While it is known that there are many complex genetic roots to autism, the genetics of RD are comparatively simpler - more than 80 percent of patients diagnosed with RD have a specific mutation in the MeCP2 gene on the X chromosome. This mutation is not inherited, but occurs after conception. They found that two had mutations in the MeCP2 gene. The results of the team's study were presented Friday at the International Congress of Human Genetics in Vienna. This explains why RD almost always affects only females.
Females have two copies of the X chromosome, but only one normally remains functional in each cell.
Which copy remains working is random, the researchers say, so in RD females enough normal X chromosomes remain working to support life, but the presence of the abnormal RD containing X chromosome in the rest of the cells causes the disease. Males, on the other hand, have only one copy of the X chromosome. Therefore, boys with the RD-containing X chromosome have no normal chromosome present and die before or shortly after birth, they said. While the role of the MeCP2 gene is still seen as crucial to the development of RD, and maybe autism, new findings have muddied the scientific waters. However, we're finding this occurs more and more as we get in to the genetic roots of different diseases - what we see clinically isn't always as straightforward once we understand the underlying genetics of a disorder.