Which is MC genetic cause of Mental Retardation

Most common cause of MR is fragile X syndrome. Fragile X syndrome (FXS) is a genetic disorder. FXS is caused by changes in a gene that scientists called the fragile X mental retardation 1 (FMR1) gene when it was first discovered. The FMR1 gene usually makes a protein called fragile X mental retardation protein (FMRP). FMRP is needed for normal brain development. People who have FXS do not make this protein. People who have other <a href=" X-associated disorders</a> have changes in their FMR1 gene but usually make some of the protein. Reference: GHAI Essential pediatrics, 8th edition