Unexplained intellectual disability explained by state-of-the-art genetic analysis

November 08, 2012

A research team reported that next generation sequencing of the exome, the 1 to 2% of the DNA containing the genes that code for proteins, enabled the identification of the genetic causes of unexplained intellectual disability in over 50% of patients in a study conducted at Radboud University Medical Centre in Nijmegen, The Netherlands.

"Through next generation sequencing, we were able to discover mutations in genes that had not been previously linked to causing intellectual disability," said Marjolein Willemsen, M.D., Ph.D., who presented the research today (Nov. 8) at the American Society of Human Genetics 2012 meeting in San Francisco.

Correctly diagnosing children with intellectual disability (ID) can lead to early intervention and special education programs, vocational training and health screenings for associated conditions that will enable them to reach their full potential, said Dr. Willemsen of Radboud's department of human genetics.

Genetic diagnosis "is of major importance for the care and counseling of patients and families," Dr. Willemsen said. "Proper diagnosis provides insight into associated health and behavioral problems, prognosis and recurrence risk."

The cause of intellectual disability is unknown in more than half of patients with learning and other intellectual disabilities, which affect about 2% of the population, said Tjitske Kleefstra, M.D., Ph.D., also of Radboud University Medical Centre's human genetics department.

Participating in the Radboud University study were 253 patients with unexplained intellectual disability, most of whom were adults. They underwent a multidisciplinary clinical evaluation and a metabolic screen. Genome-wide analysis of each patient's DNA was also conducted, and specific genetic diagnostic tests were performed as needed.

Because they used both genetic tests and clinical evaluations, the researchers were able to correlate the biological as well as the behavioral features of each patient's intellectual disability with the DNA findings.

Intellectual disability can be a challenge to diagnose because a wide range of features characterizes these disorders, and the underlying genetic causes can vary widely, Dr. Kleefstra said. "As a result, many parents go from one doctor to another in search of a diagnosis and treatment for their child," she added.

In the first part of the study, a diagnosis was made in over 18% of the patients as a result of the combination of clinical evaluation and application of genetic diagnostic technologies that are now routinely used in clinical genetic practice.

Many of the identified mutations were chromosomal abnormalities, and 5% were mutations in single genes that already had been linked to ID. One of these genes, EHMT1, was discovered in 2006 by Dr. Kleefstra as the cause of what is now known as the Kleefstra syndrome, which is characterized by intellectual disability, hypotonia (low muscle tone) and distinctive facial appearance.

The researchers then performed next generation sequencing (NGS) in a subset of the patients who remained undiagnosed after the first analysis. In this second part of the study, the exomes of the included patients were analyzed.

In 17 of the 47 patients (36.2%) in whom NGS was applied, the likely pathogenic genetic causes were identified. The total yield of both parts of the study thus totaled over 54%.

Because intellectual disability syndromes caused by several novel genes were identified, the study has expanded scientific knowledge about the range of genetic causation in intellectual disability, Dr. Willemsen said.
-end-
The researchers' abstract is titled, "Making headway with the molecular and clinical definition of rare genetic disorders with intellectual disability."

About ASHG

The American Society of Human Genetics is the primary professional membership organization for nearly 8,000 human genetics specialists worldwide. The ASHG Annual Meeting is the world's largest gathering of human genetics professionals and a forum for renowned experts in the field.

American Society of Human Genetics

Related DNA Articles from Brightsurf:

A new twist on DNA origami
A team* of scientists from ASU and Shanghai Jiao Tong University (SJTU) led by Hao Yan, ASU's Milton Glick Professor in the School of Molecular Sciences, and director of the ASU Biodesign Institute's Center for Molecular Design and Biomimetics, has just announced the creation of a new type of meta-DNA structures that will open up the fields of optoelectronics (including information storage and encryption) as well as synthetic biology.

Solving a DNA mystery
''A watched pot never boils,'' as the saying goes, but that was not the case for UC Santa Barbara researchers watching a ''pot'' of liquids formed from DNA.

Junk DNA might be really, really useful for biocomputing
When you don't understand how things work, it's not unusual to think of them as just plain old junk.

Designing DNA from scratch: Engineering the functions of micrometer-sized DNA droplets
Scientists at Tokyo Institute of Technology (Tokyo Tech) have constructed ''DNA droplets'' comprising designed DNA nanostructures.

Does DNA in the water tell us how many fish are there?
Researchers have developed a new non-invasive method to count individual fish by measuring the concentration of environmental DNA in the water, which could be applied for quantitative monitoring of aquatic ecosystems.

Zigzag DNA
How the cell organizes DNA into tightly packed chromosomes. Nature publication by Delft University of Technology and EMBL Heidelberg.

Scientists now know what DNA's chaperone looks like
Researchers have discovered the structure of the FACT protein -- a mysterious protein central to the functioning of DNA.

DNA is like everything else: it's not what you have, but how you use it
A new paradigm for reading out genetic information in DNA is described by Dr.

A new spin on DNA
For decades, researchers have chased ways to study biological machines.

From face to DNA: New method aims to improve match between DNA sample and face database
Predicting what someone's face looks like based on a DNA sample remains a hard nut to crack for science.

Read More: DNA News and DNA Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.