1 Autism Disorder (Rett) Reversible?
Mouse Study Shows Rett Syndrome -- a Devastating Autism Spectrum Disorder -- May Be Curable
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Rett Syndrome: A Devastating Autism Spectrum Disorder continued...
Boys have only one X chromosome. If they inherit a mutant MECP2 gene, they usually die as infants.
But girls have two X chromosomes. If they inherit the mutant gene from one parent, they almost always get a good copy of the gene from the other parent. X-gene expression is random in females, so girls with a single copy of the gene still have some MECP2 gene function.
That rescues girls from death. "But the price of the rescue is Rett syndrome," Bird says.
Today, Chelsea is confined to a wheelchair. She must be tube-fed. She cannot use her hands or make any purposeful movements, and she suffers daily seizures.
But Coenraads says Chelsea also "is a social, affectionate, loving child who has incredible patience and wisdom beyond her years."
Now Coenraads can hope that she'll one day see Chelsea recover from the illness that imprisons her.
Coenraads' hope is professional as well as personal. She's co-founder and director of research at the Rett Syndrome Research Foundation, which partially funded Bird's research.
"This raises the possibility that Rett syndrome and related postnatal disorders are reversible," Coenraads says. "It is extremely encouraging. This suggests there is no window of opportunity in which you have to act, so women who have suffered for years may get helped."
Also encouraging is the possibility of reversing other diseases that involve MECP2 mutations.
"We are only now getting a handle on how many conditions involve MECP2 mutations. Schizophrenia, movement disorders, mental retardation with seizures -- Rett syndrome is just scraping the tip of the iceberg," Coenraads says.
Possible Rett Syndrome Treatments
Bird's study used mice genetically engineered to carry a MECP2 gene switched off by a genetic element called a stop cassette. These mice act just like humans with Rett syndrome -- their paws can't grasp and they can't walk. They also become obese, something not seen in human Rett patients.
The MECP2 stop cassette in the mice carries a kind of ejection button triggered by a drug. When mice are given the drug, the stop cassette is ejected and their MECP2 genes start working again.
If this is done slowly enough, the mice begin acting like normal mice.
Humans, of course, aren't genetically engineered to carry ejectable stop cassettes. This means that switching on MECP2 function isn't a simple matter.
Bird says there are three likely approaches to a Rett syndrome treatment.
One is a gene therapy that would give people a functional MECP2 gene. That's going to be especially tricky, as too much of this gene is as bad as too little. But gene therapy research may one day be able to solve the problem.
Another idea would be to take advantage of the fact that most females already carry a good MECP2 gene in every cell of their body. It's just that many of these genes are inactive.