Didactyly
Didactyly (from Greek δι- di- "two") or bidactyly is the condition of having two digits on each limb, as in the Hypertragulidae and two-toed sloth, Choloepus didactylus. In humans this name is used for an abnormality in which the middle digits are missing, leaving only the thumb and fifth finger, or big and little toes. Cloven-hoofed mammals (such as deer, sheep and cattle – Artiodactyla) have only two digits, as do ostriches. Monodactyly
Monodactyly (from Greek μόνος monos- "one") is the condition of having a single digit on a limb, as in modern horses and other equidae (though one study suggests that the frog might be composed of remnants of digits II and IV, rendering horses as not truly monodactyl) as well as sthenurine kangaroos. Functional monodactyly, where the weight is supported on only one of multiple toes, can also occur, as in the theropod dinosaur Vespersaurus. The pterosaur Nyctosaurus retained only the wing finger on the forelimb, rendering it also partially monodactyl. As a congenital defect
Among humans, the term "five-fingered hand" is sometimes used to mean the abnormality of having five fingers, none of which is a thumb. Syndactyly
Syndactyly (from Greek συν- syn "together") is a condition where two or more digits are fused together. It occurs normally in some mammals, such as the siamang and most diprotodontid marsupials such as kangaroos. It occurs as an unusual condition in humans. Polydactyly
Polydactyly (from Greek πολυ- poly- "many") is when a limb has more than the usual number of digits.
It is thought that due to the co-occurrence of these two disorders they may have a common etiology.As a feature of GLHS one case study has shown GLHS to co-occur with autism spectrum disorder. Epidemiology
As of 2018 only 36 cases have been reported. History
The first case was reported by Heinrich Obersteiner in 1914. == References ==