March is Trisomy awareness month, so it’s a perfect time to explain “what is trisomy?” Most people have 23 pairs of chromosomes, for a total of 46 chromosomes total. Trisomy is a genetic disorder in which an individual has an extra chromosome (partial or whole). Early identification is important in order to best evaluate, treat, and monitor for any possible developmental deficits or possible medical complications. Educating others of trisomy is important to not only provide a better understanding of the syndromes but to reinforce the notion that early intervention is vital for academic and social success.
Most common Trisomy disorders:
Most common Trisomy disorders:
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.
Klinefelter Syndrome, also called XXY Trisomy, occurs in about 1 in 500-1,000 newborn males. Most variants of Klinefelter Syndrome are much more rare, occurring in 1 in 50,000 or fewer. Affected individuals typically have small testes that do not produce as much testosterone as usual. Testosterone is the hormone that directs male sexual development before birth and during puberty. A shortage of testosterone can lead to delayed or incomplete puberty, breast enlargement (gynecomastia), reduced facial and body hair, and an inability to have biological children (infertility). Some affected individuals also have genital differences including undescended testes (cryptorchidism), the opening of the urethra on the underside of the penis (hypospadias), or an unusually small penis (micropenis). Children with Klinefelter syndrome may have learning disabilities and delayed speech and language development. They tend to be quiet, sensitive, and unassertive, but personality characteristics vary among affected individuals. Learn more about Klinefelter Syndrom at https://rarediseases.info.nih.gov/diseases/8705/klinefelter-syndrome .
Triple X Syndrome occurs in about 1 in 1,000 newborn females. Five to ten girls with Triple X are born in the United States each day. Triple X syndrome is associated with an increased risk of learning disabilities and delayed development of speech and language skills. Delayed development of motor skills (such as sitting and walking), weak muscle tone (hypotonia), and behavioral and emotional difficulties are also possible, but these characteristics vary widely among affected girls and women. Seizures or kidney abnormalities occur in about 10 percent of affected females. Learn more about Triple X Syndrome at https://rarediseases.org/rare-diseases/trisomy-x/.
Trisomy 18, also called Edwards syndrome, occurs in about 1 in 5,000 live births each year in the United States. Individuals with trisomy 18 often have slow growth before birth (intrauterine growth retardation) and a low birth weight. Affected individuals may have heart defects and abnormalities of other organs that develop before birth. Other features of trisomy 18 include a small, abnormally shaped head; a small jaw and mouth; and clenched fists with overlapping fingers. Due to the presence of several life-threatening medical problems, many individuals with trisomy 18 die before birth or within their first month. Five to 10 percent of children with this condition live past their first year, and these children often have severe intellectual disability. 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 severe intellectual disability and physical abnormalities in many parts of the body. Individuals with trisomy 13 often have heart defects, brain or spinal cord abnormalities, very small or poorly developed eyes (microphthalmia), extra fingers or toes, an opening in the lip (a cleft lip) with or without an opening in the roof of the mouth (a cleft palate), and weak muscle tone (hypotonia). Due to the presence of several life-threatening medical problems, many infants with trisomy 13 die within their first days or weeks of life. Only five percent to 10 percent of children with this condition live past their first year.. Learn more about Trisomy 13 on the Genetic Home Reference Trisomy 13 webpage.
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