Mosaic Down Syndrome: Symptoms, Diagnosis, And Outlook

Genetic conditions can cause unique physical, cognitive, and emotional differences that may impact how an individual navigates the world. One such condition is mosaic Down syndrome, a rare subtype of Down syndrome. Understanding this condition can be beneficial when confronting support options unique to the subtype. 

What is mosaic Down syndrome? Extra copy of chromosome 21

Down syndrome is a genetic condition in which a person is born with an extra chromosome. Specifically, they have an additional copy of chromosome 21, which is why the condition is sometimes called trisomy 21. This extra copy of chromosome impacts brain and body development and causes mental and physical challenges. There are three primary risk factors for having a child with this genetic disorder: the mother's age, being a genetic carrier, and already having one child with the condition.

Mix of cells and copies of chromosome

Mosaic Down syndrome is rare in Down syndrome cases, affecting only about 2% of the 6,000 babies born with Down syndrome every year. While children with Down syndrome have three copies of chromosome 21 in every cell, those with mosaic Down syndrome have a mix of cells. Some have three copies of this chromosome, while other cells have two. Depending on how many cells are affected and where they are in the body, a child with mosaic Down syndrome may have the same features as one with Down syndrome. However, because some of the body’s cells have the typical two chromosomes, they may have very mild features or fewer characteristics of the condition.

Diagnosing mosaic Down syndrome

Screening blood tests and ultrasounds can determine whether a pregnancy has a higher or lower chance of having Down syndrome, but these tests are generally not conclusive. These screening tests rarely give an abnormal result if the baby is healthy, but they can give false negatives. Other diagnostic tests may be more reliable but have higher risks for both the pregnant parent and the fetus as they are invasive and require collecting amniotic fluid or samples from the placenta or umbilical cord.

Mosaic diagnosis: Mixture of cells and copies of chromosome 

When a baby with Down syndrome is born, doctors perform blood tests for chromosomal studies. These lab tests determine whether the blood sample contains a mixture of cells with 46 and 47 chromosomes. If it does, a doctor can diagnose mosaic Down syndrome.

A mosaic diagnosis is expressed as a percentage. Generally, these tests analyze 20 different genes. If 15 out of 20 cells have an extra chromosome, the baby has a level of mosaicism at 75%. If 10 out of 20 cells are affected, the level of mosaicism would be 50%. These percentages can also vary in different parts of the body. The level of mosaicism in the brain may be higher or lower than in the skin, muscle, or blood. Where the differences occur and how high the level of mosaicism is can determine the type and severity of symptoms. However, without a tissue biopsy, there is no way to determine which organ systems are affected in people with mosaic Down syndrome.

Mosaic Down syndrome symptoms

Symptoms of mosaic Down syndrome are the same as symptoms of Down syndrome, though they may be less severe. Physical symptoms can include the following:

• Decreased muscle tone
• Short neck with excess skin at the back
• Flattened nose and facial profile
• Small ears, mouth, and head
• Upward slanting eyes with prominent skin folds
• White spots in the iris
• Short, wide hands
• Short fingers

Mosaic Down syndrome symptoms in infants

Another result of these chromosome defects is that children with Down syndrome may develop more slowly. Infants with the condition may lift their heads or roll over slower and take longer to learn to sit up, stand, crawl, and walk. They may also have mild to moderate cognitive impairment, poor judgment, and a short attention span. Children with Down syndrome can experience delayed speech and language development. Although children often develop the skills to live a functional life, it can take them longer than other children.

Other conditions that can occur with mosaic Down syndrome

Children with any form of Down syndrome are also at higher risk for other health problems. For those with mosaic Down syndrome, the risks of developing these conditions may depend on the level of mosaicism and what cells are affected. Comorbid conditions include the following:  

• Heart anomalies, including congenital heart disease
• Vision problems, including cataracts, near-sightedness, and rapid involuntary eye movements
• Hearing loss
• Increased risk of infections 
• Hypothyroidism
• Blood disorders, including anemia and leukemia
• Spinal issues
• Disrupted sleep patterns and sleep disorders
• Epilepsy
• Gum disease and dental problems, including misaligned teeth and developing fewer teeth
• Digestive issues, including Celiac disease
• Mental health and emotional problems or mental illnesses, including ADHD, anxiety, depression, autism spectrum disorder (ASD), aggression, or social withdrawal

Management and treatment of mosaic Down syndrome

The American Academy of Pediatrics (AAP) lays out specific guidelines for the health supervision of children with Down syndrome, including the mosaic variant. Life-long management and monitoring are often beneficial. 

People with Down syndrome are screened regularly for various conditions, including hearing loss, sleep apnea, spinal cord injury, eye conditions, neurological dysfunction, and thyroid function. A cardiac specialist may closely follow those with heart involvement, and frequent appointments may be recommended. 

Higher risk of infection for people with Down syndrome

People with Down syndrome are often at a higher risk of infection. Infants and children can be taken to the doctor to check for signs of infection, as any illness can have significant side effects. For example, recurrent or severe ear infections can lead to hearing loss, and respiratory illnesses can exacerbate a heart condition. The AAP also recommends that children stay up-to-date on vaccines unless there are specific contraindications.

Behavioral and mental health issues may be carefully monitored as well. Research shows that those with Down syndrome are more likely to develop mood disorders and anxiety disorders, and getting proper treatment may improve their quality of life. 

Outlook for children with Down syndrome 

Parents or caregivers of children with mosaic Down syndrome may wonder how their child will grow up and evolve. Each person with mosaic Down syndrome is different, and it is impossible to predict how anyone’s life will turn out. Many people with this condition have the same goals and ambitions as others and can lead fulfilling lives with marriages, families, friends, and careers. 

As the International Mosaic Down Syndrome Association says, “It is important to remember that people do not die from having mosaic Down syndrome; they die because of medical complications surrounding this syndrome.” Parents should ensure their children get the medical care they need to help them stay healthy for as long as possible.

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Mental health support options for people with Down syndrome

Mental health can be a concern for people with Down syndrome and their primary caregivers. Research shows that parents of children with Down syndrome have reported high levels of anxiety, depression, and distress. Parents may benefit from talking to a therapist to help them manage these challenges. 

It may be challenging to access in-person therapy when living with a disability or caring for a child with unique needs. In these cases, online therapy can be a flexible, convenient option. With an online therapy platform like BetterHelp, clients can meet with a therapist at a time that suits their schedule, and they can change providers at any time until they find a fit. 

Studies also show that online therapy is as effective as in-person treatment, so both treatment approaches are valid options for people seeking mental health support. Online treatment can be effective and convenient for people who prefer an alternative to meeting with a therapist in person.