A Mysterious Case of Stroke in Childhood
In 1933, an eight-year-old boy was admitted to the Massachusetts General Hospital for the evaluation of four days of headache, drowsiness and vomiting. The boy was of Irish-American-ancestry and exhibited signs of retarded mental development. The lenses of both of the boy's eyes were dislocated, a congenital defect which interfered with his vision. One of the boy's brothers had a similar defect. Two weeks before admission to the hospital, the eight-year-old had been evaluated in the orthopedic clinic for a limp. The cause was found to be coxa vara, a congenital abnormality of the bone in the hip joint, which caused the leg to be shortened. After admission to the hospital, the boy's condition deteriorated severely. There were signs of a stroke, especially weakness and abnormal reflexes on the left side of the body. The blood pressure and temperature became elevated, but there were no signs of infection. Nothing could be done to prevent further deterioration of the boy's condition, and he died three days later.
After analyzing the boy's tissues, the pathologist established that the cause of death was arteriosclerosis of the carotid artery with cerebral infarct (hardening of the artery leading to the brain with death of brain tissue).
This obscure case, referred to as Case 19471, was published in the November 23 issue of the New England Journal of Medicine in 1933' and was subsequently forgotten for 32 years even though the findings were provocative. An apparently inherited abnormality of unknown cause was responsible for the death of an eight-year-old boy from a disease of aging, arteriosclerosis and stroke, usually found only in the elderly.
Medical Sleuth Work
Thirty two years later, in 1965, a nine-year-old girl of Irish-American ancestry was evaluated at the pediatric clinic of the Massachusetts General Hospital because of slow mental development. The child's complexion was ruddy and flushed because of dilated blood vessels. The lenses of her eyes were dislocated, recalling several similar cases of a disease called homocystinuria, discovered just three years earlier in Belfast, Northern Ireland. These cases were identified by using new techniques to study the chemical composition of the urine of mentally retarded patients. In these cases, the urine was found to contain homocysteine, an amino acid derived from the normal breakdown of proteins in the body.
The young girl's mother told the pediatricians that an uncle had died suddenly of a similar disease in childhood over 30 years before and that the case was so unusual it was published in a medical journal. In searching the library, the pediatricians found the report describing Case 19471 in the November 23, 1933 issue of the New England Journal of Medicine. 1 This was the little girl's uncle.
The pediatricians took a sample of the young girl's urine to a laboratory for chemical analysis of amino acids, the basic building blocks of all the proteins of the body. By adding a few drops of the chemical sodium nitroprusside to detect homocysteine, the solution turned a deep magenta color. The test was positive for homocysteine.
By these laboratory tests the pediatricians verified that the nine-year-old girl with mental retardation had homo-cystinuria. They also concluded that her uncle, the eight-year-old boy who mysteriously died of a stroke in 1933, must also have had homocystinuria.
Cases of homocystinuria typically have mild mental retardation, tall stature, a ruddy complexion, light-colored hair and dislocation of the lenses of the eyes. The tall stature is caused by rapid growth in childhood, producing long legs, arms, fingers and toes. Many of the children with this disease die from blood clots developing in the brain, heart or kidneys, causing heart attack, stroke or kidney failure in childhood. The arteries in these cases are abnormal, with hardening and loss of elasticity of the artery walls.
"Chance Favors Only the Prepared Mind" — Louis Pasteur
In 1968 I had finally completed my many years of education, residency and fellowship in chemistry, medicine, biochemistry, molecular biology, genetics and pathology. After studying molecular genetics with the geneticist Guido Pontecorvo at Glasgow University in Scotland and with the discoverer of DNA structure, James Watson, at Harvard University, I completed my residency in pathology and was given an appointment and a research laboratory at Massachusetts General Hospital in Boston.
In order to study diseases of genetic origin, I decided to affiliate myself with the newly formed human genetics unit at the hospital. After several weeks of examining patients with genetic diseases, a case retrospectively diagnosed as ho-mocystinuria was presented by the pediatricians. The fascinating story was told of the eight-year-old boy who had died of a stroke 35 years earlier. I decided to look at the pathology of the case because of the unusual feature of death in childhood from a disease previously attributed to aging. Was there a connection between abnormal homocysteine formation, blood clots and blood vessel disease in this bov?
By chance, I had a background of knowledge about homocysteine and other amino acids containing sulfur. Several years previously I had worked on amino acids and protein formation in the liver with Dr. Giulio Cantoni at the National Institutes of Health in Bethesda. In 1952 Cantoni had discovered adenosyl methionine, an important trace substance that is required for protein formation and other chemical reactions in the body. He found that this compound is formed from ATP, the source of chemical energy in the body, and methionine, with the help of enzymes in the liver. Methionine is an amino acid containing sulfur that is found in all proteins. Proteins are made up of 20 different amino acid building blocks. Methionine is chemically closely related to homocysteine. Adenosyl methionine, Cantoni's compound, transfers a carbon atom in the form of a methyl group to the sulfur atom of homocysteine to form methionine. This complicated process was later found to require the action of vitamins B12 and folic acid. During my two years in Cantoni's laboratory there were lengthy discussions about how ad-enosyl methionine and homocysteine function in the body.
Studying Homocystinuria
I had not even heard of homocystinuria that day in 1968 when the pediatricians presented the story of the eight-year-old boy to the human genetics group. The disease had been discovered only six years earlier by medical investigators in Belfast, Northern Ireland. Simultaneously cases of homocystinuria were discovered in Madison, Wisconsin and in Philadelphia by George Spaeth, an ophthalmologist who was a classmate of mine from Harvard Medical School. Spaeth had discovered homocysteine in the urine of one of his patients with congenital dislocation of the lenses. Still another physician, Dr. Harvey Mudd, had studied several more of these cases in Cantoni's laboratory at the National Institutes of Health. Mudd and his associates had shown that in homocystinuria the liver is unable to dispose of homocysteine normally because of a genetic error in the liver enzyme cystathionine synthase.
Spaeth and his associates had found that in some patients with homocystinuria the amount of homocysteine in the urine was dramatically decreased by moderately large doses of vitamin B6. The liver enzyme that Mudd had shown was abnormal in homocystinuria cases requires vitamin B6 for normal activity. This enzyme normally converts homocysteine to cystathionine, which is further processed in the liver to cysteine, another sulfur amino acid, and sulfate, for eventual excretion in the urine.
Because I knew something about homocysteine from my experience in Cantoni's laboratory and because I wanted to use my new skills and knowledge as a pathologist, I decided to restudy the landmark case from 1933. After reading about it in the New England Journal of Medicine, I looked in the pathology department files for other data on the case. I found several original slides and a small lump of paraffin blocks containing tissues from the young boy. The blocks were melted together because they had been stored for many years in the hot attic of the old Allen Street building, long since demolished.
The paraffin blocks were remelted, separated and reprocessed by the pathology technicians to make a new set of glass slides for examination by microscopy. In viewing the slides, I confirmed what a pathologist had observed 35 years earlier. The walls of the carotid arteries leading to the brain were severely thickened and damaged by arteriosclerosis, a form of hardening of the arteries. Blood clots prevented blood from reaching the brain of the child, causing death of the right half of the brain.
This disastrous blood vessel disease had caused a stroke and killed the boy with what I now knew to be the newly discovered disease, homocystinuria. In addition to changes in the carotid arteries, I also found scattered, widespread changes in virtually all of the small arteries of the body. It was obvious to me that in some way the genetic error in this disease produced significant changes in all of the arteries. In addition, these changes looked to me, as a newly minted pathologist, very similar to the changes wrought by ordinary arteriosclerosis I had found in many of the elderly patients I saw during my residency.
There were many questions to be answered. How did I know that the hardening of the arteries was caused by the disease homocystinuria? Was there an effect on cholesterol and fat? Why was there no cholesterol deposited in the walls of the child's arteries? Was this disease of the blood vessels the same disease, arteriosclerosis, that is found in elderly people without homocystinuria? Did the genetic error in the liver enzyme of this child cause changes in other vital processes in the body? What had other medical scientists discovered about a connection between homocysteine and arteriosclerosis?
I learned that doctors in Belfast and in London had studied 10 cases of children affected by homocystinuria. 2 They found that many of these children had died from blood clots in the brain, heart and kidneys. They showed that hardening of the arteries resulting from fibrous plaques and loss of elasticity was of major importance in these cases and they considered that an indirect effect of abnormal methionine processing in the liver could have been the cause. Other doctors had found that the blood platelets, which contribute to blood clotting, are abnormally reactive in homocystinuria.
A group of doctors at Johns Hopkins Hospital in Baltimore also found that blood clots and thickening of the artery walls produced heart attacks and strokes in their patients with homocystinuria. 3 In describing the thickening of the artery walls, they also emphasized their severe loss of elasticity. Borrowing some of the slides from the cases from Belfast and from Johns Hopkins for comparison, I found that the changes in the arteries were identical to those in the 1933 case.
Neither group of doctors had used the term "arteriosclerosis" to describe the changes they found in the arteries of children with homocystinuria. Neither group related the changes in the arteries to the hardening of the arteries found in elderly people without homocystinuria. In fact, in the 1933 case, the pathologist had compared the changes in the arteries of the eight-year-old boy with the arteriosclerosis that he found in elderly patients without this inherited disease. By reading about these cases, it became obvious that children with homocystinuria have a severe disease of the arteries. It was not clear, however, how homocystinuria could produce changes in the arteries resembling arteriosclerosis without affecting cholesterol, lipoproteins or fats in the blood and in the artery walls.
Some time later, at a human genetics conference, a case of homocystinuria in a two-month-old baby boy was presented. The important difference from previous cases was that, in addition to homocysteine, this child was found to have another substance related to homocysteine, called cystathionine, in his urine. This finding indicated that the abnormality of the liver that was found in cases at the National Institutes of Health could not explain the liver abnormality in this baby.
By deciphering the baby's exact liver abnormality, the doctors discovered a new, previously unknown disease in which a different liver enzyme is abnormal. 4 This enzyme (methyltetrahydrofolate homocysteine methyl transferase) was unable to transform homocysteine into methionine using vitamin B12. A normal liver performs this conversion easily and rapidly. The new abnormality explained the presence of both homocystine and cystathionine in the baby's urine. In this boy the enzyme that is abnormal in other cases of homocystinuria was found to be normal, accounting for his liver's ability to produce cystathionine. Unfortunately, despite all of their efforts to treat the baby's disease with vitamin B12, vitamin B6, and another B vitamin, folic acid, he died within several days.
After hearing about the child, I immediately recalled the interesting case of homocystinuria documented in 1933, and decided to examine the autopsy protocol and tissue slides taken from the deceased baby. I predicted that the baby's blood vessels would show thickening of the artery walls caused by arteriosclerosis. If homocysteine, the amino acid itself, damages the arteries, the baby's arteries would manifest the same changes in the arteries as in the 1933 case. If the arteries were normal in the baby, then homocysteine must act indirectly to produce the arterial changes in patients with homocystinuria, 2 as doctors had theorized in 1965.
Rushing back to the pathology laboratory, I quickly located the report of the baby's autopsy. The protocol had been completed several weeks before, filed away and forgotten. I looked for the description of the arteries and was crestfallen to find that the report said nothing whatsoever about the arteries. To make matters worse, I knew that the resident who had completed the report was a very capable and conscientious doctor. However, some fat droplets were reported in the cells of the liver, and there were peculiar changes in the lining of the stomach. The resident's description of the biochemical abnormality in this new type of homocystinuria, 4 was detailed, accurate and well-written.
However, I was determined to find out what the baby's arteries looked like. Because of the severe liver disease and pneumonia in the lungs, the child had grown very little since birth and his organs were small. My fellow resident had carefully preserved all of the organs in a jar of formalin. I decided to restudy this case as carefully as I had studied the case from 1933. After the technicians had prepared a large collection of slides from the organs, I began to examine them carefully and systematically, making notes about the details of my findings.
Studying the arteries, I became very excited to discover that the changes of arteriosclerosis were there after all! Evidently my fellow resident had not examined the blood vessels carefully enough in preparing his autopsy report. He had not found severe damage to the arteries because he was not looking for these significant changes as I was.
I knew immediately that this discovery was extremely important and that I could investigate its significance because of my background of knowledge in biochemistry and molecular biology. I was so excited by this medical discovery that I had difficulty sleeping for almost two weeks. During that period, I woke up daily before sunrise thinking about what I had seen and how it related to my knowledge of homocysteine, arteriosclerosis and cholesterol. 1 had proven that in these rare genetic diseases, at least, the amino acid homocysteine caused damage and hardening of the arteries by a direct effect on the cells and tissues lining the arteries.
New Questions
If homocysteine causes damage to the arteries in children with rare inherited diseases, what does this discovery imply for the general population? In the 1950s and 1960s heart disease and stroke had reached epidemic proportions, becoming the number-one cause of death in America. Surely, the millions of people with heart disease could not all have rare inherited diseases that caused homocysteine to show up in the urine.
I wanted to find out how homocysteine is related to cholesterol and arteriosclerosis. The leading theory in 1968 was that a buildup of cholesterol in the "bad" form, low-density lipoprotein (LDL), somehow causes cholesterol to be deposited in the walls of the arteries. Both LDL and the "good" form of cholesterol, high-density lipoprotein (HDL), had been studied in the 1940s and 1950s at the University of California and at the National Institutes of Health in Bethesda. These studies had shown that a high level of LDL carried a high risk of developing heart disease. Similarly, a high level of HDL carried a degree of protection against developing heart disease. How does homocysteine fit into these theories?
Searching my memories from medical school, I recalled a lecture on the role of cholesterol in heart disease 13 years earlier, in 1955. At that time doctors at the Harvard School of Public Health had been studying cholesterol and experimental arteriosclerosis in monkeys. As I recalled, they had found that feeding the amino acid methionine to monkeys in a synthetic diet had caused the level of cholesterol in their blood to decline. 5 These investigators believed that this effect might have been beneficial in preventing cholesterol deposits from forming in the walls of the arteries. In contrast to this interpretation, I had found that a close chemical relative of methionine, homocysteine, was clearly causing damage to the arteries in children with homocystinuria.
A problem with the experiments with monkeys was that pure methionine was toxic when given in high doses. The animals lost weight, refused to eat normally and looked sickly. Because the animals could not eat their toxic diet, they could not eat the large amounts of cholesterol that were also included in it. When the monkeys' arteries were examined, no definite conclusion could be reached regarding whether methionine actually prevented or caused damage to the arteries. Because the doctors used a purified soy bean protein preparation, they believed that a deficiency of methionine could explain their results.
What was the effect of feeding homocysteine in its double form, homocystine, to experimental animals? Medical investigators at Duke University had done such a study in rats 6 several years earlier. They had found that, just as in the study in which methionine was fed to monkeys, homocystine in the diet caused the rats to lose weight and become sickly. Nothing was found in examining their tissues to suggest that homocystine damages the arteries in this type of experiment. The tissues looked like those of a starving animal except that deposits of iron were found in several organs. It was as if the added homocystine prevented the animals from eating altogether.
In discussing my findings and conclusions about homocysteine and arteriosclerosis with a biochemist colleague, we recalled a study of arteriosclerosis and vitamin B6 that had been published 20 years earlier. 7 Dr. James Rinehart and his associates at the University of California in San Francisco had published several papers showing that a partial deficiency of vitamin B6 in a synthetic diet fed to monkeys caused arteriosclerotic changes in the arteries if the experiment was carried out for a prolonged period, usually 6 to 18 months. Biochemists in Russia had discovered that the liver enzyme that converts homocysteine to cystathionine needs vitamin B6 for its action. Harvey Mudd had found that this enzyme is abnormal in children with homocystinuria. George Spaeth had found that some children with homocystinuria respond dramatically to moderately large doses of vitamin B6, preventing a buildup of homocysteine in their blood and urine. Could Rinehart's monkeys with vitamin B6 deficiency have had a buildup of homocysteine that damaged their arteries?
It was difficult to explain how homocysteine relates to cholesterol in causing damage to arteries. In the first place, the children with different types of homocystinuria had normal blood cholesterol levels. Secondly, Rinehart's monkeys with vitamin B6 deficiency and arteriosclerosis had normal cholesterol levels. Finally, the investigators at Harvard School of Public Health had repeated Rinehart's experiments with vitamin B6 deficiency in monkeys and had found no evidence of cholesterol deposits in the arteries. They had prepared a diet that was so deficient in vitamin B6 that their monkeys lost weight, became anemic and died within several months before changes in the arteries could be detected.
At about this time, I was asked to describe the pathological findings in an interesting case at a clinical pathology conference. The discussion was held in the Ether Dome, where in the 19th century ether had first been demonstrated publicly for surgical anesthesia. This was also the auditorium where 35 years earlier the case of the eight-year-old boy with arteriosclerosis (and later identified as homocystinuria) had been discussed. During the conference, a visiting cardiologist from South Africa, Dr. Moses Suzman, asked several interesting questions about my discussion of the pathological findings.
After the conference I met and chatted with Dr. Suzman, who was interested in my study of arteriosclerosis in children with homocystinuria. By this time, I was preparing my findings for publication in the American Journal of Pathology. Dr. Suzman told me that he knew James Rinehart when they were both research fellows at the Boston City Hospital. Rinehart had been trying to produce cirrhosis of the liver in monkeys by making them deficient in various vitamins. His experiments initially failed to produce cirrhosis, but he discovered that vitamin B6 deficiency caused arteriosclerosis if carried out for long enough periods of time. Dr. Suzman told me that in his practice in South Africa he routinely gave vitamin B6 and other vitamins to his cardiac patients because of Rine-hart's discovery. Using this approach, Suzman's patients did extremely well, losing their symptoms of chest pain on exertion, increasing their exercise tolerance, improving their electrocardiograms and their diabetes and reducing their risk of heart attack.
Publication
In preparing my study for publication, I read several articles by doctors from Toronto who had been working with choline, trying to understand how this substance influences fat buildup in the liver. They had found that a deficiency of choline in the diet of rats caused arteriosclerotic changes in the rats' arteries and fat buildup in the liver. 8 Choline, a component of lecithin, was the same substance that had been studied in the 1930s, when it was learned that choline supplemented homocysteine in replacing methionine in growth experiments with animals. This finding of arteriosclerosis from choline deficiency raised the possibility that the arteriosclerotic changes were caused by a buildup of homocysteine in the rats' blood.
In the original publication of my medical discovery on homocysteine and arteriosclerosis, I concluded that homocysteine damages the arteries by a direct effect on the arterial cells and tissues of children with homocystinuria caused by two different genetic defects. 9 I went on to pose the question, "Is it possible, for example, that in patients with hereditary, dietary, environmental or other predisposition to arteriosclerosis—such as that observed in those who have diabetes, hypothyroidism, hypertension, radiation injury or who smoke cigarettes—damage to the arteries develops as the result of homocysteine build-up?" Finally I hypothesized that arteriosclerosis was caused by elevated blood homocysteine levels that were presumed to occur in vitamin B6-deficient monkeys and in choline-deficient rats.
It seemed obvious to me that this discovery was of tremendous potential importance in understanding the basic cause of arteriosclerosis in the general population. When I sent the manuscript for publication in 1969, it was accepted by the editor immediately without changes. I was astonished to receive hundreds of requests for reprints of this paper in succeeding weeks. Evidently, there were medical scientists all over the world who were interested in a new approach to understanding heart disease and arteriosclerosis.
Confirmation of the Discovery
Following the discovery of a significant new scientific or medical observation and interpretation, a period of questioning inevitably ensues. Other investigators who are knowledgeable in the field need time to read and understand the potential significance of the new observation. During the period of questioning, several basic issues are considered by other scientists. First and foremost, is the basic observation correct and valid? Second, is there independent evidence from a distinct but related set of observations that confirms the basic observation? Third, is the interpretation of the significance of the new observation reasonable and in accordance with other principles of medical science? Finally, do the basic observation and its interpretation suggest other independent means of proof and confirmation of the new discovery?
The essence of the new discovery in the case of homocysteine and vascular disease is the interpretation that, regardless of its cause, elevation of blood homocysteine causes arteriosclerosis by damaging the cells and tissues of the arteries. In the most frequently encountered form of homocystinuria, an abnormal liver enzyme (cystathionine synthase) causes elevation of blood homocysteine because the conversion of homocysteine to cystathionine (transsul-furation) is blocked. Damage to the arteries and arteriosclerotic changes in this disease were well described in the 1933 case 1 and in the cases from Belfast 2 and from Johns Hopkins. 3
The form of homocystinuria caused by the abnormal liver enzyme (methyltetrahydrofolate homocysteine methyl transferase) that uses folic acid and vitamin B12 to convert homocysteine to methionine is much rarer. The first case in the world literature 4 of this form of homocystinuria (cobalamin C disease) was the key case that led to my discovery of the damaging effect of homocysteine on artery walls. 9 Because of its rarity, several years passed before the changes in the blood vessels in a second case were reported. 10 In this case, the changes in small blood vessels, especially arterioles, were found only in the brain. Nevertheless, this case was important because it confirmed my basic observation of arterial damage in the first reported case. Another five years passed before similar arterial damage was found in a third case (from Switzerland) of this rare form of homocystinuria. 11 These cases are important because they confirmed the basic observation that I had reported in 1969.
Another even more significant confirmation of my discovery of the relation between homocysteine and vascular disease was described in a third type of homocystinuria. 12 In this disease an abnormal liver enzyme (methylenetet-rahydrofolate reductase) fails to convert folic acid to the form that is required for conversion of homocysteine to methionine by remethylation. In this case (from Chicago) damage to the arteries and arteriosclerosis were found to be virtually identical with that found in the other two types of homocystinuria. This independent confirmation of the connection between elevated blood homocysteine, vascular damage and arteriosclerosis in a third type of homocystinuria is particularly significant. This finding enabled one to conclude that in all of the three principle types of inherited homocystinuria, elevation of blood homocysteine causes arterial damage and arteriosclerosis regardless of the particular liver enzyme that is abnormal. In the most frequent form of homocystinuria, cystathionine synthase deficiency, vitamin B6 is effective in correcting the abnormal metabolism of methionine and preventing elevation of blood homocysteine in about one-half of the cases. In the next most frequent form of homocystinuria, methyl-enetetrahydrofolate reductase deficiency, the B vitamin folic acid corrects the metabolic abnormality and prevents elevation of blood homocysteine in some cases. In the rarest form of homocystinuria, methyl transferase deficiency, vitamin B12 usually has little effect on the metabolic abnormality because of difficulties with absorption and function of vitamin B12 in the liver. In two of these three different types of an uncommon genetic disease, at least, therapy with specific vitamins offers some promise of preventing the arteriosclerosis associated with elevated blood homocysteine levels.
Questions and Initial Reaction
Is elevation of blood homocysteine significant to individuals with arteriosclerosis in the general population who do not have a form of homocystinuria? Is it possible that otherwise normal individuals may carry a silent genetic defect in the heterozygous form of a homocystinuria gene that may predispose them to elevation of blood homocysteine? Does the homocysteine approach imply that large segments of the population may have partial deficiencies of vitamins B6, B12 and folic acid? Is therapy with B vitamins a reasonable approach to prevention or treatment of arteriosclerosis in the general population? Can these provocative observations on the cause of arteriosclerosis in rare genetic diseases suggest ways to prove and to confirm the basic medical discovery by other independent means? What is the significance of homocysteine in regard to the cholesterol/lipid theory of causation of arteriosclerosis?
The initial reaction to my publication and lectures about the relation of homocysteine to arteriosclerosis took different forms according to the interest of the readers or audience. There was cautious acceptance of the idea that elevation of blood homocysteine was in some way the cause of vascular disease in the patients with homocystinuria. However, there was doubt that the vascular disease was indeed identical with arteriosclerosis as it is seen in the general population. In particular, the failure to find cholesterol crystals or lipid deposits in the arteries or elevation of blood cholesterol in children with homocystinuria made it especially troublesome for many to accept this discovery as relevant to arteriosclerosis as it is more commonly found. Finally, the suggestion that an amino acid, rather than cholesterol or fat, could be atherogenic, actually causing arteriosclerotic plaques, seemed difficult for many experts to accept.
Among those doctors and medical scientists who responded directly to publication of the discovery, several had specific knowledge about amino acid metabolism and vitamins B6, B12 or folic acid in disease processes. Several logical questions were asked about the effect of homocysteine on cells, tissues and metabolic processes in general. For example, there was an excellent question about whether the drug isoniazide could exacerbate vascular disease by causing elevation of blood homocysteine in patients who are given this drug for tuberculosis. Isoniazide is known to antagonize the action of vitamin B6, and some side effects of the drug are controlled by vitamin B6 supplements. Years later it was found that many drugs, including isoniazide, elevate blood homocysteine. In addition, the response of medical scientists with an interest in vascular disease and knowledge of amino acid metabolism indicated that they understood the potential benefit of this radically new approach to understanding the underlying cause of arteriosclerosis in the population.
From their questions and comments, it was apparent that doctors and medical scientists who adhered to the traditional cholesterol/fat concept of the cause of vascular disease were dubious about the significance of the new discovery. Since there was no indication of abnormality of cholesterol, lipids or fat metabolism in children with homocystinuria, how could this observation have implications for vascular disease in the general population? At this early stage, there was no public criticism of the new approach by adherents of the cholesterol/fat hypothesis. It seemed prudent for me to await developments in understanding of the connection between homocysteine and the cholesterol approach before discussing these questions in my publications. Besides, my knowledge of the biochemistry and pathophysiology of cholesterol, steroid hormones and fats would enable me to explore and understand the connection to homocysteine in the years to come.
A few medical authorities, both in the cholesterol field and in the homocystinuria field, privately denounced the new homocysteine approach to understanding arteriosclerosis. They perceived that the fundamentally different nature of my new discovery threatened to undermine the conventional view of prevention and treatment of arteriosclerosis.
The vast majority of the medical community, however, totally ignored the new homocysteine theory, either because they had little knowledge of this complicated area of biochemistry and metabolism or because they believed there was too little evidence for the theory in previously published research. They believed that the homocysteine theory was of little general interest because it seemed to be applicable directly only to rare genetic diseases of little consequence to arteriosclerosis as it occurs in the general population.
Implications of the Discovery
Why is the suggestion that elevated homocysteine levels cause arteriosclerosis a radical departure from the conventional concept of this disease? Does this new discovery force the medical community to rethink previously accepted theories about the underlying cause of arteriosclerosis? How does the homocysteine theory alter the strategy of public health experts for preventing arteriosclerosis? What are the implications for treatment of patients with heart attack, stroke, kidney failure or gangrene by the medical profession?
The primary implication is that arteriosclerosis is attributable to abnormal processing of protein in the body because of deficiencies of B vitamins in the diet. The homocysteine theory predicts that populations are at risk of the disease because the methionine of dietary protein is not prevented from forming excess homocysteine. This new theory predicts that a dietary imbalance between too much methionine from protein and a deficiency of vitamins B6, B12 and folic acid is the underlying cause of death and disability from vascular disease.
The homocysteine approach is radically different from the traditional view which relates arteriosclerosis to dietary consumption of excess fats and cholesterol. In the conventional view, the arteries are believed to be damaged by a buildup of cholesterol in the LDL component of plasma coupled with a related lowering of the HDL component. The view of the homocysteine theory is that arteries are damaged by the injurious effect of homocysteine on cells and tissues of arteries, setting in motion the many processes that lead to loss of elasticity, hardening and calcification, narrowing of the lumen and formation of blood clots within arteries. The homocysteine theory considers arteriosclerosis a disease of protein intoxication. The cholesterol/fat approach considers the disease to be caused by intoxication from fats.
If the underlying cause of arteriosclerosis were intoxication from eating too much fat and cholesterol, prevention might be easily achieved simply by decreasing consumption of the offending foods that are rich in these substances. However, if the underlying cause of this disease were intoxication by homocysteine formation from dietary protein because of deficiencies of B vitamins, prevention could only be achieved by consumption of foods that provide a limited quantity of methionine and an abundant supply of vitamin B6, B12 and folic acid. In summary then, the homocysteine theory considers arteriosclerosis a result of dietary imbalance from partial vitamin deficiencies whereas the cholesterol approach incriminates the toxicity of dietary fats.
In a disease as complex as arteriosclerosis, many factors besides diet are known to interact and contribute to its development and progression. Some of these factors are aging, the male gender, postmenopausal status in women, familial predisposition, smoking and other toxins, lack of exercise, high blood pressure and thyroid disease. While some correlations between these factors and LDL and HDL levels have been uncovered, there are many cases of severe or fatal arteriosclerosis in which plasma cholesterol, LDL and HDL are quite normal. 13
Within the past decade medical investigators have begun to study blood homocysteine levels in populations and in selected groups of persons at high risk for arteriosclerosis. The exciting news is that an explosion of studies and an avalanche of new findings have begun to confirm the validity of the homocysteine theory. For the first time, it has become possible to conclude that all of the factors known to be of major importance in arteriosclerosis do in fact affect blood homocysteine levels in the ways predicted by the theory.
The further exciting news is that a young or middle-aged person who is interested in preventing vascular disease can use the homocysteine theory to reduce risk of arteriosclerosis in his or her later years. For the person with early or established vascular disease, the homocysteine approach offers a promising alternative to the traditional approach to medical therapy. Studies are currently under way in many medical centers and clinics to assess the potential benefits of the homocysteine approach to patients with vascular disease.
Finally, recent developments have suggested that damage to the arteries by homocysteine may depend upon the way in which homocysteine is carried by the LDL of plasma. 14 This new understanding has the potential for uniting the extensive field of knowledge about cholesterol and fats with the insights of the homocysteine theory of arteriosclerosis.
In future years the beneficial influence of the homocysteine approach on health and longevity promises to be tremendous. Already the continuing major declines in the risk of stroke and heart attack since the mid 1960s in America have been related to increased vitamin B6 in the food supply. 15 Recent studies have suggested that the addition of folic acid to the food supply could save a minimum of 50,000 American lives each year from heart disease alone. 16 A well-coordinated future effort to supply foods to the population with the proper balance between protein and vitamins B6, B12 and folic acid is anticipated to have a major impact on health and life expectancy. Finally, as explained in succeeding chapters, individuals can now acquire the knowledge necessary to prevent devastating damage to the arteries in later years.
REFERENCES
1. Case Records of the Massachusetts General Hospital, "Case 19471. Marked cerebral symptoms following a limp of three months' duration." New England Journal of Medicine 209: 1063-1066, 1933.
2. Nina A.J. Carson, C.E. Dent, C.M.B. Field and Gerald E. Gaull, "Homocystinuria. Clinical and pathological review of ten cases." Journal of Pediatrics 66:565-583, 1965.
The Homocysteine Revolution
3. R. Neil Schimke, Victor A. McKusick, Thomas Huang and Abou D. Pollack, "Homocystinuria. Studies of 20 families with 38 affected members." Journal of the American Medical Association 193:711-719, 1965.
4. S. Harvey Mudd, Harvey L. Levy and Robert H. Abeles, "A derangement in B12 metabolism leading to homocysti-nemia, cystathioninemia and methylmalonic aciduria." Biochemical and Biophysical Research Communications 35:121-126, 1969.
5. George V. Mann, Stephen B. Andrus, Ann McNally and Fredrick J. Stare, "Experimental atherosclerosis in Cebus monkeys." Journal of Experimental Medicine 98:195-218. 1953.
6. John V. Klavins, "Pathology of amino acid excess. Effects of administration of excessive amounts of sulphur containing amino acids: homocystine." British Journal of Experimental Pathology 44:507-515, 1963.
7. James F. Rinehart and Louis D. Greenberg, "Arteriosclerotic lesions in pyridoxine-deficient monkeys." American Journal of Pathology 25:481-491, 1949.
8. W. Stanley Hartroft, J.H. Ridout, E.A. Sellers and Charles H. Best, "Atheromatous changes in aorta, carotid, and coronary arteries of choline-deficient rats." Proceedings of the Society for Experimental Biology and Medicine 81:384-393, 1952.
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