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Correspondence |

Cysteine as a Biomarker for Obstructive Sleep ApneaCysteine and Obstructive Sleep Apnea FREE TO VIEW

Saadah Alrajab, MD, MPH; Askin Uysal, MD; Christopher Jenks, MD
Author and Funding Information

From the Department of Pulmonary, Critical Care, and Sleep Medicine, Louisiana State University.

Correspondence to: Saadah Alrajab, MD, MPH, Louisiana State University, Department of Pulmonary, Critical Care, and Sleep Medicine, 1501 Kings Hwy, PO Box 33932, Shreveport, LA 71130; e-mail: salraj@lsuhsc.edu


Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (http://www.chestpubs.org/site/misc/reprints.xhtml).


© 2011 American College of Chest Physicians


Chest. 2011;140(1):268. doi:10.1378/chest.11-0334
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To the Editor:

In a recent study in CHEST (February 2011), Cintra and colleagues1 nicely demonstrated the relationship between obstructive sleep apnea (OSA) and cysteine. In their study, cysteine levels were significantly elevated in patients with OSA regardless of their BMI, compared with the control group. Effective treatment of OSA with continuous positive airway pressure (CPAP) resulted in a significant reduction in cysteine levels. We congratulate the authors on their well-designed study and success in introducing a novel marker to the field of sleep apnea. However, we have some concerns:

  • Tobacco smoking, hypertension, and a history of arterial atherosclerosis are known risk factors that are associated with elevated cysteine levels with, or even without, associated elevation in plasma homocysteine levels.2 Tobacco smoking, a major determinant of plasma cysteine level, was included in the exclusion criteria in this study. Hypertension and atherosclerosis could still be considered results of OSA, and, hence, higher cysteine levels could be considered a result of these conditions, not OSA.

  • Cysteine levels can be affected by many other conditions, mostly associated with OSA, such as hypertension, atherosclerosis, age, and creatinine level. Hence, it is not specific for sleep apnea, unless those conditions are excluded before the measurement.

  • A plausible explanation of hypercysteinemia in a patient with OSA is not provided in the study. If this marker is related to tissue hypoxemia, then patients with central sleep apnea, chronic respiratory failure by other causes, congestive heart failure, and possibly severe anemia would be associated with high cysteine levels.

A reproduction of this study’s results in a large, randomized, controlled study with measurement of cysteine levels (and maybe other candidate markers) before and after CPAP treatment and demonstration of relapse after discontinuation of CPAP is needed. This will also provide information about a good cutoff value for this marker if deemed reproducible. A good marker in OSA will have the ability to reduce the need for expensive polysomnography as a screening tool or possibly help monitor response to, and/or compliance with, CPAP treatment. So far, cysteine lacks specificity and does not fulfill those objectives.

Cintra F, Tufik S, D’Almeida V, et al. Cysteine: a potential biomarker for obstructive sleep apnea. Chest. 2011;1392:246-252. [CrossRef] [PubMed]
 
Brattström L, Lindgren A, Israelsson B, Andersson A, Hultberg B. Homocysteine and cysteine: determinants of plasma levels in middle-aged and elderly subjects. J Intern Med. 1994;2366:633-641. [CrossRef] [PubMed]
 

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References

Cintra F, Tufik S, D’Almeida V, et al. Cysteine: a potential biomarker for obstructive sleep apnea. Chest. 2011;1392:246-252. [CrossRef] [PubMed]
 
Brattström L, Lindgren A, Israelsson B, Andersson A, Hultberg B. Homocysteine and cysteine: determinants of plasma levels in middle-aged and elderly subjects. J Intern Med. 1994;2366:633-641. [CrossRef] [PubMed]
 
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