Doctors have known for many years that patients with fragile X syndrome, the most common form of inherited intellectual disability, are often also diagnosed with autism. But little has been known about how the two diagnoses are related.
Now a collaborative research effort at Duke University Medical Center and Rockefeller University has pinpointed the precise genetic footprint that links the two. The findings, published online in the journal Nature on Dec. 12, 2012, point the way toward new genetic testing that could more precisely diagnose and categorize the spectrum of autism-related disorders.
Fragile X syndrome is the most well understood single-gene cause of autism. It results from defects on a small part of the genetic code for a protein that researchers have dubbed the fragile X mental retardation protein, or FMRP.
Normally, FMRP plays an important role controlling production of other proteins in the brain and other organs. It does this by looking for specific genetic patterns located on the messages encoding proteins. When it locates these genetic flags, it attaches to them and, along with other signals, controls where and when protein is made.
In fragile X syndrome, this process breaks down because a defect in the gene causes the body to produce too little, or in some cases, none of the FMRP protein. As a result, additional proteins it would normally regulate are made in the wrong place and at the wrong time. Until now, little was known about how this process worked in people with the autism.
Using a combination of laboratory experiments and advanced bioinformatics, the research team, led by Thomas Tuschl, PhD, a Howard Hughes Medical Institute investigator at Rockefeller University, and Uwe Ohler, PhD, an associate professor in Biostatistics and Bioinformatics at the Duke Institute for Genome Sciences & Policy, identified both the genetic flags that FMRP is looking for and the genes it targets.
The researchers discovered that FMRP directly controls at least 93 genes that have been independently linked to autism, as well as Angelman, Prader-Willi, Rett and other neurologic syndromes that have overlapping features with autism.
Additional research using a mouse model of fragile X syndrome revealed that the animals had abnormal protein production not only in the brain, but also in the ovary. The findings confirmed that the absence of FMRP protein causes ovarian insufficiency, which is common among women affected by fragile x syndrome.
"We now know not only which genes are linked to FMRP, but we can locate exactly where they interact," said Ohler. "Down the road, this finding could lead to more detailed genetic tests that take into account the subtle ways that genes get turned on and off."
Physicians who work with fragile X patients know that each patient's abilities and challenges are unique. Some individuals have almost no disability, while others have more severe physical and intellectual disabilities. Approximately 2 percent to 6 percent of children with autism are also diagnosed with fragile X and about one-third of fragile X patients also meet the criteria for autism.
The new discovery should now enable researchers to examine the common molecular pathways leading to all forms of autism. Identification of those pathways could also lead to more targeted treatments for both fragile x and autism.
"We can now look for changes in the FMRP binding sites of genes to identify potential new genetic links to autism-spectrum disorders," said Neelanjan Mukherjee, a Duke post-doctoral scientist who contributed to the research.
Duke University Medical Center: http://www.dukemednews.org
This press release was posted to serve as a topic for discussion. Please comment below. We try our best to only post press releases that are associated with peer reviewed scientific literature. Critical discussions of the research are appreciated. If you need help finding a link to the original article, please contact us on twitter or via e-mail.
When you’re the size of a human, you worry about lions and tigers and bears. But if you’re …
An amateur fossil hunter has unearthed a 7ft skeleton of a carnivorous marine reptile on a beach in south Wales.
European regulators have recommended approval of the first medicine containing stem cells to treat a rare condition caused by burns to the eye.
Ecologists say birds could hear the oncoming storm from over 100 miles away
Marine scientists plumbing the deepest part of the ocean sent microphones and collection probes baited with chicken to the bottom of a trench near Guam. Now they watch, wait ... and listen.
Lead author of two retracted papers resigns her position after failing to reproduce new approach to generating stem cells
The winners of the 2014 Olympus BioScapes Digital Imaging Competition capture a rat brain, the mouthparts of a vampire moth and other small wonders
By analysing brain activity linked to hand and arm movements, a team has created a robotic arm that a paralysed woman can control with her thoughts
Adding laser tips to ordinary shoes can improve the stride and pace of people with Parkinson's disease
Technique could someday help repair injuries