A simian crease is a single line (crease) that runs across the palm of the hand. People normally have three creases in their palms.

Prominent creases (called flexion creases) appear on the palms of the hands and soles of the feet. The palm normally has three flexion creases. Sometimes, the two horizontal creases fuse to form a single crease. This is called a single palmar crease, or simian crease.

Many structures develop in the fetus in the first few months of gestation. Palmar creases develop early, by the 12th week of life. Some abnormalities in palmar creases indicate problems with development and are associated with disorders like Down syndrome. However, a simian crease appears in approximately 1 out of 30 people. Males are twice as likely as females to have this condition.

A simian crease is often a normal finding, occurring in about 3% of the population. It may also be associated with:

• Down syndrome
• Aarskog syndrome
• Cohen syndrome
• Fetal alcohol syndrome
• Trisomy 13
• Rubella syndrome
• Turner syndrome
• Klinefelter syndrome
• Pseudohypoparathyroidism
• Gonadal dysgenesis
• Cri du chat syndrome

An infant with a simian crease may have other symptoms and signs that, when taken together, define a specific syndrome or condition. Diagnosis of that condition is based on a family history, medical history, and thorough physical evaluation.

Your doctor may ask questions such as:

• Is there a family history of Down syndrome or other disorder associated with a simian crease?
• Have other family members had a simian crease and no other abnormality?
• What was the pregnancy like?
• Did the mother use alcohol while pregnant?
• What other symptoms or physical abnormalities are present?

Based on the answers to these questions, the medical history, and the results of the physical exam, further testing may be necessary.