What is the Difference Between Trisomy 13 and 18?

Trisomy 13 and 18 are genetic disorders that result from an extra copy of chromosome 13 or 18, respectively, instead of the usual two copies. Both disorders involve a combination of birth defects, including severe learning problems and health issues that affect nearly every organ in the body. However, there are some differences between the two:

• Incidence: Trisomy 13 occurs in 1 out of every 10,000 to 50,000 newborns, while trisomy 18 occurs in 1 out of every 5,000 to 7,000 newborns.
• Survival: Most babies born with trisomy 13 or 18 die by the time they are 1 year old, with over 95% of trisomy 18 children dying within a year and 60% dying within the first two months. However, some babies with these disorders do survive the first year of life, and there are a few reports of babies with trisomy 13 or 18 surviving to their teens, although this is unusual.
• Causes: Both trisomy 13 and 18 are most commonly caused by a maternal meiotic nondisjunction during the formation of egg or sperm cells. In trisomy 13, a minority of cases are caused by an unbalanced Robertsonian translocation, while in trisomy 18, only 5% of cases are due to a paternal meiotic nondisjunction.
• Phenotypic Features: Trisomy 13 is characterized by a disturbed embryogenesis of the prosencephalon, with major phenotypic features including small-for-gestational-age fetuses, central nervous system anomalies, midline facial defects, and urogenital malformations. In contrast, trisomy 18 is typified by a high fetal loss rate of 97% for trisomy 13 conceptions and a shorter survival postnatally.

Both disorders are not preventable, and there is no reason to believe a parent can do anything to cause or prevent trisomy 18 or 13 in their child. The risk of having a baby with trisomy 13 or 18 increases slightly each year as the mother's age increases, especially after the age of 35.

Comparative Table: Trisomy 13 vs 18

Trisomy 13 and 18 are two genetic disorders also known as Patau syndrome and Edward syndrome, respectively. They are caused by the presence of extra copies of chromosomes 13 and 18, respectively, in the cells of an individual. Here is a table comparing the differences between Trisomy 13 and 18:

Despite the genetic differences, both disorders share similarities such as being genetic conditions caused by the presence of extra genetic materials and diagnosed through samples obtained from amniocentesis and chorionic villus. Both syndromes are also associated with severe birth defects and health problems that affect nearly every organ in the body.