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

August 29, 2013, Massachusetts General Hospital

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

Research reveals atomic-level changes in ALS-linked protein

January 18, 2018
For the first time, researchers have described atom-by-atom changes in a family of proteins linked to amyotrophic lateral sclerosis (ALS), a group of brain disorders known as frontotemporal dementia and degenerative diseases ...

Fragile X finding shows normal neurons that interact poorly

January 18, 2018
Neurons in mice afflicted with the genetic defect that causes Fragile X syndrome (FXS) appear similar to those in healthy mice, but these neurons fail to interact normally, resulting in the long-known cognitive impairments, ...

How your brain remembers what you had for dinner last night

January 17, 2018
Confirming earlier computational models, researchers at University of California San Diego and UC San Diego School of Medicine, with colleagues in Arizona and Louisiana, report that episodic memories are encoded in the hippocampus ...

Recording a thought's fleeting trip through the brain

January 17, 2018
University of California, Berkeley neuroscientists have tracked the progress of a thought through the brain, showing clearly how the prefrontal cortex at the front of the brain coordinates activity to help us act in response ...

Midbrain 'start neurons' control whether we walk or run

January 17, 2018
Locomotion comprises the most fundamental movements we perform. It is a complex sequence from initiating the first step, to stopping when we reach our goal. At the same time, locomotion is executed at different speeds to ...

Neuroscientists suggest a model for how we gain volitional control of what we hold in our minds

January 16, 2018
Working memory is a sort of "mental sketchpad" that allows you to accomplish everyday tasks such as calling in your hungry family's takeout order and finding the bathroom you were just told "will be the third door on the ...

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.