Genetics |
Causes of Rett SyndromeRett Syndrome is caused by a mutation of the MECP2 gene on the X chromosome, which occurs randomly and can affect all ethnic groups (NORD). Because the mutation is in the X chromosome, it is sex-linked and therefore inherited differently by males and females. It is also dominant. Girls have two X chromosomes, so they will likely only have one chromosome with the defective gene that causes them to have Rett Syndrome. However, boys with the disorder are more strongly affected since they only have one X chromosome and typically do not live to adulthood, unlike girls (MedlinePlus).
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InheritanceRett Syndrome is a sex-linked disorder but is very rarely inherited, with 99% of cases occurring due to a random mutation of the MECP2 gene (Dragich). However rare, it is possible for the mutation to be inherited from a parents' reproductive cell if the mutation arises in either the ovaries or testes - this occurrence is called germline mosaicism. Since the parent's other cells do not have the mutation, they are unaffected but may pass down mutation to his or her child. In even rarer cases, a mother may exhibit only mild or no symptoms of Rett Syndrome and simply be a carrier. This could be possible due to favorable X-inactivation, in which the affected X chromosome is silenced in most cells. In these cases, inheriting Rett Syndrome is possible, although still highly unlikely (NORD).
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Left: A chart demonstrating the inheritance of sex-linked disorders.
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Center: A Punnett Square indicating the inheritance of Rett Syndrome, assuming the mother is a carrier.
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Right: Karyotype representing the mutation in the MECP2 gene that causes Rett Syndrome
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