When asked about thyroid testing, several parents reported that their children had not been tested or that they did not know if they had been tested. Given that thyroid problems are detected more often in people with DS than in the general population, it is recommended that individuals with non-Mosaic DS be screened yearly. This is particularly important, since thyroid problems can be treated. Three individuals in this group were reported to have hypothyroidism. This suggests that children having Mosaic DS also have an increased risk for thyroid problems and should also consider having annual testing.
When asked about their children's health, there were a few conditions that a great number of families mentioned. Most of these were related to the respiratory tract or ears. The most commonly mentioned health problems were recurrent ear infections (or fluid in the middle ears) and common colds or upper respiratory tract infections (URI's). Respiratory infections affected the nasal passages, throat, and lungs. Also mentioned were asthma, allergies, bronchitis, pneumonia, sinus infections, and blocked tear ducts.
Many children and adults with Mosaic DS had surgeries for the health conditions that they were either born with or acquired. About 56% (25/45) had one or more surgeries (tubes to drain middle ear, corrective eye wear or other surgeries, not including placement of tubes in ears). The most common procedure was the placement of tubes in the ears to drain fluid (myringotomy). Tonsillectomies and procedures to open blocked tears ducts (lacrimal ducts) were also common. A few individuals had surgery to correct strabismus, a condition where both eyes do not move together and appear crossed.
Another health-related issue in DS is excessive weight gain, which is reported to occur in about 25% of individuals with full DS. This usually occurs around the time of puberty. Excessive weight gain (starting between ages six and 27) was reported for five cases. Given the relatively young ages of members of the group, additional individuals may experience weight gain later in life. Several families noted that they tried to establish good eating and exercise patterns to prevent gain. In describing strategies to control weight, common themes were education and supervision. Specifically, parents described teaching their children to reduce fats and eat healthy foods, supervising food access, limiting snacks, and encouraging exercise.
Almost all (43/45) of the individuals with Mosaic DS started their formal learning processes in early intervention programs. One of those who did not was in the older range and early intervention had not been available when she was an infant or toddler. In early intervention, adults and babies interact in a specialized way meant to enhance the infant's development and help him/her learn new skills. Of those having early intervention, the majority used public programs, while the remainder used private ones. Public programs were usually run by the county or state. Some programs were provided through agencies like the United Way or through state universities.
Parents reported that most intervention programs provided OT, PT, and speech therapy. Often, group play or play therapy was also a component. Some also included parent support groups, social work services, case management, or special help in obtaining services or assistive devices from other agencies. Programs were offered in a wide variety of settings, including center-based, home-based, and combination programs.
Much like early intervention, of those who were school age or older (30 individuals), the majority attended public school programs. Programs varied between individuals and addressed special needs in different ways. Some were involved fully in special education programs. One child was in a regular elementary classroom with no special help. The majority, however, fell somewhere between these two ends of the spectrum, with combination programs. Many were included with their peers for certain subjects, such as social studies or art, and went to a resource room for other subjects, such as reading or math. Many families also described that their children's education programs had adjusted over time. For example, a child may have started in a special education classroom, then progressed to situations with increasing inclusion.
Eighteen of the 30 children school-age or older had been involved in inclusion programs at some point during their educations (primarily through public school). Ten families reported that their children had been involved in full inclusion with varying levels of support. States in which inclusion appeared to be available to these families included Georgia, Illinois, Louisiana, Maryland, Massachusetts, Michigan, Montana, New Jersey, New York, North Carolina, Ohio, Puerto Rico, South Carolina and Virginia.
One way to explore what differences may exist between conditions like Mosaic and non-Mosaic DS is to identify a group of individuals with each condition who are otherwise very similar. The more similar the two groups are in other ways, the easier it becomes to decide what differences may be due to the Mosaicism. As you may imagine, putting together these groups can be difficult. We were able to match 28 of the 45 individuals with Mosaicism in this study by sex and age with individuals having full DS, creating two groups. Once the 28 pairs were matched, we also found that the family incomes and education levels of the parents were similar between the two groups.
We then compared the two groups for three major categories. First, we wanted to compare how parents rated their children for having certain traits, such as low muscle tone or hearing loss. Secondly, we wanted to compare when children in the groups reached milestones of development. Finally, we wanted to compare services the two groups were receiving.
We did not find statistically significant differences in how parents described traits of their children with Mosaic or non-Mosaic DS. This was somewhat surprising because many parents we have spoken with described their children with Mosaicism as appearing "mild" or having few features of DS. There are several reasons why real differences may be difficult to identify. First, it is difficult to detect differences between small groups. Second, several of the traits we asked parents about may be challenging to answer with “yes” or "no." For example, although two children may both have low muscle tone, one child's low tone may be much more severe than the other's. We are continuing these studies with physician evaluations of some of these traits. It is hoped that the additional studies will provide further insight about this question.
We found a more meaningful trend when we looked at development in the two groups, as reported by parents. With the exception of speech, there was a trend toward individuals with Mosaic DS reaching the milestone evaluated at an earlier age. However, a clear difference (identified by statistical testing) was apparent only for crawling and walking. The trend that we see suggests that further research needs to be done to examine possible differences.
Finally, we found no significant differences between the two groups when parents were asked about services they used. Services that we asked about included PT, OT, speech therapy, early intervention, sign language training, school programs, vocational training, camps, and respite care. This suggests that although it is still unclear if differences exist between Mosaic and non-Mosaic DS, families and individuals with Mosaicism have resources available that are similar to those for full DS and appear to be using them.
In speaking with families, we found that one of the greatest frustrations they described was not knowing what Mosaicism means for their children or what to expect. Through our study we have begun to address these questions, and our results have helped give us and other investigators direction for further study. Also, we are currently exploring how the percentages of Mosaicism in individuals may influence their rates of development. Preliminary studies suggest that a relationship between these variables may exist, but further investigation is needed to obtain a clearer understanding.
We learned that people with Mosaic DS keep busy! Members of our group were involved in a number of sports, groups, and organizations, and also enjoy spending time with their families.
Sixteen members of the group had attended some type of summer or day camp. A variety of camps were described, including public camps, camps for children with special needs, religious camps, and even a specialized "speech camp." One woman with Mosaic DS, currently in her thirties, enjoyed her camp experience so much that she now goes back and serves as a volunteer assistant counselor.
There were three men and one woman in our study group over the age of 18. Their parents described the levels of independence they developed as young adults and their involvements in the community.
All four of the young adults were described as having achieved helpful living skills, such as telling time and doing basic reading, writing, and math (adding and subtracting). It is important to note that each individual's skills varied within these categories. Two of the group used public transportation, such as the bus or train. One started to do so at age 16 and the other at 19. Each individual had his/her own experiences in working and volunteering in the community.
One young man, age 29, began working when he was 19. He worked four years as a courtesy clerk in a grocery store, and his responsibilities included bagging groceries and collecting carts. At age 27, he stopped working for a salary, but started a volunteer program. He currently volunteers in a local hospital laundry facility, stacking and folding garments. In his free time he enjoys being part of a local acting group and performs plays and musicals.
In the cold winter climate of his home, a second young man's household chores include both shoveling snow and using the snow blower. At age 18, he became employed at K-Mart. His duties include putting tags on apparel, bagging items, and greeting customers as they enter the store.
The third young man, age 24, began working at 14 years of age. His most recent work involves folding boxes for medical sharp waste and dismantling pallets in a warehouse. At age 19, he moved into a group home that is only a 20-minute car ride from his family. His parents report that he "loves his job" and works about 40 hours weekly. He often spends his weekends at home and enjoys taking short trips with his parents to visit relatives and friends.
Finally, a young woman, currently age 32, graduated from high school with a modified diploma in 1982. She received work-training in several settings, including school and a program at a local university, and has held several jobs, including employment at a preschool and restaurant. Participating in the Special Olympics and following television and movie stars are included in her hobbies.
This informational booklet was created in response to a large number of families describing a lack of available resources specifically discussing Mosaic DS. Several parents commented that there are many excellent resources about DS in general, but few of them contain more than a sentence or two about Mosaicism. We asked families to identify the resources that they have used most often to learn about Mosaicism and DS in general.
We also asked them to rank the top three sources of information that they used (with number one being the most used and three the least) from the following choices:
* medical geneticist
* other medical doctor
* genetic counselor
* other health professional
* social worker
* national support group/DS organization
* local support group/DS organization
* medical books/ journals/ resources
* other books/ journals/ resources
As a group, families ranked their pediatricians, national support groups or DS organizations, and other books/journals/resources as the three resources most often used. Several parents chose "other" as one of their choices and offered suggestions of additional resources. These included teachers, therapists, daycare providers, the Internet, DS clinics, and perhaps most importantly, other parents of children with DS.
After having a child with any genetic condition or health problem, some families are interested in exploring the chance of having another child with the same condition. The chance typically given for having another child with DS is about I%, or a I in 100 chance.
In families in whom a child with DS (without Mosaicism) was born, it is expected that almost all of the cases were due to an extra chromosome 21 in the sperm or egg. This suggests that for the portion of cases of Mosaic DS where the first change occurred in the sperm or egg, the recurrence estimate of about 1% should also apply. It is not clear if this is the best estimate for families in whom Mosaic DS occurred after conception. Although about 1% is currently the best estimate, their chance may be lower than this.
During future pregnancies, some families may wish to learn in advance if the developing baby will have a type of DS. There are several testing options for families in this situation. Some of these tests are diagnostic tests (directly look at the baby's chromosomes). Others are called screening tests. These tests help predict the chance that the baby may have a problem. There are two types of diagnostic tests that can be done during pregnancy to look at the baby's chromosomes: (1) chorionic villus sampling, or CVS, and (2) amniocentesis.
In both CVS and amniocentesis, doctors are careful to use clean, sterile procedures and to check the baby while the test is being done. Both tests are typically done with ultrasound guidance. This means that while the test is being done, ultrasound is used to show an image of where the baby is and how it is responding to the test. However, there is still a risk of miscarriage for both CVS and amniocentesis. This risk is typically quoted as about 1% (1/100) for CVS and 1/2% (1/200) for amniocentesis. The two tests are also done at different times during pregnancy. CVS is usually done around the tenth week of pregnancy, while amniocentesis is usually done later, typically during weeks 14-18 of pregnancy. As you may imagine, deciding to have this type of prenatal testing is a personal choice for each family. This decision can be especially difficult due to the chance of miscarriage associated with these procedures. There are other screening tests that are less accurate, but do not have significant risks associated with them.
One of these screening tests is done by looking at certain proteins in a pregnant woman's blood (maternal serumscreening). Depending on how many proteins are checked, this can be called an MSAFP (maternal serum alpha fetoprotein) test, a double screen, or a triple screen. The test is done early in the second trimester of pregnancy. Based on the levels of different proteins, the mother's age, and additional factors (such as the week of pregnancy), the chance of having a baby with DS or another chromosome problem is estimated. If this chance is greater than or about equal to the risk of amniocentesis, the pregnant woman will be offered this procedure. The risk associated with the screening test is only that of having blood drawn (which can rarely lead to effects such as infection). However, the maternal serum test is not a diagnostic test and does not directly evaluate the baby's chromosomes.
A second type of test that has no known risk is a detailed ultrasound, sometimes called a fetal scan. This type of ultrasound is typically done around week 20 of pregnancy. In this type of ultrasound, the baby's organs, such as the heart, kidneys, and brain, are examined closely. Ultrasound can find many changes in structure, such as some heart defects. However, it cannot tell whether a birth defect is caused by a chromosomal change. Also, it is possible for no changes to be found on ultrasound and for the baby to still have a chromosomal condition. If a change is found through ultrasound, some families may then decide to have an amniocentesis.
If you are considering pregnancy or are pregnant, you can ask your doctor for more information about these testing options. Most women have the opportunity to discuss the details of testing with a genetic counselor, nurse, or doctor before the test is done. In addition, follow-up counseling and support is available to families who are found to have an increased chance for having a baby with a problem or who are given the diagnosis of a chromosomal condition in the developing baby.
We asked the parents in our study what they felt were the most important things to tell new parents of children with Mosaic DS. Here are some of their responses.
"These kids are very loving and easy going children. They have been developmentally delayed, but are ever so willing to learn and can progress along very well."
"He or she will just be a little slower to catch on in a lot of areas. He or she will bring a lot of joy and fun to your life that a lot of people will not experience."
"The world seems pretty bleak when you first learn the diagnosis, but it isn't nearly as bad as it seems at that moment...As time goes on, you'll understand that 'Life Goes On' just as if the child is 'normal' with a few extra corners to go around."
"I can't honestly say that her having Mosaic Down Syndrome is apparent at all. I would say what I would say about DS period: Your child will give you more happiness than you can imagine right now. I have learned so much from my children with DS."
"Be consistent, keep your expectations the same as with any other child."
"There is a wide range of how a child may be affected. Be optimistic and hope for the best."
"Our kids are children first--treat them as you would any other child until something occurs that you need to treat or deal with differently. Expose them to everything, give them a chance to succeed or fail."
Mosaic Down Syndrome
Frequently Asked Questions
The Medical Maze: What is Mosaic Down Syndrome?
by Carol Strom, M.S.
A: Children with mosaic Down syndrome have two distinct cell groupings. In some cells there is a total of 46 chromosomes, which is the “typical” group. In other cells there is an extra copy of the chromosome #21, making 47 cells total for this group.
Q: How does mosaic Down syndrome happen?
A: Ordinarily, when an egg and a sperm are joined at conception, a single cell is created with a total of 46 chromosomes. These chromosomes are copied, the copies are separated, and the cell then divides to create two identical “daughter” cells. The chromosomes in these two cells are copied, the copies divide and four cells are created. These four cells become eight cells. Eight cells become 16 cells, and so on.
If nothing disrupts the chromosome replication and separation process, each cell in the body should have the same number of chromosomes that were present in the fertilized egg. However, errors can occur in this replication and separation process.
Two mechanisms have been proposed to explain why a child may be born with mosaic Down syndrome. The most likely explanation is that an extra copy of chromosome #21 was present in the egg or the sperm at the time of conception. However, shortly after conception, an error occurred in the chromosome replication and separation process, and the extra copy of the chromosome #21 was not passed on to both cells. In this way, a second cell grouping was created with only 46 chromosomes.
If this error in the chromosome replication and separation process occurred at the 4 cell stage, 1/4 of the cells would have 46 chromosomes and 3/4 would have 47 chromosomes. If the error occurred at the 8 cell stage, 1/8 of the resulting cells would have 46 chromosomes and 7/8 would have 47.
It is also possible that a child with mosaic Down syndrome inherited a total of 46 chromosomes at the time of conception. If this were the case, then the error in chromosomal separation, which resulted in the formation of a second cell grouping with an extra chromosome #21, occurred early in the baby’s development.
Q: How does it effect her development?
A: Every child is born with a unique set of talents and abilities. However, it is impossible to predict what these talents and abilities will be. This is true for a child who inherits 46 chromosomes. This is true for a child with trisomy 21 (Down syndrome), and this is true for a child with mosaic Down syndrome.
While it is impossible to tell you what the future holds for your daughter, I can share with you information about other children with mosaic Down syndrome. Studies have shown that individuals with mosaic Down syndrome, on average have IQ scores that are 10-30 points higher than individuals with trisomy 21. Their scores are thought to be higher because the presence of the cells with 46 chromosomes modify the effects of the cells with 47 chromosomes.
Q: Is it possible to predict a child’s IQ based on the number of normal cells present in the study?
A: In most cases chromosome studies are done using white blood cells. The number of blood cells containing 46 chromosomes may not accurately reflect the number of skin cells, heart cells, or brain cells with 46 chromosomes. Therefore, it is impossible to predict what affect, if any, the presence of these chromosomally normal cells will have on a child’s development.
The parents of children with mosaic Down syndrome are like the parents of any other child. Your child’s strengths and weaknesses will only be revealed over time.
Fishler K, and Koch R. Mental Development in Down syndrome mosaicism. American Journal of Mental Retardation 1991; 96 (3): 345-351.
Carol Strom, M. S. is a genetic counselor and advocate for families and individuals with disabilities at the University of South Dakota School of Medicine in Rapid City. She welcomes any questions you may have regarding genetic issues. You may send your questions for her to Disability Solutions.
More FAQ's on Mosaic Down Syndrome
by Dr. Len Leshin, MD, FAAP
Copyright 1999, All rights reserved
What is Mosaicism?
Every cell in the human body comes from one initial cell: the fertilized egg, which is also called the zygote. After fertilization, the zygote then proceeds to divide. As new cells form, the chromosomes duplicate themselves so that the resulting cells have the same number of chromosomes as the original cell. However, mistakes sometimes happen and one cell ends up with a different number of chromosomes. From then on, all cells originating from that cell will have the different chromosomal number, unless another mistake happens. (All like cells originating from a single type of cell is called a cell line; for example, the skin cell line, the blood cell line, the brain cell line, etc.)
When a person has more than one type of chromosomal makeup, that is called mosaicism, like the mosaic style of art in which a picture is made up of different colors of tiles. In Down syndrome, mosaicism means that some cells of the body have trisomy 21, and some have the typical number of chromosomes.
How is Mosaicism Diagnosed?
The usual way in which mosaic Down syndrome is discovered is through genetic testing of the baby's blood. Typically, 20 to 25 cells are examined. If some of the cells have trisomy 21 and some don't, then the diagnosis of mosaicism is made. However, this blood test can only determine the level of mosaicism in the blood cell line.
While mosaicism can occur in just one cell line (some blood cells have trisomy 21 and the rest don't), it can also occur across cell lines (skin cells may have trisomy 21 while other cell lines don't). In the latter case, it may be more difficult to diagnose mosaicism. When mosaicism is suspected but not confirmed through the blood test, other cell types may be tested: skin and bone marrow are most commonly the next cells checked. Because skin cells and brain cells arise from the same type of cell at the beginning of fetal development (ectoderm), many doctors believe that skin cell tests reflect the chromosomal makeup of the brain cells as well.
How Does Mosaicism Happen in Down Syndrome?
There are two different ways mosaicism can occur:
- The initial zygote had three 21st chromosomes, which normally would result in simple trisomy 21, but during the course of cell division one or more cell lines lost one of the 21st chromosomes. Here's a diagram of this method.
- The initial zygote had two 21st chromosomes, but during the course of cell division one of the 21st chromosomes were duplicated. Here's a diagram of this method.
It's possible to determine the origin of mosaicism in individual cases using special DNA markers, but this isn't done on a regular basis.
What Does Mosaicism Mean for my Child?
At the present time, there is not much research on the similarities and differences between simple trisomy 21 and mosaic trisomy 21. One report published in 1991 on mental development in Down syndrome mosaicism compared 30 children with mosaic Down syndrome with 30 children with typical Down syndrome. IQ testing showed that the mean IQ of the mosaic group was 12 points higher than the mean of the non-mosaic group. However, some children with typical Down syndrome did score higher on the IQ tests than some of the children with mosaic Down syndrome.
The Department of Human Genetics at the Medical College of Virginia has had an ongoing study project of children with mosaic DS. In a survey of 45 children with mosaicism, they found that these children did show delayed development compared to their siblings. When 28 of these children with mosaicism were matched up with 28 children with typical Down syndrome for age and gender, the children with mosaicism reached certain motor milestones earlier than children with typical DS, such as crawling and walking alone. However, the speech development was equally delayed in both groups.
The Department of Human Genetics at the Medical College of Virginia/Virginia Commonwealth University has a very nice booklet on this topic that is available free of charge. Contact Dr. Colleen Jackson-Cook or Lauren Vanner at:
Dept of Human Genetics
Virginia Commonwealth University
Richmond, VA 23298-0033
1. Understanding the mechanism(s) of mosaic trisomy 21, by using DNA polymorphism analysis. Pangalos C et al. Am. J. Hum. Genet. 54:473-481, 1994.
2. Mental Development in Down Syndrome Mosaicism. Fishler K and Koch R. Am. J. Mental Retardation 96(3):345-351, 1991.
3. Medical Care in Down Syndrome, Rogers PT and Coleman M, Marcel Dekker, NY, 1992; p14-16.