Causes+of+Down+Syndrome

Citation: Salem Health

Causes
Down Syndrome is one of the most common chromosomal defects. Down syndrome begins at the duplication of chromosomes. A patient with Down syndrome has an extra 21st chromosome, which leaves them with 47 total chromosomes instead of the regular 46. Though it isn't an entire chromosome 21, it could be just parts of it. 75% of down syndrome cases are in the egg. ===Non Disjunction: A malfunction of mitosis, resulting in cells with an abnormal chromosome number. === This occurs through a process known as non-disjunction. When the chromosome replicates, it does not do so properly. When chromosome 21 is supposed to separate to be duplicated, it stays stuck together. This results in the duplication creating an extra chromosome.

Incidences of Down Syndrome
Down syndrome is a disorder where the incidences of the disorder grow as the maternal age grows. As the mother ages, her egg cells also obviously age with her. As the egg cells grow older, the chances that your child will develop with Down syndrome increase. For a couple aged 38, the number of children born with down syndrome is approximately 1/177. In just one year, for a mother aged 39, it grows to 1/139. By the time you reach age 45, the rate has grown to an astounding 1/32.

The above image is a karyotype, or diagram of all of the chromosomes that someone has, for a person with down syndrome. You can see that while most of the chromosomes are in pairs, chromosome 21 has three parts instead of two.