Researchers at the University of Tokyo have discovered that one segment of DNA is responsible for four rare diseases.
As reported in Science Daily, the university team also believes that this segment of DNA may be responsible for diseases, beyond the ones that were evident in the genetic testing.
About the Discovery
This is an important discovery because the team found that the same mutation in dissimilar areas of the genome (an organism’s complete set of DNA) was causing other diseases. Therefore, at some point in the future, one drug targeting the same mutation may be able to treat many different diseases.
Until now, choosing a treatment for certain genetic diseases has been difficult because different mutations were known to cause the exact same disease. One case in point would be the dilemma facing Parkinsons’ treatment. Mutations in five distinctly different genes can cause Parkinson’s disease. Another example is cystic fibrosis– researchers believe that there are about one thousand dissimilar mutations in one gene.
The Old and the New
Prior to the advent of new DNA sequencing techniques, in order to locate a mutation, the researchers had to have an idea of its location. That required searching through forty-six chromosomes in the human genome. Sequencing DNA informs the scientists of the type of genetic information found in DNA.
The new method of sequencing is reliant upon next-generation sequencing (NGS) and advanced data analysis. This all came about because of the researchers’ theories– plus many years of working towards improved sequencing. The university’s research paper was published in Nature Genetics.
Families who have lived with neurodegenerative diseases were finally given answers regarding the cause of their disease.
About Neurodegenerative Disease
The research team turned their attention to neurodegenerative diseases. The term neurodegenerative disease covers many conditions that have an effect on the neurons located in the brain. These diseases include multiple sclerosis, Parkinson’s disease, Huntington’s disease, dementia, and Alzheimer’s.
Symptoms of these diseases include uncontrolled movement, imbalance, cognitive impairment, difficulty swallowing and weakness of the arms or legs. The typical onset of these diseases occurs in adulthood.
Fragile X Syndrome is a rare neurodegenerative disease that is seen in one out of ten thousand births. It was identified almost twenty years ago by the genetic code “CGG”, which was repeated on the X chromosome anywhere from twelve to hundreds of times.
The research team theorized that the genetic mutations causing the diseases must be similar, despite the fact that the mutations were found in different genes.
A computer program was developed that searched for CGG sequences throughout the healthy human genome. It could identify short segments that contain CGG repeat mutations within specific genetic areas. With this new program, the team could determine which locations to sequence in DNA in order to identify the gene.
This narrowed the search to genome locations that showed patients having a large proportion of CGG repeats where healthy people didn’t show any. Most importantly, it showed where the CGG repeat mutations existed in the patient’s genes, which meant researchers were able to perform more effective sequencing.
About the Discovery
The team discovered that CGG noncoding expanded “tandem repeats”, although located in different regions in the genome, caused all four of the disorders that they had been observing.
Tandem repeats are generally known to be associated with various neurodegenerative diseases. Yet they also appear in abundance in the genome’s functional regions. This is an indication that repeats in coding sequences could be beneficial as well.
Tandem repeats can also result from other genetic code letters that undergo unusual repetition in any area of the genome.
Where are We Going From Here?
The long-term goal of the researchers is to gain insight into the common diseases that are caused by various types of noncoding tandem repeat mutations. They have amyotrophic lateral sclerosis (ALS) treatment in their sights.