Palmar creases develop early, by the 12th week of life.

They often arise in the skin folds, especially the palmar creases.

This is called a single palmar crease, or simian crease.

Some abnormalities in palmar creases indicate problems with development and are associated with disorders like Down syndrome.

Increased incidence of single transverse palmar creases.

Palmar crease xanthomas may also occur.

Hyperlinear palmar creases, which are many and exaggerated skin creases (lines) in the palms of the hand.

Other features include a single (simian) palmar crease, long, slender fingers, flat feet and cryptorchidism (in males).

Other features may include a small lower jaw (micrognathia), cubitus valgus, soft upturned nails, palmar crease, and drooping eyelids.

Xanthoma striatum palmare is a cutaneous condition characterized by xanthomas of the palmar creases which are almost diagnostic for dysbetalipoproteinemia.

Skeletal - Joint anomalies including abnormal position and function, altered palmar crease patterns, small distal phalanges, and small fifth fingernails.

The syndrome may also include various dermatoglyphics, including transverse flexion creases, distal axial triradius, increased whorls and arches on digits, and a single palmar crease.

A unilateral single palmar crease was also reported in a case of chromosome 9 mutation causing multiple basal cell nevus syndrome and Robinow/brachydactyly 1 syndrome .

Increased tanning may be noted, particularly in sun-exposed areas, as well as darkening of the palmar creases, sites of friction, recent scars, the vermilion border of the lips, and genital skin.

Minor physical anomalies (MPAs) are relatively minor (typically painless and, in themselves, harmless) congenital physical abnormalities consisting of features such as low-seated ears, single transverse palmar crease, telecanthus, micrognathism and furrowed tongue.

Other differences often include a single transverse palmar crease ("Simian line") (in 50%), and patterns in the hypothenar and interdigital areas, lower ridge counts along digital midlines, especially in little fingers, which corresponds to finger shortening in those with Down's syndrome.

In humans, a single transverse palmar crease is a single crease that extends across the palm of the hand, formed by the fusion of the two palmar creases (the heart line and the head line) that people typically have.

Single palmar creases are less common than two palmar creases, however 10% of the population have one palmar crease on one hand and 5% have one palmar crease on both hands.