Rebecca Okashah Littlejohn, MS, CGC
Certified Genetic Counselor
The Children’s Hospital of San Antonio
According to the March of Dimes, about one in 150 babies is born with a chromosome condition.¹ Chromosomes are structures in each of our cells made of tightly coiled DNA. Portions of DNA are called genes. Genes provide the specific instructions that tell our bodies how to grow and develop. Most people have 23 pairs of chromosomes in most of all of their cells for a total 46 chromosomes.
Some individuals have three copies of an entire extra chromosome (i.e. full trisomy) or part of an extra chromosome (i.e. partial trisomy or duplication). The “tri” in trisomy means three and “somy” in trisomy means chromosome. An extra chromosome or part of an extra chromosome can occur in some cells or all cells.
Having a partial or extra chromosome can cause variable health problems. A trisomy can occur with any chromosome, but the three most well-known trisomy conditions are Trisomy 21 (Down syndrome), Trisomy 18 (Edwards Syndrome), and Trisomy 13 (Patau syndrome). We often find that individuals with the same or similar extra copy of chromosome may have similar health or developmental problems. For example, individuals with Trisomy 21 or Down syndrome usually have mild-to-moderate intellectual disability and developmental delay, heart abnormalities, hearing and vision problems, thyroid problems and a number of other problems. Individuals with Trisomy 21 may have some or all of these health problems.
There are also other conditions where individuals have a partial extra chromosome like partial trisomy of chromosome 16p11.2 (i.e. duplication of chromosome 16p11.2). Individuals with this condition often have a low weight, a small head size (microcephaly), and developmental delays, especially in speech and language. Affected individuals also have an increased risk of behavioral problems.6 Individuals with duplication of chromosome 16p11.2 may have some or all of these health problems.
It is important for parents and physicians to know which chromosome or piece of chromosome is extra. Knowing the correct result will help with providing information on occurrence or recurrence, education about inheritance, and information on medical management and research opportunities. Families are also encouraged to find a support group. Support groups whether at the local, state, or national levels can offer resources on challenges that individuals with these conditions may face.
Please join The Children’s Hospital of San Antonio in supporting National Trisomy Awareness Month and celebrating all those individuals with trisomy.
The Genetics Clinic at The Children’s Hospital of San Antonio provides evaluation, diagnosis, genetic counseling, treatment, and management of pediatric and adult patients. Talk to your doctor about a referral to the Genetics Clinic.