Autism spectrum disorder (ASD) is the collective term used for diagnosing a range of autism-related conditions centered on communication deficits, impaired social interaction skills and the presence of certain ritualized or repeated behaviors. One especially severe form of ASD, called Rett’s disorder or Rett syndrome, is a genetic condition that profoundly alters the course of normal brain development. According to the results of a study published in August 2013 in the Journal of Neuroscience, doctors may one day be able to ease the effects of Rett syndrome with gene therapy.
Rett Syndrome Basics
Rett syndrome is an incurable condition that first appears in affected infants roughly 6 months after birth. Initially, its effects manifest as unusually slow development of brain and head size. At some point between the ages of 1 year and 18 months, the impact of the condition grows more severe and results in a significant decline in the ability to control isolated or coordinated body movements. The syndrome also triggers deficits in verbal and nonverbal communication skills and a decline in normal thought processing. In some cases, affected children stop speaking entirely; however, some functional level of nonverbal communication skill typically reemerges at a later point in time.
Additional symptoms of Rett syndrome commonly include a loss of interest in the outside world, an unusually irritable temperament, repetitive hand movements, atypical patterns of eye movement and the presence of atypical behaviors such as unexplained laughing or screaming, the use of odd facial expressions or unexplained clasping of the scalp or articles of clothing. Other physical effects of the syndrome include seizures, scoliosis, unusually rapid or delayed breathing, constipation and potentially fatal heartbeat irregularities.
Girls make up the vast majority of the infants affected by Rett syndrome. Although the condition is genetic, it does not pass through family bloodlines. Instead, the Mayo Clinic explains, it occurs when a developing fetus experiences certain types of random genetic mutation. While boys rarely suffer from Rett syndrome, most affected males develop unusually severe forms of the disorder that result in stillbirths or early infant death. With ongoing support and care, most girls (and a small minority of boys) born with the syndrome live into their 50s.
Gene Therapy Basics
Gene therapy gets its name because it uses genes — the packets of DNA found in every human cell — to treat the symptoms of certain illnesses or stop those illnesses from happening. In some cases, the therapy involves replacement of a damaged gene with a functioning version of the same gene. In others, it involves the introduction of completely new genes into the body. In still other cases, it involves “turning off” a defective gene in order to stop it from producing its unwanted effects. Currently, all forms of gene therapy are considered experimental procedures, the U.S. National Library of Medicine’s Genetics Home Reference reports. For this reason, doctors typically only consider use of the therapy, even in preliminary testing, when they deal with incurable conditions.
Potential Use in Rett Syndrome Treatment
Scientists know which particular gene is responsible for producing the symptoms of Rett syndrome. Essentially, this gene functions as a master switch that triggers negative effects by altering the function of numerous other genes. Unfortunately, because of the nature of the interaction between these multiple genes, conventional medications have no usefulness in easing the syndrome’s effects. In the study published in the Journal of Neuroscience, a multi-institution research team used laboratory experiments on mice to examine the potential use of gene therapy as a Rett syndrome treatment. They did this by injecting healthy copies of the master gene into a specific species of virus, then introducing copies of that virus into the bodies of Rett syndrome-affected mice.
After reviewing the results of their experiments, the study’s authors found that gene therapy substantially increased the number of healthy copies of the Rett syndrome master gene in the bodies of the mice. In turn, this increase in healthy gene copies led to a significant reduction in symptoms of the syndrome such as muscle tremors, seizures and impaired coordination and movement. Critically, the researchers did not have to deliver healthy copies of the master gene to every affected cell in order to achieve positive results. In fact, the therapy only boosted the number of healthy gene copies from 50 percent to 65 percent. The authors believe that a further increase in the percentage of healthy cells would almost certainly produce even greater benefits. Extensive research is still needed before doctors would consider using gene therapy as a treatment for humans affected by Rett syndrome.