About Down Syndrome

According to the Centers for Disease Control and Prevention (CDC), approximately one in every 700 babies in the United States is born with Down syndrome, making Down syndrome the most common chromosomal condition. About 5,000 babies with Down syndrome are born annually in the United States.

Trisomy 21 Nondisjunction Down syndrome is the most common form of Down syndrome, This is caused by an error in cell division called “nondisjunction.” Nondisjunction results in an embryo with three copies of chromosome 21 instead of the usual two. Prior to or at conception, a pair of 21st chromosomes in either the sperm or the egg fails to separate. As the embryo develops, the extra chromosome is replicated in every cell of the body. This type of Down syndrome, which accounts for 95% of cases, is called trisomy 21.

Mosaicism (or mosaic Down syndrome): is diagnosed when there is a mixture of two types of cells, some containing the usual 46 chromosomes and some containing 47. Those cells with 47 chromosomes contain an extra chromosome 21. Mosaicism is the least common form of Down syndrome and accounts for only about 2% of all cases of Down syndrome (Facts about Down syndrome, 2021).

Translocation: In translocation, which accounts for about 3% of cases of Down syndrome, the total number of chromosomes in the cells remains 46; however, an additional full or partial copy of chromosome 21 attaches to another chromosome, usually chromosome 14. The presence of the extra full or partial chromosome 21 causes the characteristics of Down syndrome.

Down syndrome occurs in people of all races and economic levels, though older women have an increased chance of having a child with Down syndrome. A 35-year-old woman has about a one in 350 chance of conceiving a child with Down syndrome, and this chance increases gradually to 1 in 100 by age 40. At age 45 the incidence becomes approximately 1 in 30. The age of the mother, or birthing parent, does not seem to be linked to the risk of translocation.

All three types of Down syndrome are genetic conditions (relating to the genes), but only 1% of all cases of Down syndrome have a hereditary component (passed from parent to child through the genes). Heredity is not a factor in trisomy 21 (nondisjunction) and mosaicism.

Once a parent has given birth to a baby with trisomy 21 (nondisjunction) or translocation, it is estimated that the chances of having another baby with trisomy 21 is 1 in 100 up until age 40. The risk of recurrence of translocation is about 3% if the father is the carrier, and 10-15% if the mother is the carrier. Genetic testing can determine the origin of translocation.

Prenatally

There are two categories of tests for Down syndrome that can be performed before a baby is born: screening tests and diagnostic tests. Prenatal screens estimate the chance of the fetus having Down syndrome. These tests do not tell you for sure whether your fetus has Down syndrome; they only provide a probability. Diagnostic tests, on the other hand, can provide a definitive diagnosis with almost 100% accuracy.

At Birth

Down syndrome is usually identified at birth by the presence of certain physical traits: low muscle tone, a single deep crease across the palm of the hand, a slightly flattened facial profile, and an upward slant to the eyes. Because these features may be present in babies without Down syndrome, a chromosomal analysis called a karyotype is done to confirm the diagnosis.

Individuals with Down syndrome are becoming increasingly integrated into community organizations, such as schools, health care systems, work forces, and social and recreational and therapeutic activities. Individuals with Down syndrome possess varying degrees of cognitive delays, from very mild to severe. Most people with Down syndrome have cognitive delays that are mild to moderate. And due to advances in medical technology, individuals with Down syndrome are living longer, healthier lives than ever before.

Down vs. Down’s syndrome: Down syndrome, rather than Down’s syndrome.

People with Down syndrome should always be referred to as people first.

Instead of “a Down syndrome child,” it should be “a child with Down syndrome.” Also avoid “Down’s child” and describing the condition as “Down’s,” as in, “He has Down’s.”

Down syndrome is a condition or a syndrome, not a disease.

People “have” Down syndrome, they do not “suffer from”

“Typically developing” or “typical” is preferred over “normal.”

“Intellectual disability” or “cognitive disability” has replaced “mental retardation” as the appropriate term.