Researchers say they've gained new understanding of a genetic anomaly known as the "fragile X syndrome," the most commonly seen cause of inherited intellectual disabilities.
In Fragile X Syndrome a gene is disabled, shutting of an electrical signal meant to regulate proteins, resulting in a range of neurological and behavioral symptoms.
Researchers at Washington University in St. Louis say they've gained insight into the condition through studies of a patient with a mutation, rather than a complete disabling, in a specific gene, leading to exhibition of only some of the disorder's symptoms.
The syndrome is normally the result of the disabling, through a gene defect, of the fragile X mental retardation protein and loss of the regulation of the brain's electrical signals.
However, the study patient displayed only a single error in the fragile X mental retardation (FMR1) gene, and thus exhibited only two of the main symptoms of the disorder, intellectual disability and seizures.
"This individual case has allowed us to separate two independent functions of the fragile X protein in the brain," says study co-author Vitaly A. Klyachko, a professor of physiology and cell biology. "By finding the mutation, even in just one patient, and linking it to a partial set of traits, we have identified a distinct function that this gene is responsible for and that is likely impaired in all people with fragile X."
Fragile X syndrome is estimated to occur in about one in 5,000 males, and strikes males particularly because the FMR1 gene is on the X sex chromosome.
In addition to the intellectual disability and seizures seen in the study patient, people with the syndrome can be subject to anxiety and symptoms of autism spectrum disorders.
There are often also physical symptoms including flat feet or enlarged heads, the researchers note.
In the patient identified in the study, the single mutation in the DNA code of the FRM1 gene meant the individual had intellectual disability and seizures but did not display any of the physical features associated with the syndrome, nor did the individual show any symptoms of autism.
"This patient presents a case of partial fragile X syndrome associated with mutated, rather than absent, FMRP," says Klyachko. "As far as I know, this is the only known case of this.
"It's a unique opportunity to parse out the functions of FMRP. What does this mutation impair to cause only two symptoms of fragile X?"
There may be additional problems caused by both the mutation and by fragile X syndrome, the researchers acknowledge, but the current study has at least identified one source of dysfunction that was previously unknown.
