When the egg and sperm unite, all resulting cells carry three copies of chromosome 21. This type, known as complete trisomy 21, accounts for nearly all cases of Down syndrome. Mosaic Trisomy 21 ...

While Emma has Down syndrome — specifically a rare type called Mosaic ... Trisomy 21, which occurs, according to the Cleveland Clinic, “When a developing fetus has three copies of chromosome ...

A century after Down syndrome was first described, scientists discovered that the root cause of this disorder is a condition called trisomy 21 ... chromosome, usually chromosome 14 or 15.

Some have the usual 46 chromosomes and some have 47, which are the ones with the extra chromosome 21 that defines trisomy 21. Although this can cause babies born with mosaic Down syndrome to have ...

14 From this information ... by Clarke et al. 21 in a child with some mongoloid features, who was of normal intelligence. Chromosome analysis revealed her to be a mosaic with a mixture of cells ...

Down syndrome occurs in three forms: - Trisomy 21 (95%): All the body's cells have an extra complete copy of chromosome 21 due to faulty cell division. - Mosaic Down Syndrome (1-2% of the ...