Slide 1: Fragile X syndrome is the most common cause of intellectual disabilities that can be inherited. Slide 2: It is caused by a change, or mutation,in a specific gene on the X chromosome. Slide 3: This gene is called the Fragile X intellectual disabilities – one gene, or F-M-R ONE gene for short. Insert new slide: The F-M-R ONE gene is found in every cell of the body… Slide 4: … but the protein it makes is essential for normal brain development. Slide 5: In the case of fragile X syndrome, the F-M-R One gene either does not make this protein, or makes too little of it, and so the brain does not develop normally. Slide 7: To understand the type of mutation that causes fragile X syndrome, we first need to understand some basic genetics. DNA is made up of four chemical building blocks called nucleotides: Adenine, Cytosine, Guanine, Thymine. Slide 8: These four nucleotides are represented by their first letters: A-C-G-T. They are then strung together one after the other to make up a gene, such as the F-M-R ONE gene. Slide 9: The gene acts like a set of instructions that tells the cell how to make a specific protein. Slide 10: At the beginning of the F-M-R ONE gene, there is a section with the letters see-gee-gee that repeat over and over. Slide 11: In most people, the number of see-gee-gee repeats is small – between 6 and 44 repeats. Slide 12: In other people, the see-gee-gee pattern repeats between 45 and 54 times. This is called an intermediate repeat. Slide 13: And still other people can have the see-gee-gee repeat between 55 and 200 times. This is called a premutation, but the protein is still produced and the brain develops normally. Slide 14: Fragile X syndrome occurs when there are more than 200 see-gee-gee repeats, which is also called a full mutation. Slide 15: The large number of see-gee-gee repeats results in the gene turning off… Slide 16: …and no protein is made. Slide 17: This is the cause of 95% of the cases of fragile X syndrome.