THE DOWN SYNDROME

Down syndrome is a chromosomal condition characterized by the presence of an extra copy of genetic material on the 21st chromosome, either in whole (trisomy 21) or part (such as due to translocations). The effects and extent of the extra copy vary greatly among people, depending on genetic history, and pure chance.

 Down syndrome occurs in all human populations, and analogous effects have been found in other species such as chimpanzees.

TYPES OF DOWN SYNDROME

Trisomy 21

When the ova and sperm, they do originate from cells in which, when divided, its 46 separate chromosomes: 23 are to a cell and their partners are going to another, that each has 23 chromosomes . But sometimes it happens that this division and separation of the pairs of chromosomes are not performed correctly, ie, one pair of chromosomes (in our case the pair 21) but does not separate the two chromosomes 21 are held together and in a cell (egg or sperm) divided.

                         

                          

 

                      TRANSLOCATION

 It is because the parent have in the cells of your body, rather than two complete chromosome 21 is normal, a complete chromosome 21 plus a piece of another chromosome 21 broke off and was attached to another chromosome (suppose that one of the pair 14).

                           

Mosaicism

Appears in 1.5% of children with Down syndrome.Situation in which cells and sperm from 23 normal chromosomes , and therefore the first cell that is formed from the merger of two is normal and has its 46 chromosomes. But over the first division of that cell and its daughter comes in one of them the same phenomenon of non-disjunction or non-separation of the pair of chromosome 21 that we mentioned earlier, so that a cell will have 47 chromosomes , three of which will be of par 21.

CHARACTERISTICS

• Poor muscle tone.
• Angular-shaped eyes.
• Small stature.
• Feet wide and short fingers.
• Small nose.
• Small head.
• Obesity trend
• Slow physical and intellectual development

 DIAGNOSTIC

To detect chromosomal abnormalities during the prenatal period are used unambiguously chromosome counting techniques, making it necessary to have a fetal cell. Access to embryonic cell material may pose a risk to both mother and fetus, so its indication is limited to pregnancies in which it has identified a risk of trisomy than the general population (triple positive test, maternal age 35 or over 50 parental, personal or family history of SD, or parents carrying a balanced translocation or other chromosome abnormalities).

The technique most often used to obtain fetal genetic material is the Amniocentesis.