Trisomy Awareness Month

During Trisomy Awareness Month in March, the NICHD joins other agencies and organizations in raising awareness about trisomy conditions and the challenges they may pose to individuals and families.

Most people have 23 pairs of chromosomes in most or all of their cells for a total of 46 chromosomes in all. These chromosomes include DNA and other material that provide a blueprint for “building” a person.

Some people have trisomy conditions—those related to having an extra chromosome in most or all of their cells, for a total of 47 chromosomes in all.

An extra chromosome can cause a variety of health problems ranging from mild intellectual and developmental disability (IDD), to severe physical problems.  

The specific health issues of a trisomy condition and how severe those issues are depend on:

  • Which chromosome: An extra copy of some chromosomes is lethal; for example, an embryo with three copies of chromosome 1 will not develop.
  • Whether there is a partial or complete extra chromosome: If cells include only a partial extra chromosome, symptoms are usually milder than if cells have a complete extra chromosome.
  • How many cells have the extra chromosome or partial chromosome: If the extra chromosome is in only a few cells, the symptoms are usually milder than if the extra chromosome is in all or most of cells.
Health conditions and problems associated with trisomy include physical abnormalities, such as extra fingers or toes; physiological issues, such as irregular heartbeat patterns; and problems related to intellectual and developmental functioning.

Most of the time, trisomy conditions are not passed from one generation to the next, but result from a random error that occurs during cell division very early on in development.

Trisomy can occur with any chromosome, but the most well-known syndromes are:

  • Trisomy 21, more commonly known as Down syndrome, occurs in 1 in 691 live births in the United States each year, according to the Centers for Disease Control and Prevention. People with Down syndrome usually have mild-to-moderate intellectual and developmental disability (IDD), heart abnormalities, and are at risk for hearing and vision loss and a number of other health conditions. Learn more about Down syndrome on the NICHD Down Syndrome: Condition Information webpage.
  • Trisomy 18, also called Edwards syndrome, occurs in about 1 in 5,000 live births each year in the United States. Infants with Trisomy 18 often have severe IDD, as well as serious heart problems and other life-threatening issues. Learn more about Trisomy 18 at Genetics Home Reference Trisomy 18 webpage.
  • Trisomy 13, also called Patau syndrome, occurs in about 1 in 10,000 to 16,000 live births each year worldwide. Trisomy 13 is associated with more severe IDD and multiple physical problems, including serious heart problems. Learn more about Trisomy 13 on the Genetic Home Reference Trisomy 13 webpage.

Support Organization for Trisomy 18, 13 and Related Disorders, or SOFT, is a non-profit, volunteer organization that has helped families having children with trisomies for over three decades and is recognized as a primary source of information about trisomy 18, 13 and related disorders. SOFT is a network of families and professionals dedicated to providing support and understanding to families involved in the issues and decisions surrounding the diagnosis and care in Trisomy 18, 13 and other related chromosomal disorders.  Support can be provided during prenatal diagnosis, the child’s life and after the child’s passing.  SOFT is committed to respect a family’s personal decision and to the notion of parent-professional relationships.


Krista Flack, MS OTR/L
Pediatric Occupational Therapist

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