A simian crease, now more commonly known in medical contexts as a single transverse palmar crease (STPC), is a single line that runs horizontally across the palm of the hand.
While most people have three distinct creases in their palms, this variation occurs when the two upper creases join to form just one.
Only 1.5% of the general population has a simian crease.
The term “simian” refers to monkeys or apes, as they typically possess this crease.
Due to its potential negative or pejorative connotations, medical professionals often prefer the term single palmar crease or single transverse palmar crease.
It is found in approximately 1 out of 30 people (about 3% of the population).
It is twice as common in males as in females.
Simiancreases typically form by the 12th week of gestation in the womb.
In most cases, having a single palmar crease is completely normal and does not indicate any health issues.
It can sometimes be an indicator for certain genetic or developmental conditions:
Down Syndrome: It is present in approximately 45–60% of individuals with Down syndrome.
It has also been associated with Fetal Alcohol Syndrome, Turner syndrome, Klinefelter syndrome, and Trisomy 13.