Your hand’s palm has three large creases; the distal traverse palmar crease, the proximal transverse palmar crease, and the thenar transverse crease.

  • “Distal” means “away from the body.” The distal transverse palmar crease runs along the top of your palm. It begins close to your little finger and ends at the base of your middle or index finger, or between them.
  • “Proximal” means “toward the body.” The proximal transverse palmar crease is below the distal crease and somewhat parallel to it, running from one end of your hand to the other.
  • “Thenar” means “ball of the thumb.” The thenar transverse crease runs vertically around the base of your thumb.

If you have a single transverse palmar crease (STPC), the distal and proximal creases combine to form one transverse palmar crease. The thenar transverse crease remains the same.

An STPC used to be called a “simian crease,” but that term is no longer considered appropriate.

STPC can be useful in detecting disorders such as Down syndrome or other developmental problems. However, the presence of a STPC doesn’t necessarily mean that you have a medical condition.

An STPC develops during the first 12 weeks of the development of a fetus, or the first trimester. STPC has no known cause. The condition is common and doesn’t present any health problems for most people.

STPC or other similar palm crease patterns can help your healthcare provider identify a few disorders, including:

Down syndrome

This disorder occurs when you have an extra copy of chromosome 21. It causes intellectual disabilities, a characteristic facial appearance, and an increased chance for heart defects and digestive issues.

According to the Centers for Disease Control and Prevention (CDC), Down syndrome is the most commonly diagnosed genetic condition in the United States.

Fetal alcohol syndrome

Fetal alcohol syndrome appears in children whose mothers drank alcohol during pregnancy. It may cause developmental delays and stunted growth.

Children with this disorder may also have:

Aarskog syndrome

Aarskog syndrome is an inherited genetic condition linked to your X chromosome. The syndrome affects your:

  • facial features
  • skeleton
  • muscle development

An STPC doesn’t typically cause any complications. In one reported case, STPC was associated with fused carpal bones in the hand.

Fused carpal bones can be related to many syndromes and can lead to:

  • hand pain
  • a greater likelihood of hand fractures
  • arthritis

STPC by itself doesn’t cause any health problems and is common among healthy people without any disorders. If you have STPC, your healthcare provider can use it to look for other physical characteristics of various conditions.

If needed, they can order more tests to help them make a diagnosis.