Rare 'mirror hand' syndrome causes people to have a completely symmetrical hand
A rare medical condition can leave people with a mirror hand, with the fingers on either side of the hand matching up.
The rare congenital condition is called ulnar dimelia or mirror hand.
People with a mirror hand would usually have seven or eight digits. They have a digit in the middle and three fingers on each side. They won't have a thumb.
The three fingers on either side of the central finger are middle, ring and smaller fingers.
The exact cause of the rare condition is unknown. It can be diagnosed either at birth or on an ultrasound before the birth.
If someone is born with a mirror hand, it can be treated with surgery. But an operation would only improve the hand's functioning or change its appearance.
In a case reported in the US National Library of Medicine in 2018, a two-month-old girl had extra digits due to a condition called polydactyly. Some of her fingers were amputated.
The little girl underwent several surgeries after which she had an ordinary number of fingers on her hand.
Only 70 cases of ulnar dimelia had been documented at the time the report was published.
The medics wrote, "Ulnar dimelia is a very rare developmental anomaly of the upper limb. There are only approximately 70 cases described in the literature."
They said, "“Ulnar dimelia, called also the mirror-hand, is classified to the 3rd group of congenital hand malformation, according to the classification proposed by Swanson [Swanson 1976] and adopted by the American Society for Surgery of the Hand (ASSH) and the International Federation of Societies for Surgery of the Hand (IFSSH)."
They noted, "In the presented case of type II ulnar dimelia an anatomical correction of the hand was possible. The result of surgical treatment in both functional and cosmetic aspects was, in authors' opinion, good."