Assay shown to be effective in measuring levels of mutant huntingtin protein

August 29, 2013

An assay designed to measure normal and abnormal forms of the huntingtin protein – the mutated form of which causes Huntington's disease (HD) – was successful in detecting levels of the mutant protein in a large multicenter study of individuals at risk for the devastating neurological disorder. The report from a team of Massachusetts General Hospital (MGH) investigators – which will appear in the Sept. 24 issue of Neurology and has been released online – also found changes in levels of the mutated protein that might predict when symptoms will appear.

"Our validation of this for measuring the in the blood of individuals with HD supports its usefulness in monitoring treatments designed to affect the mutant protein," says Steven Hersch, MD, PhD, of the MassGeneral Institute for Neurodegenerative Disease (MGH-MIND), senior author of the report. "Our results also suggest that this assay might sense biological stresses in the body that occur as the disease becomes symptomatic in individuals who have inherited the HD mutation."

Inheriting a single mutated copy of the causes deposition of the abnormal form of the protein within the brain. The of the eventually produce symptoms such as uncontrolled movements, erratic emotions and . Symptoms of HD usually first appear in the middle years and worsen over the 10- to 30-year course of the disorder, leading to death from a variety of complications. A genetic test for the HD mutation has been available since the gene was discovered at MGH more that 20 years ago, but since there currently is no way to delay or slow the progression of symptoms, many individuals at risk for the disorder choose not to learn their gene status. Several potential therapies in development are designed to reduce levels of mutant huntingtin, but studies are currently hampered by difficulty in assessing the drugs' effectiveness, especially in early-phase trials.

Several years ago a collaboration led by Anne Young, MD, PhD, former chief of Neurology at MGH and a co-author of the Neurology paper, developed the assay used in the current study. The assay uses what is called HTRF technology and a set of three antibodies against the huntingtin protein – including one specific for the mutation site – to measure the relative levels of the mutant and total huntingtin proteins. Previous studies have confirmed the ability of HTRF assay to measure normal and mutant huntingtin in animal models of the disease and in blood cells and brain tissue samples from HD patients.

The current study was designed to validate those results in a large multicenter study of presymptomatic individuals known to be at risk for the disease as well as in patients with early symptoms. The researchers analyzed white blood cells collected from participants in PHAROS (Prospective Huntington At-Risk Observational Study). This National Institutes of Health investigation – led by Young and Ira Shoulson, MD, of Georgetown University, also a coauthor of the current study – was conducted from 1999 to 2009 and enrolled 1,000 individuals who had a parent or sibling with the disorder but had not learned their gene status. Blood samples from 342 participants, collected at 35 centers around the U.S., were suitable for analysis with the HTRF assay.

The researchers determined that 228 participants had 36 or fewer CAG repeats – repetitions of a particular nucleotide sequence within the huntingtin gene – indicating the normal form of the gene. The other 114, including 26 who had developed symptoms during the course of PHAROS, had 37 or more repeats, reflecting the HD mutation. Among participants with expanded CAG repeats, the HTRF assay signal for mutant huntingtin was significantly stronger than among those with normal CAG repeats. In participants with CAG expansion, analyzing HTRF results in relation to either the estimated time to symptom onset or the time when symptoms appeared suggested that assay results might change with the appearance of symptoms.

"These findings raise the possibility that this assay could help predict symptom onset or progression; however, a long-term study that follows a group of participants as their symptoms appear and progress is needed to confirm this," says Hersch. "Right now we can use the assay in clinical trials to measure whether experimental treatments affect levels of mutant huntingtin in blood, an indicator that they may be working as hoped. Eventually we should be able to ask whether reduced blood levels, as measured by HTRF, correspond to an effective treatment for HD."

Study lead author Miriam Moscovitch-Lopatin, PhD, also of MGH-MIND, adds, "The extensive and consistent quality controls at the clinical sites, as well as those applied by our team in processing blood samples and performing the HTRF assay, were essential for the success of this study and will be vital for the future use of the assay." She is an instructor in Neurology, and Hersch is a professor of Neurology at Harvard Medical School.

Explore further: Toxic protein build-up in blood shines light on Huntington's disease

Related Stories

Toxic protein build-up in blood shines light on Huntington's disease

September 17, 2012
A new light-based technique for measuring levels of the toxic protein that causes Huntington's disease (HD) has been used to demonstrate that the protein builds up gradually in blood cells. Published today in the Journal ...

Immune cell migration is impeded in Huntington's disease

November 19, 2012
Huntington disease (HD) is an incurable neurodegenerative disease caused by a mutation in the huntingtin gene (htt). Though most of the symptoms of HD are neurological, the mutant HTT protein is expressed in non-neural cells ...

Scientists tackle Huntington's disease by targeting mutant gene

November 6, 2012
Huntington's disease is an inherited, neurodegenerative disorder that usually appears in mid-adult life and leads to uncoordinated body movements and cognitive decline. The disease is due to multiple repetitions of a deoxyribonucleic ...

Enzyme inhibition protects against Huntington's disease damage in two animal models

November 29, 2012
Treatment with a novel agent that inhibits the activity of SIRT2, an enzyme that regulates many important cellular functions, reduced neurological damage, slowed the loss of motor function and extended survival in two animal ...

Regulatory enzyme overexpression may protect against neurodegeneration in Huntington's disease

December 18, 2011
Treatment that increases brain levels of an important regulatory enzyme may slow the loss of brain cells that characterizes Huntington's disease (HD) and other neurodegenerative disorders. In a report receiving advance online ...

Recommended for you

The neural codes for body movements

July 21, 2017
A small patch of neurons in the brain can encode the movements of many body parts, according to researchers in the laboratory of Caltech's Richard Andersen, James G. Boswell Professor of Neuroscience, Tianqiao and Chrissy ...

Faulty support cells disrupt communication in brains of people with schizophrenia

July 20, 2017
New research has identified the culprit behind the wiring problems in the brains of people with schizophrenia. When researchers transplanted human brain cells generated from individuals diagnosed with childhood-onset schizophrenia ...

Scientists reveal how patterns of brain activity direct specific body movements

July 20, 2017
New research by Columbia scientists offers fresh insight into how the brain tells the body to move, from simple behaviors like walking, to trained movements that may take years to master. The discovery in mice advances knowledge ...

Scientists discover combined sensory map for heat, humidity in fly brain

July 20, 2017
Northwestern University neuroscientists now can visualize how fruit flies sense and process humidity and temperature together through a "sensory map" within their brains, according to new research.

Team traces masculinization in mice to estrogen receptor in inhibitory neurons

July 20, 2017
Researchers at Cold Spring Harbor Laboratory (CSHL) have opened a black box in the brain whose contents explain one of the remarkable yet mysterious facts of life.

Speech language therapy delivered through the Internet leads to similar improvements as in-person treatment

July 20, 2017
Telerehabilitation helps healthcare professionals reach more patients in need, but some worry it doesn't offer the same quality of care as in-person treatment. This isn't the case, according to recent research by Baycrest.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.