that instead of the normal two copies, there will be four copies of the 15q11.2-13.1 segment (called tetrasomy).
- Interstitial duplication 15: the duplication results in one extra copy of the segment. That means that three copies of the 15q11.2-13.1 segment will be present (called trisomy).
Although there are several important genes in this segment, no single gene has been identified whose duplication would cause dup15q syndrome on its own. However, the extra copies of the gene segments contain extra amounts of certain genes involved in development, which might disrupt normal development. This disruption leads to the characteristics of the disorder.
Understanding what causes dup15q syndrome will help researchers find more effective ways to treat it.
Figure 1
A. Schematic of the normal paternal and maternal chromosome 15
B. & C. The most common causes of maternal dup15q:
— B. Interstitial duplication of 15q11.2-13.1
— C. Isodicentric triplication of 15q11.2-13.1
Learn more about Dup15q syndrome
How is dup15q syndrome diagnosed?
If your doctor thinks you might have dup15q syndrome, they will look for at least one extra copy of the 15q11.2-13.1 region of chromosome 15.
The following genomic testing methods can be used to diagnose dup15q:
- Chromosomal microarray analysis: detects the number of copies of a specific region on the chromosome. This helps to determine any deleted or extra genetic material (like a duplication of a segment of the DNA).
- Targeted duplication analysis: different methods are available depending on how big the duplication of the DNA segment is. This can be used to test relatives of someone who has 15q11.2-13.1 duplication.
- FISH (fluorescence in situ hybridization): used to determine if the duplication of the 15q11.2-13.1 portion is due to an extra chromosome (supernumerary) or an interstitial duplication.
Prenatal testing is also available to detect the 15q interstitial duplication, however it cannot reliably predict how severe the disease will be in an affected child. All families with a child diagnosed with dup15q syndrome should be referred for genetic counselling.
What treatment options are available for dup15q syndrome?
At the moment, there is no disease-modifying treatment for dup15q syndrome, so treatments are used to relieve symptoms in order to improve quality of life. In many cases, there is a need for ongoing specialist care. A multidisciplinary team can evaluate the speech and motor development levels of children and refer them to the appropriate educational programs. Supportive care includes:
- Occupational therapy
- Physical therapy
- Alternative and augmentative communication (such as tablets with pictures)
- Behavioural therapy
- Standard management for seizures
In the case of acute changes in behaviour, careful physical examination is necessary (the reason for the behavioural change might be physical pain or discomfort).
What is the outlook for a person with dup15q syndrome?
Clinical trials are designed to look at how safe experimental drugs or procedures (such as new types of surgery) are and how well they work. Researchers are working hard to learn more about dup15q syndrome. Ongoing trials are testing new medicines to find a way to positively impact the development of children with dup15q. Additionally, finding the answers to questions like which genes in the 15q11.2-13.1 region lead to the syndrome or which genes cause which features will also lead to a better understanding of dup15q syndrome.
If you would like to know more about Roche sponsored clinical trials or are interested in taking part in a clinical trial, speak to your doctor or visit the Roche ForPatients clinical trials page link
References
National Organization for Rare Disorders (NORD). Dup15q syndrome. Accessed 23 January 2023. Available from: Link
MedlinePlus. 15q11-q13 duplication syndrome. Accessed 23 January 2023. Available from: Link
GeneReviews. Maternal 15q duplication syndrome. Accessed 23 January 2023. Available from: Link
Dup15q Alliance. Signs, symptoms and characteristics. Accessed 23 January 2023. Available from: Link
Dup15q Alliance. Diagnosing dup15q syndrome. Accessed 23 January 2023. Available from: Link
ForPatients. Dup15q syndrome. Accessed 23 January 2023. Available from: Link
ClinicalTrials.gov. A clinical study evaluating the efficacy and safety of retinoic acid in patients with 15q11-q13 duplication syndrome. Accessed 23 January 2023. Available from: Link
LaSalle JM, Reiter LT, and Chamberlain SJ. Epigenetic regulation of UBE3A and roles in human neurodevelopmental disorders. Epigenomics. 2015 Oct;7(7):1213-1228. Available from: Link
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