High-risk populations include those with risk factors for stroke (eg, AF, refractory hypertension) and patients with stroke. The recommended screening includes a sleep his- tory (eg, snoring, witnessed apneas, daytime sleepiness), an evaluation of conditions that may occur as a consequence of sleep apnea (eg, motor vehicle accidents, stroke), and physi- cal examination (eg, BMI 35 kg/m2 , neck circumference >17 in for men or 16 in for women). The Epworth Sleepiness and Berlin Questionnaire757 are tools for screening for sleep apnea. However, most clinical screening tests miss a significant proportion of patients.758 Patients who are con- sidered to be high risk on the basis of this screening should be referred for polysomnography.730 Sleep-Disordered Breathing: Summary and Gaps Sleep apnea independently contributes to risk of stroke, and increasing sleep apnea severity is associated with increas- ing risk. No prospective, randomized trial has evaluated the effectiveness of sleep apnea treatment for primary stroke prevention. Sleep-Disordered Breathing: Recommendations 1. Because of its association with stroke risk, screening for sleep apnea through a detailed history, includ- ing structured questionnaires such as the Epworth Sleepiness Scale and Berlin Questionnaire, physical examination, and, if indicated, polysomnography may be considered (Class IIb; Level of Evidence C). 2. Treatment of sleep apnea to reduce the risk of stroke may be reasonable, although its effectiveness for pri- mary prevention of stroke is unknown (Class IIb; Level of Evidence C). Hyperhomocysteinemia Homocysteine is an amino acid derived from the metabolism of the essential amino acid methionine. Increased plasma lev- els of homocysteine are often a consequence of reduced enzy- matic activity in its metabolic pathways. 