These results contribute to the understanding of the natural history of coronary artery disease and are also of historical interest. The poor survival of patients with three-vessel disease and low ejection fractions continues to emphasize the importance of considering revascularization for these patients.

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SUMMARY The prevalence of coronary artery stenoses 2 70% or left main stenosis > 50% was evaluated in 20,391 patients who underwent angiography in the Coronary Artery Surgery Study from 1975-1979. After the patients with unstable angina or myocardial infarction were excluded, the disease prevalence in the 8157 patients with definite angina, probable angina, and nonspecific chest pain was 93%, 66% and 14% in men and 72%, 36% and 6% in women (p < 0.001).The age and sex of the patients and character of chest pain were important determinants of disease prevalence and severity. Left main or three-vessel coronary disease occurred in more than 50% of middle-aged men and older women with definite angina and in more than 50% of men who had probable angina and were older than 60 years of age. In contrast, left main coronary disease occurred in less than 2% of 1282 men and less than 1% of 1397 women with nonspecific chest pain regardless of age. In this latter patient subset, less than 5% of men and less than 1% of women in each decade under 60 years had left main or three-vessel coronary artery disease.Thus, high-risk coronary disease is common in middle-aged patients with definite angina and older patients with probable angina, but is rare in patients with nonspecific chest pain. Indications and guidelines for diagnostic noninvasive tests and coronary angiography could be based on these results.

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The accumulation of excessive quantities of sphingomyelin in tissues of patients with Niemann-Pick disease was demonstrated by Klenk in 19341, 2 and has been amply confirmed by other investigators.3-5 A study by Crocker and Mays6 indicated that the rate of biosynthesis of sphingomyelin in tissues from these patients appeared to be essentially normal. These findings suggested that the metabolic lesion in this condition might be of a catabolic nature. We have recently obtained evidence for the presence of a specific enzyme in liver tissue which catalyzes the hydrolysis of sphingomyelin.7 The enzyme was partially purified from rat liver tissue, and the products of the reaction were demonstrated to be phosphorylcholine and ceramide. The most highly purified enzyme preparations did not catalyze the hydrolysis of lecithin or phosphatidylethanolamine. Lecithin, however, appeared to be a competitive inhibitor of the reaction. Similar enzymatic activity could be detected in human liver tissue. The present report describes experiments in which the level of the sphingomyelin-cleaving enzyme in liver and kidney tissue obtained from six patients with the classic infantile form of Niemann-Pick disease8 is compared with the values found in a liver biopsy sample from a normal human adult and liver and kidney tissue of patients with various other disorders. Materials and Methods.-Sphingomyelin labeled with C14 in the methyl carbon atoms of the choline portion of the molecule was synthesized as described previously.7 Samples of liver and kidney tissue were homogenized in 10 vol of 0.25 M sucrose with an all-glass TenBroeck homogenizer and centrifuged at 600 X g for 12 min. Suitable aliquots of the supernatant suspensions were