aw-welcome to the club! It's called a simian crease (yep, like the monkey!) or more politically correct these days a singular palmar crease. A palm reader told me that it means your emotions and logic are closely entwined and basically trip each other up. For me, that is very true! My son has them on both hands-when he was born they thought he had Down's since that is often the case. He doesn't have Down's and instead is near genius intelligent and very intense. I have my moments but only one hand is creased so I'm not nearly so smart or intense as he is.
It's associated with some birth defects, one heart defect that I seem to remember too but it's been a while since I've read up on it. Fetal alcohol syndrome too but neither my mother nor I drank while pregnant... just a fluke for us I believe unless one of the syndromes catches up to us!
""The Simian Line gives the ability to focus on one thing, absolutely, to the exclusion of all else. These people generally achieve and accomplish far more than most, developing techniques and inventions that will last for generations. They also experience far more misfortune than most, usually due to the same intensity that drives them. A truly double-edged sword.
When the Simian Line occurs, the "Great Quadrangle" is entirely missing. There is no distinction between what is desired (the Heart) and what is thought (the Head). The result is an incredible intensity of nature, but a strong tendency to rush into all things without thinking them through.""
This describes me to a T and probably my son too: ""People with Simian Lines generally live their life differently than most other people who do not have Simian Lines. Not necessarily living better nor worse. Just living more intensely with an undercurrent of uneasiness. ""