Huntington's Disease Protein Quantified in Cerebrospinal Fluid

An immunoassay has been able to measure for the first time the build-up of a harmful mutant protein in the nervous system of patients during the progression of Huntington's disease (HD).

This neoteric assay will enable the testing of drugs that aim to lower the production of the pathogenic mutant huntingtin protein that causes the disease, and could be useful in predicting or monitoring the progression of HD. This genetic neurodegenerative disease usually develops in adulthood and causes abnormal involuntary movements, psychiatric symptoms, and dementia. It is caused by a single gene mutation that results in the production of mutant huntingtin protein.

An international team of scientists led by those at the University College London (UK) developed an ultrasensitive single-molecule counting mutant huntingtin protein (mHTT) immunoassay. The assay was used to quantify mHTT levels in cerebrospinal fluid (CSF) samples from individuals bearing the HD mutation and from control individuals in two independent cohorts. CSF and blood samples were collected from 12 individuals in London and 40 in Vancouver.

A single-molecule counting (SMC) immunoassay was used for mutant HTT protein quantification in CSF and plasma. This test was analyzed with the Erenna Immunoassay System (Singulex; Alameda, CA, USA). An antibody specifically against the polyglutamine domain of HTT was developed. Total protein, hemoglobin and tau proteins were also measured. Recombinant human proteins containing the N-terminal sequence of HTT with 548 amino acids (N548) and polyglutamine repeats of different lengths were generated for the study.

The investigators were able to detect mHTT protein in the CSF samples: mHTT was present in the CSF of almost all HTT mutation carriers, but not in that of control volunteers. In the London cohort, they were able to detect 182.5 ± 106.3 femtomolar (fM) mHTT in the CSF of all nine mutation carriers, but not in the CSF of any of the three controls. In the more diverse Vancouver cohort, they detected 289.1 ± 194.6 fM mHTT in the CSFs of 26 of 28 HTT mutation carriers, but not in any of the 10 controls.

Douglas Macdonald, PhD, a senior author of the study, said, “We do not yet have treatments that can slow the progression of Huntington's disease but, when we do, measuring the mutant protein in CSF could guide clinical decisions such as the best time to start a treatment. Measuring the amount of huntingtin may also be an essential biomarker for the upcoming trials of huntingtin-lowering therapeutics.” The study was published on April 6, 2015, in the Journal of Clinical Investigation.

Related Links:
University College London
Singulex