deep crease in the palm of the hand
Single transverse palmar crease 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 (known in palmistry as the "heart line" and the "head line") and is found in people with Down syndrome.[1][2][3] However, it is not an indication that a person with single transverse palmar crease has to have Down syndrome. It is also found in 1.5% of the general population in at least one hand.[4]