Did you know?

Did you know that there are three types of Down Syndrome?

TYPES OF DOWN SYNDROME

There are 3 chromosomal patterns that result

in Down syndrome.

1. Trisomy 21 (nondisjunction) is caused by a faulty

cell division that results in the baby having three

#21

chromosomes instead of two. Prior to or at conception,

a pair of #21 chromosomes in either the egg

or the sperm fails to separate properly. The extra

chromosome is replicated in every cell of the body.

Ninety five

percent of all people with Down syndrome have

Trisomy 21.

2. Translocation accounts for only 3% to 4% of all

cases. In translocation a part of chromosome #21

breaks off during cell division and attaches to

another chromosome. The presence of an extra

piece of the 21st chromosome causes the characteristics

of Down syndrome. Unlike Trisomy 21,

which is the result of random error in the early cell

division, translocation may indicate that one of the

parents is carrying chromosomal material that is

arranged in an unusual manner.

Genetic counseling can be sought to ascertain

more information when these circumstances occur.

3. Mosaicism occurs when nondisjunction of chromosome

#21 takes place in one of the initial cell divisions

after fertilization. When this happens, there

is a mixture of two types of cells, some containing

46 chromosomes and some with 47. The cells with

47 chromosomes contain an extra 21st chromosome.

Because of the “mosaic” pattern of the cells,

the term mosaicism is used. This type of Down syndrome

occurs in only one to two percent of all

cases of Down syndrome.

Regardless of the type of Down syndrome a person

may have, a critical portion of the 21st chromosome is

present in all or some of their cells. This additional

genetic material alters the course of development and

causes the characteristics associated with the syndrome.

information from the NADS.org web site

Be gentle.