What are the genetic changes related to multiple pterygium syndrome ?
Mutations in the CHRNG gene cause most cases of multiple pterygium syndrome, Escobar type and a smaller percentage of cases of lethal multiple pterygium syndrome. The CHRNG gene provides instructions for making the gamma () protein component (subunit) of the acetylcholine receptor (AChR) protein. The AChR protein is found in the membrane of skeletal muscle cells and is critical for signaling between nerve and muscle cells. Signaling between these cells is necessary for movement. The AChR protein consists of five subunits. The  subunit is found only in the fetal AChR protein. At about the thirty-third week of pregnancy, the  subunit is replaced by another subunit to form adult AChR protein. The replacement of fetal AChR by adult AChR is the reason most people with multiple pterygium syndrome, Escobar type do not have problems with muscle movement after birth.  CHRNG gene mutations result in an impaired or missing  subunit. The severity of the CHRNG gene mutation influences the severity of the condition. Typically, mutations that prevent the production of any  subunit will result in the lethal type, while mutations that allow the production of some  subunit will lead to the Escobar type. Without a functional  subunit, the fetal AChR protein cannot be assembled or properly placed in the muscle cell membrane. As a result, the fetal AChR protein cannot function and the communication between nerve cells and muscle cells in the developing fetus is impaired. A lack of signaling between nerve and muscle cells leads to akinesia and pterygium before birth, and may result in many of the other signs and symptoms of multiple pterygium syndrome.  Mutations in other genes, most providing instructions for other AChR protein subunits, have been found to cause multiple pterygium syndrome. Changes in these genes can cause both the lethal and Escobar types of this condition, although they account for only a small number of cases. Some people with multiple pterygium syndrome do not have an identified mutation in any of the known genes associated with this condition. The cause of the disease in these individuals is unknown.