In honor of National Trisomy Awareness Month, we spoke to a team of genetic counselors from the CHOC Metabolic Clinic. ‘Tri’ refers to three, and ‘somy’ refers to ‘body’ or in this case chromosome- therefore, individuals with a trisomy have an extra chromosome in some or all of their cells, which affects development. Trisomies can occur on any chromosome, and are named for the chromosome for which the extra copy appears. The most common trisomies are Trisomy 21 (Down syndrome), Trisomy 18 (Edwards syndrome) and Trisomy 13 (Patau syndrome).
Healthy babies have 23 pairs of chromosomes, tiny rod-shaped structures in the nucleus of almost every body cell. Each parent contributes half of their child’s 46 total chromosomes. Sometimes random genetic events occur during the formation of eggs and sperm in healthy parents and lead to a child getting an extra copy of a certain chromosome, for a total of 47 chromosomes.
A trisomy is not usually passed down from generation to generation, but rather is the result of two chromosomes sticking together at the time of cell division. This is called non-disjunction, and leads to the baby having an extra chromosome for a specific chromosome pair. Chromosome trisomies can be detected during pre-natal diagnostic testing, but may be detected in the baby’s blood after birth as well, says Kate Partynski, a board-certified genetic counselor in CHOC’s Metabolic Clinic.
CHOC’s genetic counselors, geneticists and other specialists are equipped to help these patients and their families, by providing information, resources and support.
Trisomy 21- Down syndrome
The most common trisomy is Down syndrome, which occurs in one in 733 births. Children with Down syndrome require multidisciplinary care teams to address their unique health care needs and developmental challenges that may include heart defects, intestinal malformations, visual impairment, hearing loss or other conditions.
Because Down syndrome is associated with mild to moderate intellectual ability, early intervention is essential to maximizing the potential of each child, says Karen Leydiker, a board-certified genetic counselor in CHOC’s Metabolic Clinic.
CHOC’s Down syndrome program bridges community services and clinical specialists to ensure the unique needs of each patient are met. The program works in tandem with the Down Syndrome Association of Orange County to provide parents and families access to a comprehensive range of resources, including parent mentors, information for expectant parents and sibling support groups.
Trisomy 18- Edwards syndrome
Trisomy 18, also known as Edwards syndrome, is the second most common human trisomy and occurs in 1 out of every 6,000 pregnancies. This is caused by having three copies of chromosome 18 instead of two. Half of these affected pregnancies will survive to term, and approximately 10 percent of children born with this condition may survive until 1 year of age, with the majority passing away within the first few weeks of life. The high mortality rate is due to complications from brain abnormalities, congenital heart defects, kidney defects and other congenital anomalies, according to Leydiker. For those babies who do survive their first year, it does become a possibility that they can live for several years, but will be expected to be severely developmentally delayed and require multiple organ system support.
Trisomy 13- Patau syndrome
The third most common human trisomy, Patau syndrome, occurs once in every 10,000 births and is caused by having three copies of chromosome 13 instead of two. Babies with this condition have severe structural brain abnormalities, cleft lip, cleft palate, eye abnormalities, heart defect, and due to the severity of the condition rarely live beyond the first few weeks of life. A small percentage of children with this trisomy will survive their first year but are all severely developmentally delayed and require multiple organ system support.
Support Organization for Trisomy provides resources for expectant parents, sibling support, and grief resources for families of children with Trisomy 18 or Trisomy 21.
Genetic counseling resources
CHOC genetic counselors are available to meet with families expecting a child with a genetic condition. “Parents may need time to grieve the loss of the child they thought they would have, and prepare themselves for a different parenting journey than they originally expected,” says Leydiker.
Genetic counseling appointments are not limited only to parents, but are open to family and friends who may have questions about their soon-to-be family member’s condition, or want to learn more.
“A genetic counselor’s role is to provide information and support to parents during what can be a confusing and challenging time,” explains Leydiker. “We try to meet parents where they are emotionally, and provide support and resources in a safe, non-judgmental environment.
“As part of our counseling sessions, we often share a poem with parents called ‘Welcome to Holland’ that tells the story of someone who expected their vacation to take them to Italy, a place they had long dreamed of going. But the plane drops them off in Holland, which is just as beautiful, but very different than what they expected.”
To make an appointment with a genetic counselor, visit the National Society of Genetic Counselors website and select the “Find a Genetic Counselor” tool to find genetic counselors and genetics clinics in your area.
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