Clinical_Dialogues （上海交大仁济临床医学院《医学专业英语》课件PPT）.ppt

Genetics  Yu Lu Department of Rheumatology Ren Ji Hospital Achondroplasia Achondroplasia vs. Chondroplasia (软骨发育不全)　（软骨生成） a- chondro- Plasia What is achondroplasia? Achondroplasia is a genetic disorder of bone growth that is evident at birth. It affects about one in every 25,000 births and it occurs in all races and in both sexes. Its depiction in ancient Egyptian art makes it one of the oldest recorded birth defects. The word achondroplasia is derived from Greek and means without cartilage formation, although individuals with achondroplasia do have cartilage. During fetal development and childhood, cartilage normally develops into bone, except in a few places, such as the nose and ears. In individuals with achondroplasia, something goes wrong during this process, especially in the long bones (such as those of the upper arms and thighs). The rate at which cartilage cells in the growth plates of the long bones turn into bone is slow, leading to short bones and reduced height. What does?a person with achondroplasia look like? A child with achondroplasia has a relatively normal torso and short arms and legs. The upper arms and thighs are more shortened than the forearms and lower legs. Generally, the head is large, the forehead is prominent and the nose is flat at the bridge. Sometimes, the large head size reflects hydrocephalus (excess fluid in the brain), and require surgery.  Hands are short with stubby fingers. There is a separation between the middle and ring fingers (trident hand). Most individuals with achondroplasia eventually reach an adult height of about 4 feet. What causes achondroplasia?(1) Achondroplasia is caused by an abnormal gene located on one of the chromosome 4 pair (humans have 23 pairs of chromosomes). In some cases, a child inherits achondroplasia from a parent who also has the condition. If one parent has the condition and the other does not, there is a 50 percent chance that their child will be affected. If both p