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Figure.
Plasma levels of valine, leucine, and isoleucine in presymptomatic individuals (mean [SD] Unified Huntington Disease Rating Scale [UHDRS] score, 0.3 [0.9]) and patients at a mild (mean [SD] UHDRS score, 14.1 [6.5]), moderate (mean [SD] UHDRS score, 38.9 [6.9]), or severe (mean [SD] UHDRS score, 68.9 [15.3]) stage of disease compared with controls. Circles and triangles denote outliers that are farther than 1.5 and 3 interquartile ranges respectively from the nearer edge of the box. *P < .05; †P < .001.

Plasma levels of valine, leucine, and isoleucine in presymptomatic individuals (mean [SD] Unified Huntington Disease Rating Scale [UHDRS] score, 0.3 [0.9]) and patients at a mild (mean [SD] UHDRS score, 14.1 [6.5]), moderate (mean [SD] UHDRS score, 38.9 [6.9]), or severe (mean [SD] UHDRS score, 68.9 [15.3]) stage of disease compared with controls. Circles and triangles denote outliers that are farther than 1.5 and 3 interquartile ranges respectively from the nearer edge of the box. *P < .05; †P < .001.

1.
Mochel  FCharles  PSeguin  F  et al.  Early energy deficit in Huntington disease: identification of a plasma biomarker traceable during disease progression. PLoS One 2007;2 (7) e647
PubMedArticle
2.
Flier  JS Neuroscience: regulating energy balance: the substrate strikes back. Science 2006;312 (5775) 861- 864
PubMedArticle
3.
Hay  NSonenberg  N Upstream and downstream of mTOR. Genes Dev 2004;18 (16) 1926- 1945
PubMedArticle
4.
Colin  ERégulier  EPerrin  V  et al.  Akt is altered in an animal model of Huntington's disease and in patients. Eur J Neurosci 2005;21 (6) 1478- 1488
PubMedArticle
5.
Heng  MYDuong  DKAlbin  RL  et al.  Early autophagic response in a novel knock-in model of Huntington disease. Hum Mol Genet 2010;19 (19) 3702- 3720
PubMedArticle
Research Letters
February 2011

Validation of Plasma Branched Chain Amino Acids as Biomarkers in Huntington Disease

Author Affiliations

Author Affiliations: Université Pierre et Marie Curie, Institut National de la Santé et de la Recherche Médicale (INSERM), Unité Mixte de Recherche (UMR) S975/Centre National de la Recherche Scientifique, UMR 7225, Centre de Recherche Institut du Cerveau et de la Moelle (Drs Mochel and Durr); Assistance-Publique-Hôpitaux de Paris, Département de Génétique et Cytogénétique, Hôpital de La Salpêtrière (Drs Mochel and Durr and Ms Benaich); and Laboratoire de Biochimie Métabolique, Hôpital Necker-Enfants Malades (Dr Rabier), Paris, France.

Arch Neurol. 2011;68(2):264-271. doi:10.1001/archneurol.2010.358

While investigating body weight in a cohort of 32 patients at an early stage of Huntington disease (HD) and presymptomatic HD gene carriers, we found a significant decrease in the plasma branched-chain amino acids (BCAA) valine, leucine, and isoleucine in the HD group compared with 21 healthy controls. This systemic metabolic defect, which is indicative of hypercatabolism, was associated with early body weight loss in the HD group.1 We wanted to (1) try to replicate our initial findings in a larger HD cohort, and (2) assess the feasibility of using plasma BCAA as a biomarker in HD, ie, in a less controlled research environment than the initial study.1

Methods

After approval by the institutional ethics committees (Institut National de la Santé et de la Recherche Médicale, Recherche Biomédicale 03-48), we measured fasting levels of plasma BCAA as previously described1 in 16 presymptomatic HD gene carriers and 70 patients with HD at a mild, moderate, or severe stage of the disease who were seen consecutively at our outpatient clinic. Our control group consisted of 21 healthy individuals, previously described.1 To evaluate the multivariate associations, the LASSO (Least Absolute Shrinkage and Selection Operator) model selection technique was used with the adjusted r2 statistic as the model selection criterion. The number of CAG codons was forced into these models with the Unified Huntington Disease Rating Scale (UHDRS), age, body mass index (BMI; calculated as weight in kilograms divided by height in meters squared), sex, and their 2-way interactions as possible covariates.

Results

Plasma valine, leucine, and isoleucine levels were significantly lower in the HD group compared with controls (P = .02, <.001, and .002, respectively). In addition, we found a significant decrease of valine, leucine, and isoleucine in moderately affected patients and patients at a severe stage of the disease (Figure). Leucine was also significantly decreased in patients at a very mild stage of the disease and in presymptomatic individuals (Figure). Simple linear regression showed that plasma BCAA were not correlated with the UHDRS. However, we found that valine was negatively correlated with the number of CAG repeats (P = .01, adjusted r2 = 0.086). After adjusting for BMI and sex, we confirmed that there was a negative association between valine and CAG repeats (P = .02, adjusted r2 = 0.309). For every 1-unit increase in CAG, valine decreased by −3.33. We also found a significant association between leucine and CAG repeats (P = .04, adjusted r2 = 0.372), with an association dependent on BMI due to the interaction. For every 1-unit increase in CAG, leucine decreased by −1.50 for the mean value of BMI (23.2).

Comment

We confirmed, in a larger cohort of patients with HD at different stages of the disease as well as presymptomatic HD gene carriers sampled consecutively, that plasma BCAA are relevant and accessible biomarkers in HD. After adjusting for BMI and sex, we showed an inverse correlation between the plasma levels of valine and leucine and number of CAG repeats, the primary determinant of HD severity. Of the 3 BCAA, leucine was of particular interest because it was significantly reduced in patients at an early stage of the disease and, more remarkably, in presymptomatic individuals. Leucine is a well-known activator of mTor (mammalian target of rapamycin),2 which regulates protein synthesis and whose inhibition results in increased autophagic proteolysis.3 Akt, which has been shown to be altered in HD rat brain and in peripheral blood cells of patients with HD,4 also mediates the activity of mTor. Therefore, reduced leucine levels and altered Akt activation in HD may both result in mTor inhibition and exacerbation of proteolysis in HD.5 The significant correlation of BCAA with CAG repeats but not with UHDRS stages suggests that this biomarker is closely related to the primary defect in HD rather than to neuronal degeneration.

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Article Information

Correspondence: Dr Mochel, INSERM UMR S975, Department of Genetics, Hôpital de La Salpêtrière, 47 Boulevard de l'Hôpital, Bâtiment Nouvelle Pharmacie, 4ème étage, 75013 Paris, France (fanny.mochel@upmc.fr).

Financial Disclosure: None reported.

Additional Contributions: We wish to thank warmly the patients and presymptomatic individuals for their participation in this study. We are also thankful to Derek Blankenship, PhD, for statistical support.

References
1.
Mochel  FCharles  PSeguin  F  et al.  Early energy deficit in Huntington disease: identification of a plasma biomarker traceable during disease progression. PLoS One 2007;2 (7) e647
PubMedArticle
2.
Flier  JS Neuroscience: regulating energy balance: the substrate strikes back. Science 2006;312 (5775) 861- 864
PubMedArticle
3.
Hay  NSonenberg  N Upstream and downstream of mTOR. Genes Dev 2004;18 (16) 1926- 1945
PubMedArticle
4.
Colin  ERégulier  EPerrin  V  et al.  Akt is altered in an animal model of Huntington's disease and in patients. Eur J Neurosci 2005;21 (6) 1478- 1488
PubMedArticle
5.
Heng  MYDuong  DKAlbin  RL  et al.  Early autophagic response in a novel knock-in model of Huntington disease. Hum Mol Genet 2010;19 (19) 3702- 3720
PubMedArticle
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