This diagram represents a map the X Chromosome.
The specific colors don’t represent anything except to indicate different regions on the map and the fuzzy colors below represent the influence of these genes on body systems. These regions have been created by scientists to help keep track of where specific genes are found. There are two arms (or major sections) the short arm is called Xp and the long arm is called Xq. Regions of each of these arms are designated by numbers in order of how far the region is from the area where the two arms meet. At the far end of the log arm is a section designated as Xq28. The MECP2 gene and many other genes are located in this region.
Xq28 duplication is said to occur when all or part of the Xq region is duplicated. MECP2 duplication is said to occur when the MECP2 gene is duplicated. Some families have been given a diagnosis of Xq28 Duplication Syndrome and some have been given a diagnosis of MECP2 Duplication Syndrome. Although technically these could mean slightly different things, in most cases these diagnoses refer to the same thing. A section of the Xq28 region is duplicated including the MECP2 gene and this results in a wide variety of symptoms. The diagram below compares a normal X chromosome with one that has an Xq28 duplication. This illustrates the most frequent kind of duplication.
In the case of Xq28 triplication, there is third copy of Xq28 and this usually results in more severe symptoms. Not all MECP2 duplications produce MECP2 Duplication syndrome. A syndrome can only be said to occur if the duplication produces symptoms. Males have only one X chromosome, but females have two. When females have one normal X and one X with the Xq duplication, they do not typically have symptoms and are considered to be carriers. These individuals escape most of the effects of the duplication because, while females have two Xs in each cell, they only use one. Which one they use in each cell is normally seen to be random, but when the duplication occurs, they appear to be able to selectively turn off the chromosome with the duplication and use the one without it. This process is called skewing.
In some cases the duplication is not a result of extra Xq28 material attached to the X chromosome. In these cases some Xq28 genes have migrated to another chromosome, for example chromosome 21 or chromosome 22. This kind of duplication affects males and females in much the same way, because females cannot compensate for this by inactivating the source of the extra Xq28.