Despite the identification of gene mutations in methyl CpG binding protein 2 (MECP2) being linked to Rett syndrome (RS), research has been hindered by the lack of commercially available reference materials. Through collaboration between the Centers for Disease Control and Prevention (CDC) and members of the clinical-laboratory and non-profit–research communities, 35 DNA samples containing many common RS genetic variants have now been characterized and made publicly available, eliminating a major stumbling-block for investigators and opening the possibility of earlier, more accurate diagnosis of Rett syndrome, reports The Journal of Molecular Diagnostics.
The study was conducted via the CDC Genetic Testing Reference Materials Coordination Program (GeT-RM), which aims to help the genetic testing community obtain appropriate and well-defined reference materials for inherited genetic disorders, including cancer and infectious diseases. Researchers selected eight cell lines from RS patients already available from the National Institute of General Medical Sciences’ Coriell Cell Repository, which contained six of the most common mutations that cause RS, as well as one additional point mutation. In addition, DNA was obtained from 27 newly established cell lines derived from blood samples from Rett patients, which included a number of other MECP2 variants. Two of the samples were from males.
The samples were sent for DNA sequence and deletion/duplication analyses (using MLPA, semi-quantitative PCR, or array) to College of American Pathologist–accredited clinical genetic testing laboratories, and each sample was tested in between two to five laboratories. The investigators found that the results were concordant among laboratories and assay platforms.
“The panel of 35 publicly available genomic DNA samples developed and characterized as part of this study contains a wide variety of point mutations, deletions, and duplications in both male and female samples that can be used by clinical laboratories to ensure the quality of Rett syndrome testing,” asserts Dr. Kalman.
Point mutations or deletions/insertions of the MECP2 gene, which regulates aspects of brain development as well as the expression of other genes, were discovered to be associated with most cases of RS in 1999. However, since there are still no FDA-approved assays for Rett syndrome, laboratories have developed their own tests but need reference materials to standardize their techniques, validate assays, and meet regulatory and accreditation requirements. Ideally, the reference materials should be well characterized and contain the variants most commonly seen in RS patients.
What is Rett syndrome?
Rett syndrome is a neurodevelopmenal disorder that affects girls almost exclusively. It is characterized by normal early growth and development followed by a slowing of development, loss of purposeful use of the hands, distinctive hand movements, slowed brain and head growth, problems with walking, seizures, and intellectual disability.
The disorder was identified by Dr. Andreas Rett, an Austrian physician who first described it in a journal article in 1966. It was not until after a second article about the disorder, published in 1983 by Swedish researcher Dr. Bengt Hagberg, that the disorder was generally recognized.
The course of Rett syndrome, including the age of onset and the severity of symptoms, varies from child to child. Before the symptoms begin, however, the child generally appears to grow and develop normally, although there are often subtle abnormalities even in early infancy, such as loss of muscle tone (hypotonia), difficulty feeding, and jerkiness in limb movements. Then, gradually, mental and physical symptoms appear. As the syndrome progresses, the child loses purposeful use of her hands and the ability to speak. Other early symptoms may include problems crawling or walking and diminished eye contact. The loss of functional use of the hands is followed by compulsive hand movements such as wringing and washing. The onset of this period of regression is sometimes sudden.
Apraxia - the inability to perform motor functions - is perhaps the most severely disabling feature of Rett syndrome, interfering with every body movement, including eye gaze and speech.
Children with Rett syndrome often exhibit autistic-like behaviors in the early stages. Other symptoms may include walking on the toes, sleep problems, a wide-based gait, teeth grinding and difficulty chewing, slowed growth, seizures, cognitive disabilities, and breathing difficulties while awake such as hyperventilation, apnea (breath holding), and air swallowing.
“The availability of a renewable source of characterized reference materials for Rett syndrome will help to ensure the accuracy of these genetic tests and facilitate research and test development,” comments Lisa Kalman, PhD, of the Division of Laboratory Programs, Standards, and Services at the Centers for Disease Control and Prevention.
“Molecular diagnosis of Rett syndrome is performed by examination of patient DNA for MECP2 mutations using a variety of molecular diagnostic methods,” explains Dr. Kalman. “Genetic testing can help to confirm or establish the diagnosis of RS, especially when patients are young and the phenotype may not be completely apparent. Testing may also be important for at-risk relatives, prenatal diagnosis, or evaluation of an embryo prior to implantation during in vitro fertilization.”
Who Gets Rett Syndrome?
Rett syndrome is an autism spectrum disorder that affects girls almost exclusively. It’s rare—only about one in 10,000 to 15,000 girls will develop the condition.
In most cases of Rett syndrome, a child develops normally in early life. Between 6 and 18 months of age, though, changes in the normal patterns of mental and social development begin.
What Are the Symptoms of Rett Syndrome?
Although it’s not always detected, a slowing of head growth is one of the first events in Rett syndrome. Loss of muscle tone is also an initial symptom. Soon, the child loses any purposeful use of her hands. Instead, she habitually wrings or rubs her hands together.
Around 1 to 4 years of age, social and language skills deteriorate in a girl with Rett syndrome. She stops talking and develops extreme social anxiety and withdrawal or disinterest in other people.
Rett syndrome also causes problems with muscles and coordination. Walking becomes awkward as girls develop a jerky, stiff-legged gait. A girl with Rett syndrome may also have uncoordinated breathing and seizures.
What Causes Rett Syndrome?
Most children with Rett syndrome have a mutation in a particular gene on the X chromosome. Exactly what this gene does, or how its mutation leads to Rett syndrome, isn’t clear. It’s believed that the single gene may influence many other genes involved in development.
Although Rett syndrome seems to be genetic, the faulty gene is almost never inherited from the parents. Rather, it’s a chance mutation that happens in the girl’s own DNA. No Rett syndrome risk factors have been identified, other than being female. There is no known method for preventing Rett syndrome.
When boys develop the Rett syndrome mutation, they die shortly after birth. Because boys have only one X chromosome (instead of the two girls have), the disease is more serious, and quickly fatal.
Rett syndrome, a dominant X-linked neurodevelopmental disorder that primarily affects girls, occurs in one of every 10,000 to 15,000 live births. Girls with RS first appear to grow and develop normally, but between the ages of 1 and 4 years start to exhibit development delays, loss of purposeful use of the hands, slowed brain and head growth, and motor difficulties. In later stages, affected individuals may develop a spectrum of symptoms with varying severity, including muscle weakness, rigidity, spasticity, abnormal posturing, inability to speak, seizures, and repetitive hand movements such as wringing or washing.
Elsevier Health Sciences