Literally, “hooking or curving of the joints”. The underlying problem is too much fibrosis – either muscles are relatively shorter or there is excess connective tissue. There’s quite an active discussion about what percentage of arthrogryposis cases are due to what we might call mechanical problems before birth versus genetics. The characteristics are joints are not very flexible and may have unusual ‘default’ positions – feet may be positioned with toes curved toward the center and hands with fingers closer to the elbow (out of the horizontal plane).
There are currently thought to be three classifications: distal, amyoplasia and syndromic. Distal primarily impacts the hands and feet; amyoplasia is more widespread and impacts the legs, arms and neck; syndromic can impact internal muscles such as the diaphragm and heart.
There are 15 types of arthrogryposis – I don’t know which of these are linked to something mechanical and with are thought to be linked to a gene. In terms of immediate problems in a young child like being able to grasp things or walk I do not know if it matters which type one has.
Wikipedia (https://en.wikipedia.org/wiki/Arthrogryposis) claims 35 genes are associated with arthrogryposis. I have found only 26 (see heavily clipped SAITO screenshots below), so I will have to ask what I missed. I am mostly concerned that my search parameters were not broad enough.