Frequently Asked Questions
Following are some frequent questions regarding chromosome 15q duplication syndrome. If you have a question that is not addressed here, we invite you to send an email to email@example.com.
What is Chromosome 15q Duplication Syndrome?
Chromosome 15q duplication syndrome (dup15q) is a clinically identifiable syndrome which results from duplications of chromosome 15q11-13. These duplications most commonly occur in one of two forms. These include an extra isodicentric 15 chromosome, abbreviated idic(15), or an interstitial duplication 15. When the extra genetic material comes from the paternal chromosome, a child may have normal development. However, when the duplicated material comes from the maternal chromosome, developmental problems are often the result. In most cases of chromosome 15q duplication syndrome, the chromosome duplication is not inherited, but occurred as a random event during the formation of reproductive cells (eggs and sperm).
What is Isodicentric 15?
Isodicentric 15, abbreviated idic15, is one of a group of genetic conditions known as chromosome abnormalities. People with idic15 are typically born with 47 chromosomes in each of their body cells, instead of the usual 46 found in most people. In people with idic15, the extra chromosome is made up of a piece of chromosome number 15 which has been duplicated end-to-end like a mirror image. It is the presence of this extra genetic material that is thought to account for the symptoms seen in some people with idic15. Occasionally, a person may have more than one extra idic15, resulting in 48 or 49 chromosomes in all or some of their cells.
What is the difference between idic15 and Inverted Duplication 15?
There is no difference. Over the years, genetics laboratories have used different terminology to describe the same finding. Both terms mean that there is an extra chromosome which is made up of a duplicated, inverted chromosome 15. Years ago, before one knew that the extra chromosome was a number 15, it and other extra chromosomes of unknown origin were simply called 'supernumerary markers'.
What is an Interstitial Duplication of 15q?
People born without an extra chromosome but who have a segment of duplicated material within chromosome 15 are said to have an interstitial duplication. Most often, the specific chromosomal section known as 15q11-13 has been duplicated. This is the same section that makes up the extra chromosome in idic15. For this reason, people with interstitial duplications of 15q and those with idic15 share similar characteristics. For both conditions, there is a wide range of severity from one person to the next; as a group however, people with interstitial duplication 15 tend to have milder symptoms than those with idic15.
What is mosaicism?
Some children and adults with chromosome 15q duplications are said to have 'mosaicism', meaning that their extra 15th chromosome is present in some, but not all, of their body cells. A child with a mosaic form of idic15 is conceived with the usual pattern of 46 chromosomes; but somewhere along the line, during those early cell divisions, one cell accidentally divides incorrectly and produces an extra, inverted 15th chromosome (idic15). All the subsequent cells that come from that one have an idic15 pattern, although cells produced prior to the idic15 error continue to produce cells with the usual 46 chromosome pattern. Chromosome studies on a person with mosaic idic15 show some cells with 'normal' chromosomes (from the original cell divisions) and some with idic15. Mosaicism occurs by chance in this and many other chromosomal disorders.
How did this happen? Was it something I did?
When first learning about a chromosomal condition in their child, parents often wonder about the cause. In most cases of chromosome 15q duplication syndrome, the chromosome duplication is not inherited, but occurred as a random event during the formation of reproductive cells (eggs and sperm). In an egg, it occurred while the mother was a fetus in her mother’s uterus. In sperm this occurs continuously from puberty through adult life. Parents have no control over this natural process. There are some cases where the chromosome 15q duplication has been passed through generations. A chromosome study of the parents of an affected individual can determine if the duplication is inherited or de novo.
Individuals with Chromosome 15q Duplication Syndrome are born to parents of every socioeconomic, racial, and ethnic background. There is no known link between Dup15q and environmental or lifestyle factors. In other words, there is nothing that parents did before or during pregnancy to cause their child to be born with the chromosome 15q duplication.
How are chromosome 15q duplications diagnosed?
The extra chromosome in people dup15q can be easily detected through a blood test called a chromosome study. An additional genetic test, called FISH (Fluorescence In Situ Hybridization), confirms the diagnosis by distinguishing an idic15 from other supernumerary marker chromosomes. Interstitial duplications of chromosome 15 can be more difficult to detect on a routine chromosome analysis but are clearly identifiable using a 15q FISH study. Families should always discuss the results of chromosome and FISH studies with a genetic counselor or other genetics professional to ensure accurate interpretation.
Are there any physical/health problems associated with chromosome 15q duplications?
- Hypotonia: Babies with Dup15q usually have hypotonia (poor muscle tone). They may appear 'floppy' and have difficulty sucking and feeding. Some parents report that their babies with Dup15q have an unusual, weak cry. Motor milestones such as rolling over, sitting up, and walking are significantly delayed. Older children and adults with hypotonia often tire easily. Hypotonia in Dup15q syndrome generally decreases with age and sometimes progresses to hypertonia (tight muscle tone), particularly in the lower legs.
- Growth: Growth is retarded in about 20 – 30% of individuals with dup15q.
- Other Abnormalities: Rarely, babies with Dup15q may be born with a cleft lip and/or palate or differences in the way their hearts, kidneys, or other body organs are formed. For this reason, it is important for newly diagnosed children with Dup15q to be carefully evaluated for the possibility of such structural differences. Check with your genetics specialist for specific recommendations.
- Seizure Disorders: Seizures represent an important medical feature of Dup15q syndrome. Over half of all people with idic15 will have at least one seizure. The majority of those will experience their first seizure before age 5, but seizure onset occurs up through puberty and young adulthood in this population. There are many different types of seizures experienced by individuals with Dup15q. Children can start with one seizure type and other seizure types may emerge as the child ages. Response to treatment is variable. Some seizures are easily controlled with the first medication, other seizures are controlled for a while and then become more complex, and some children experience intractable seizures that have never been controlled with medication.
- Attention Deficit Disorders: Attention Deficit Disorder/Hyperactivity has been reported in a number of cases of children with Dup15q.
- Anxiety Disorders: Parent report of anxiety disorders in children with Dup15q has been noted on the Dup15q Alliance online community. More research in this area is needed.
- Other Medical Problems: Other reported medical problems included recurrent respiratory infections in childhood, middle ear effusions requiring tubes, eczema, precocious puberty, other menstrual irregularities, overeating and weight gain. Scoliosis is also reported in adolescence.
What is the chance of having a second child with a chromosome 15q duplication?
The answer to this question depends primarily on the results of chromosome and/or FISH studies in the parents of the child with the chromosome 15q duplication. Usually, Dup15q occurs in a child 'out of the blue', with no previous family history of the condition. Most often, genetic blood tests on the child's parents do not show any unusual arrangement of their chromosomes which would have predisposed them to having a child with Dup15q. In such cases, the occurrence of Dup15q is considered to be 'sporadic', and the child's parents are not at increased risk over anyone else in the general population for having a second child with Dup15q.
Occasionally, a parent of a child with a chromosome 15q duplication is found to have a rearrangement or other difference in one of his or her number 15 chromosomes. Although the parent is not affected by Dup15q, the presence of an unusual chromosome 15 pattern predisposes him or her to conceiving children a chromosome 15q duplication. For such parents, there is an increased chance of having a second child with Dup15q. There is also a possibility that other members of the parent's extended family could carry the same predisposing chromosome rearrangement. Chromosome studies are recommended for parents of all children with Dup15q to help identify those with an increased chance for recurrence. Each family is unique, and questions about recurrence should be discussed with a genetic counselor or other genetics specialist.
Is there a cure?
At the present time, there is no specific treatment which can undo the genetic pattern seen in people with Chromosome 15q Duplication Syndrome. The extra chromosomal material in those affected was present at or shortly after conception, and its effects on brain development began taking place long before the child was born. Although the fundamental genetic difference cannot be reversed, therapies are available to help address many of the symptoms associated with Dup15q. Physical, occupational and speech therapies along with special education techniques can stimulate individuals with Chromosome 15q Duplication Syndrome to develop to their full potential.
Brenda Finucane, MS, CGC, Genetic Services at Elwyn, Elwyn, PA contributed information to this FAQ.