Fragile X syndrome or FXS is a genetic condition. The approximate prevalence of FXS is one in 3,600 to 4,000 males and one in 4,000 to 6,000 females. FXS can lead to varying degrees of intellectual and behavioral challenges and a range of physical characteristics. Mutations in the FMR1 gene results in deficient production of the protein FMRP, which in turn causes FXS. Individuals can have different forms of the mutated gene. The severity of symptoms depends on how much the mutated gene differs from a healthy FMR1 gene.
Humans have 23 chromosome pairs inherited from both parents. Chromosomes carry genes, so each parent also contributes half of a child's genes. The 23rd chromosome pair contains X and Y sex chromosomes. Females have two X chromosomes (XX), while males have an X and Y (XY). Mothers always contribute an X chromosome to offspring so the father's contribution of an X or Y determines gender. The FMR1 gene is on the X chromosome.
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