Help Celebrate Trisomy 9 Awareness Day

By: Kelsey Hogan, Mindy Li, and Vera Shively

Just over a year ago, Illinois Governor JB Pritzker signed a Proclamation recognizing March as Trisomy Awareness Month and officially designated March 9th as Trisomy 9 Awareness Day. While individuals with trisomies and their families advocate year-round, this month is dedicated to increasing awareness, fostering research that may lead to treatments, and strengthening support for patients and families. Greater awareness leads to better resources, earlier diagnosis, and expanded research efforts—all of which can improve outcomes for those with trisomy disorders. 

Understanding trisomies, begins with a basic knowledge of our genetic makeup. Chromosomes, which carry our genetic instructions, play a key role in development and health. To better understand how trisomies occur, let's first look at the structure and function of our chromosomes.  

Our Bodies, Cells and Chromosomes 

Our bodies are made of trillions of cells, or building blocks. Within our cells, genetic material (DNA) is tightly packaged in structures called chromosomes. The DNA contains instructions for how our bodies grow, develop, and function properly. Each chromosome is a distinct unit that contains hundreds to thousands of genetic instructions. They are numbered using a standard notation so they can be studied and described in detail. Humans have 23 pairs of chromosomes; one of each pair is inherited from their biological mother and the other from their biological father, for a total of 46.  

Normal Human Karyotype (46, XX or XY)                             Karyotype with Trisomy 9 (47,XX or XY,+9)  

Variants are changes in our genetic material 

In simple terms, variants are changes in our genetic material. Some are inherited and harmless, while others occur spontaneously. These variants can contribute to genetic diversity, but some can impact development and health. Because the human genome is complex, there are many types of variants, with different locations, sizes, and effects on health and development. 

The study of chromosomes is called cytogenetics. The following words are used to describe genetic variants of the chromosomes:

• Aneuploidy refers to when there is an incorrect amount of chromosome material: This can be an entire extra set of chromosomes (triploidy), an entire missing chromosome (monosomy), entire extra chromosome (trisomy) or part of a chromosome that is missing/extra (deletion/duplication).
• Trisomy is a genetic condition caused by the presence of an entire extra chromosome in a person’s cells. This can occur with any chromosome, but occurs more commonly with certain chromosomes than others, like Down syndrome (a trisomy of chromosome 21). Some trisomies are only seen in miscarriages and not in live births.
• Mosaic trisomy occurs when an individual has a mixture of cells, some with the typical number of chromosomes (46) and others with an extra copy of a chromosome (47). This happens due to an error in cell division after fertilization, leading to two or more cell populations within the body. The effects of mosaic trisomy depend on the proportion of affected cells and which tissues are involved.
• Copy number variant (CNV) is a change when there are extra or missing copies of a specific DNA segment. CNVs can result from:
  • Deletions - a missing portion of DNA
  • Duplications – an extra portion of DNA (can be one extra copy or multiple extra copies)
  • Each chromosome has two arms: a short arm, called the p arm (shown at the top in the diagram on the right), and a long arm, called the q arm (at the bottom). The size of the copy number variant can vary and may consist of portions of an arm, the entire short (p) or long (q) arm, or the entire chromosome. The size of the copy number variant matters – as the bigger the size of the CNV, the more genetic material is extra or missing.

Variants in Chromosome 9 and Medical Concerns 

Variants in Chromosome 9 are rare, but trisomy 9 mosaicism is one of the more commonly observed trisomies in newborns. This condition, known as Trisomy 9 Mosaic syndrome (T9M), occurs when some cells have an extra copy of Chromosome 9 while others have the typical two copies. In contrast, complete trisomy 9—where all cells have an extra Chromosome 9—often leads to early pregnancy loss (miscarriage).  

T9M is not inherited but occurs due to a random error in cell division, leading to mosaicism. Since trisomy 9 is usually seen in a mosaic form, its severity varies based on how many and which cells have the extra chromosome 9. Common medical concerns include feeding difficulties, slow growth, cleft palate, heart defects, joint and bone issues, kidney or urinary differences, breathing challenges, and developmental delays. Some children may also experience seizures, as well as vision or hearing problems. The severity of symptoms in someone with T9M often depends on the percentage of cells that have the extra Chromosome 9. Determining the exact percentage and distribution of mosaic cells is challenging, as the level of mosaicism can differ between tissue types.  

Because T9M is rare and varies widely between individuals, we believe that collaboration between families, researchers, and medical professionals is essential. Everyone’s experience provides valuable insights that help guide medical care and advance future research.

In addition to T9M, multiple other copy number variants (CNVs) on Chromosome 9 exist. These changes are also associated with a range of physical and developmental differences, including growth abnormalities, birth defects, neurological issues, and delays in development. The specific impact on development and health depends on the type and size of the CNV seen.    

Specialized Care at Lurie Children’s 

Lurie Children’s Trisomy 9 Mosaic syndrome (T9M) and Chromosome 9 Program is the first clinic in the world dedicated to the care of people with T9M and other variants on Chromosome 9. The program aims to evaluate and support patients with T9M and Chromosome 9 copy number variants. If families are interested, there may be opportunities to participate in research in a natural history study on T9M and Chromosome 9 variants. 

The genetic specialists in this clinic, Mindy Li, MD, and genetic counselor Kelsey Hogan, MS, CGC, both have experience with neurodevelopmental disorders, T9M, and other Chromosome 9 variations. Dr. Li is the primary author of a publication on individuals with T9M that includes suggested clinical screening guidelines for this disorder. The team is dedicated to supporting and advocating for both the physical and emotional needs of children and their families.  

As research on T9M continues to evolve, the team at Lurie remains committed to providing expert care and advancing understanding of this rare condition. Through collaboration between families, researchers, and medical professionals, we can drive meaningful progress, improve outcomes, and strengthen support for those affected by T9M & other Chromosome 9 variations. 

Additional Resources  

For more information on T9M, please visit the following sites:  

• Unique – Understanding Rare Chromosome and Gene Disorders: Mosaic Trisomy 9 Information Booklet
• National Organization for Rare Disorders (NORD): Mosaic Trisomy 9 
• SOFT (Support Organization for Families with Trisomy) 

Search our blog Search

---