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Hyperhomocysteinemia in Retinal Artery and Retinal Vein Occlusion
Hyperhomocysteinemia in Retinal Artery and Retinal Vein Occlusion Erwin M. Wenzler, M.D., Adrianus J. J. M. Rademakers, M.D., Godfried H. J. Boers, M.D., [ohan R. M. Cruysberg, M.D., Carroll A. B. Webers, M.D., and August F. Deutman, M.D.
In 19 patients who had retinal vein occlusion or retinal artery occlusion before the age of 50 years, the incidence of hyperhomocysteinemia, as observed in heterozygosity for homocystinuria, was studied by the performance of a standardized, oral methionineloading test. In four of the 19 patients (21%), two with retinal artery occlusion and two with central retinal vein occlusion, the afterload peak levels of homocysteine exceeded the mean level, established in normal control subjects, by more than two standard deviations and were as well within the ranges established in obligate heterozygotes for homocystinuria. Because the frequency of heterozygosity for homocystinuria in the normal population is one in 70 (1.4%) at the most, we conclude that hyperhomocysteinemia predisposes to the development of premature retinal artery and retinal vein occlusion (P < .01; X2 test). is usually associated ophthalmologically with ectopia lentis. Abnormal accumulation of homocysteine in plasma, as found in this inborn error of metabolism of the amino acid methionine, also has a toxic effect on endothelial cells resulting in arteriosclerosis, and arterial and venous thromboembolic events at a young age. These complications are HOMOCYSTINURIA
Accepted for publication Oct. 23, 1992. From the Departments of Ophthalmology (Drs. Wenzler, Rademakers, Cruysberg, Webers, and Deutman) and Internal Medicine (Dr. Boers), University Hospital Nijmegen, Nijmegen, The Netherlands. Reprint requests to Erwin M. Wenzler, M.D., Department of Ophthalmology, University Hospital Nijmegen, P.O. Box 9101, 6500 NB Nijmegen, The Netherlands.
162
well known in internal medicine, neurology, and pediatrics but are seldom seen in ophthalmology. Retinal artery occlusions, without as well as in combination with local predisposing factors have been described in four homozygous patients.!" Mild hyperhomocysteinemia in heterozygosity for homocystinuria also predisposes to the development of occlusive arterial and venous disease, leading to clinical disorders such as cerebrovascular occlusions, coronary artery disease, intermittent claudication, and renovascular abnormalities in young patients."? Abnormally high homocysteinemia levels caused by homozygous homocystinuria can be lowered by treatment with high doses of vitamin B6, folic acid, or betaine, cofactor or substrates in the homocysteine metabolism.v" Such therapy can prevent cerebrovascular accidents, arterial and venous thromboembolic disorders, and coronary artery disease." Also in heterozygotes pathologic hyperhomocysteinemia can be normalized by such treatment.' In 1985 the diagnosis heterozygosity for homocystinuria was documented in our clinic in a patient with retinal artery occlusion. This observation challenged us to explore the possibility that mild hyperhomocysteinemia, as present in carriers, might be a risk factor of premature retinal artery or retinal vein occlusion. Therefore we studied 33 patients, less than 50 years of age at the time of the first retinal vascular occlusion, manifesting one of these disorders between 1985 and 1990. In 20 patients no ocular or systemic cause such as diabetes, hyperlipoproteinemia, hypertension, or glaucoma was present. The incidence of hyperhomocysteinemia was studied in 19 patients of this group by the performance of a standardized, oral methionine-loading test.
©AMERlCAN JOURNAL OF OPHTHALMOLOGY
115:162-167,
FEBRUARY,
1993
Vol. 115, No.2
Hyperhomocysteinemia
Patients and Methods We selected all 33 patients with central retinal artery occlusion, branch retinal artery occlusion, central retinal vein occlusion, and branch retinal vein occlusion. The patients underwent complete ophthalmic examination, complete history taking, and general physical examination by an internist. On the basis of the results of the examinations, laboratory studies and special diagnostic studies were performed. The diagnosis of the ophthalmic disorder was documented by angiography in 30 patients and by ophthalmoscopy in three patients: two normohomocysteinemic patients and one hyperhomocysteinemic patient (Patient 2 in the Table). Thirteen patients (39.4%) with diabetes mellitus (fasting plasma glucose levels of 5.6 mmol Zl or more), hyperlipoproteinemia (fasting serum levels of cholesterol of 6.5 mmol Zl or more and triglycerides of 2.0 mmol /I or more), hypertension (patients who received antihypertensive therapy or had a systolic and diastolic blood pressure in the supine position of more than 150 and 90 mm Hg, respectively, on three measurements), thromboembolic disorders, conditions known to disturb methionine metabolism (such as renal failure and liver cirrhosis), or patients with questionable diagnosis of the ophthalmic disorder were excluded. One patient had a history of diabetes mellitus. One patient had hypercholesterolemia (found on examination after the occlusion). Five patients had a history of hypertension. Two patients had valvular heart disorders (found by cardiac examination after the occlusion). Two patients had undergone renal transplantation in the past, and two patients had questionable diagnosis of the retinal vascular occlusion. Twenty patients (60.6%) were admitted into the study. The group with retinal artery occlusion finally consisted of four patients with branch retinal artery occlusion and one patient with central retinal artery occlusion and branch retinal artery occlusion. The group with retinal vein occlusion consisted of 14 patients with central retinal vein occlusion and one patient with branch retinal vein occlusion. The patient with branch retinal vein occlusion refused to participate in the study. At the time of testing, all patients had normal renal functions (urea, 3.0 to 7.0 mmol /I and creatinine, 60 to 100 mmol /I). and liver functions (aspartate amino-
163
transferase and alanine aminotransferase less than 25 U II). The plasma levels of vitamin B6 (35 to 107 nmol/l), vitamin BI 2 (0.160 to 0.700 nmol Zl), and folic acid (5.5 to 40.0 nmol Zl) were also normal. Details concerning the standardization of the oral methionine-loading and the analytic methods used in the measurement of amino acids by the laboratory of our center were described previously." In summary, after an overnight fast, oral L-methionine was administered at 9:00 A.M. in a loading dose of 0.1 g (0.7 mmol) per kilogram of body weight. During the test the patients used a diet with a methionine content that was restricted to a total of 14 mg. Homocysteine is rapidly oxidized during blood sampling and amino acid analysis with conventional procedures. It is measured only as the disulfides homocystine (homocysteine-S-S-homocysteine) and homocysteine-cysteine mixed disulfide (homocysteine-S-S-cysteine). The total amount of circulating nonprotein-bound homocysteine in a blood sample was calculated as twice the concentration of homocystine plus the concentration of homocysteine-cysteine mixed disulfide (expressed in micromoles per liter). Venous blood samples were obtained at four, six, and eight hours after loading. Methionine, homocystine, and homocysteine-cysteine mixed disulfide were measured in the serum of venous blood samples by ion-exchange chromatography. The limit of detection for both homocystine and homocysteine-cysteine mixed disulfide is 0.1 j.Lmol/l. Values of serum homocysteine were previously determined in normal control subjects and obligate heterozygotes for homocystinuria, according to gender and menopausal status. 11.12 Patients were considered to have hyperhomocysteinemia as seen in obligate heterozygotes for homocystinuria if peak levels of homocysteine measured after methionine-loading exceeded the mean control levels obtained in the respective groups of normal control subjects by more than two standard deviations. In premenopausal women these control levels were 6.8 ± 1.3 j.Lmol/l (mean ± standard deviation); in postmenopausal women levels were 24.1 ± 6.0 umolyl: and in men, 13.3 ± 3.6 j.Lmol/l. Additionally, as criterion for hyperhomocysteinemia the homocysteine levels had to be within the ranges determined in groups of obligate heterozygotes for homocystinuria, which in premenopausal women were 41.0 ±
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24.6 J.Lmol/1 (mean ± standard deviation), in postmenopausal women, 36.6 ± 22.2 umolj'l, and in men, 26.7 ± 12.7 urnol /I. Statistical analysis of the frequency of heterozygosity for homocystinuria was performed with the X2 test.
Results
In four of the 19 patients (21 %) after methionine-loading, the peak levels of homocysteine exceeded the mean level established in normal control subjects by more than two standard deviations and were also within the ranges established in obligate heterozygotes (Table). Therefore, these four patients could be considered as hyperhomocysteinemic. Two of these patients (Patients 1 and 2) belonged to the group with retinal artery occlusions, the other
two patients (Patients 3 and 4) had central retinal vein occlusions. In one of the 19 patients the peak level of homocysteine was within the range established in obligate heterozygote men, but did not exceed the range established in normal control subjects. Therefore, this patient was considered to be normal. In the group with retinal artery occlusions (five patients), two normohomocysteinemic patients with branch retinal artery occlusion had little or no loss of vision after the occlusion. In one of these patients the branch retinal artery occlusion was followed by a nonischemic occlusion of the central retinal vein of the same eye some days later, and visual acuity decreased from 20/25 to 20/100. He was treated with argon laser photocoagulation. Eleven months after the occlusions the visual acuity was 20/ 30. The visual acuity of the third normohornocysteinemic patient with branch retinal artery
TABLE CLINICAL AND LABORATORY FINDINGS IN FOUR PATIENTS WITH HYPERHOMOCYSTEINEMIA PEAK SERUM HOMOCYSTEINE
(llmol/l) PATIENT NO., AGE (YRS).
AFFECTED
GENDER
EYE
1,36, F
RE.
VISUAL ACUITY TYPE OF OCCLUSION
INITIAL'
FINAL
Branch retinal artery occlusion
NA
20/25
L.E.
Central retinal artery occlusion
20/250
20/25
RE.1
Branch retinal artery occlusion
20/40
20/40
L.E.
Branch retinal artery occlusion
20/20
20/20
R.E.1
Branch retinal artery occlusion
20/40
20/40
L.E.
Branch retinal artery occlusion
20/20
20/20
3, 25, F
RE.
Nonischemic central retinal vein occlusion
20/40
20/25
4,37, M
L.E.
Ischemic central retinal vein occlusion
RE.
Nonischemic central retinal vein occlusion
2,22. M
*NA indicates data not available. tDenotes a premenopausal woman. llndicates amblyopia.
Counting fingers
Counting fingers
20/100
20/20
BEFORE
DURING
VITAMIN B,
VITAMIN B,
THERAPY
THERAPY
18.9t
10.1t
47.9
18.7
16.8t
11.8t
32.1
14.7
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Hyperhomocysteinemia
occlusion initially deteriorated to 20/160 and returned to 20/16 within ten days. The two hyperhomocysteinemic patients differed from the other three patients in this group in having recurrent occlusions in both eyes. Patient 1 had a branch retinal artery occlusion in the right eye at the age of 36 years. Four years later she had a central retinal artery occlusion in the left eye. After the second occlusion, visual acuity initially was reduced to 20/250 but returned to 20/25. Patient 2 had branch retinal artery occlusions in both eyes and permanent defects in the corresponding sectorial visual fields at 22 and 24 years of age without loss of vision. Except for the normohomocysteinemic patient with branch retinal artery occlusion followed by a nonischemic central retinal vein occlusion, we did not apply any specific treatment to the patients in this group. In the venous group (14 patients), nonischemic occlusion was seen in 11 eyes (nine normohomocysteinemic patients, Patient 3, and in the right eye of Patient 4) with a visual acuity after the occlusion varying from 20/200 to 20/20 and a recovery varying from 20/80 to 20/20. Permanent impairment of visual acuity in two of the normohomocysteinemic patients was caused by chronic cystoid macular edema. In the group of patients with ischemic central retinal vein occlusion (five patients), severe loss of vision was seen directly after the occlusion in three patients (Patient 4 and two normohomocysteinemic patients). Some months later the other two normohomocysteinemic patients of this group developed neovascular glaucoma. Visual acuity decreased to hand motion in one of the two patients. In the other patient visual acuity deteriorated to no light perception. None of the five patients recovered useful visual acuity. We saw recurrent occlusions of the central retinal vein in two patients of the venous group, one patient with normohomocysteinemia, and one patient with hyperhomocysteinemia (Patient 4). This patient had had an ischemic central retinal vein occlusion at the age of 37 years in the left eye. Three years later he had a nonischemic central retinal vein occlusion in the right eye; visual acuity deteriorated to 20/100 and returned to 20/20 within 12 days. Patient 3, the second hyperhomocysteinemic patient of the venous group, had a nonischemic central retinal vein occlusion at the age of 25 years. Visual acuity was 20/40 after the occlusion and improved to 20/25 within three months. Patients 3 and 4 underwent no specific
165
treatment with regard to their nonischemic central retinal vein occlusions. Argon laser photocoagulation was applied to the three patients with ischemic central retinal vein occlusion as well as to the two patients with nonischemic central retinal vein occlusion and chronic macular edema. The patients with neovascular glaucoma underwent cyclocryotherapy. The four hyperhomocysteinemic patients in our population were treated with vitamin B6 (250 mg daily). Six to seven weeks after the start of the therapy we repeated the methionine-loading test. In all four patients we established normalization of the peak levels of homocysteine (Table). Follow-up examinations of the hyperhomocysteinemic patients, including a methionine-loading test, are performed every 12 months. While on vitamin B6 treatment all patients showed normal plasma levels of homocysteine and there have been no recurrences after a follow-up of one to five years. The group studied consisted of six women and 13 men. One of the two hyperhomocysteinemic men (50%) and five of the 11 normohomocysteinemic men (45.5%) smoked. One of the four normohomocysteinemic women (25%) used oral contraceptives, and one of the four women (25%) smoked and also used oral contraceptives. In the hyperhomocysteinemic group one of the two women (50%) smoked and also used oral contraceptives. Signs of other arteriosclerotic disorders, for example occlusive peripheral arterial disease or occlusive cerebrovascular disease, were not observed in any of the 19 patients. In one normohomocysteinemic patient we found a family history of retinal vascular occlusion and glaucoma. Several relatives of Patient 2 had thrombosis of the leg. Two normohomocysteinemic patients had a family history of cerebrovascular disease. Myocardial infarcts appeared in the families of eight normohomocysteinemic patients. Only one of the patients (Patient 2) with a striking family history had hyperhomocysteinemia. At the time of the first occlusion, the age of the patients admitted to the methionine-loading test varied from 22 to 49 years (38.3 ± 9.1 years [mean ± standard deviation)). The mean age in hyperhomocysteinemic patients was lower than in normohomocysteinemic patients. We found 30.0 ± 7.6 years (mean ± standard deviation) and 40.5 ± 8.3 years, respectively. The average age of patients not admitted to the methionine-loading test was 39.9 years (stan-
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AMERICAN JOURNAL OF OPHTHALMOLOGY
dard deviation ± 8.2 years), with a range from 19 to 49 years. All 33 patients were white.
Discussion
Published reports on heterozygosity for homocystinuria show that arterial as well as venous vessels are involved in this disease.t" Therefore we selected a population consisting of patients with a retinal artery occlusion and patients with a retinal vein occlusion. In this population of 19 patients we detected four patients with pathologic peak levels of homocysteine after methionine-loading. Methionine-loading must be considered as the most valid test to detect heterozygosity for homocystinuria, identifying 90% of obligate carriers for this condition." Measurement of low activity of cystathionine synthase in cultured fibroblasts could detect 85% of such obligate carriers." In the majority of prematurely arteriosclerotic patients, in whom hyperhomocysteinemia has been diagnosed by means of a methionine-loading test, low activity of cystathionine synthase, which identifies them as heterozygotes, could be demonstrated.v' Be cause of the absence of factors known to disturb methionine metabolism, such as renal or liver insufficiency or deficiencies of vitamin B6, vitamin BIZ' or folic acid, it is most likely that in these four hyperhomocysteinemic patients with retinal artery occlusion or central retinal vein occlusion heterozygosity for cystathionine synthase deficiency is the cause of their abnormal blood level of homocysteine. The frequency of heterozygosity for homocystinuria in the normal population has been estimated to be one in 70 (1.4%) at the most." We detected four hyperhomocysteinemic individuals among 19 patients (21 %, exact 95% confidence interval: 6% to 46%,13 Similar frequencies of hyperhomocysteinemia caused by heterozygosity for homocystinuria are detected in patients with peripheral or cerebrovascular arteriosclerosis.v' Therefore, in our opinion the high frequency of hyperhomocysteinemia found in this group of patients is evidence of an increased risk to develop premature retinal vascular occlusion (P < .01; X2 test). The group of patients with retinal vascular disorders at a young age is small. To achieve confirmation of the finding in the study screening for hyperho-
mocysteinemia in such patients is ongoing in our clinic. In The Netherlands most persons are smokers, and most younger women are users of oral contraceptives. For this practical reason we did not exclude these individuals in our previous and ongoing studies of hyperhomocysteinemia. Although the groups are too small to perform statistical analysis, the distribution of patients with or without these risk factors among the hyperhomocysteinemic and normohomocysteinemic groups is virtually equal. With regard to the course of the disease the findings in our patients were similar to that in other studies.":" Furthermore the visual prognosis in the hyperhomocysteinemic patients appears to be similar to that in the normohomocysteinemic patients. It is of interest to note the patients with recurrent occlusions. Only one in 15 normohomocysteinemic patients had recurrent occlusions; however, in two of the four hyperhomocysteinemic patients (Patients 1 and 4) there was a recurrence in the period before the start of treatment with vitamin B6, in one more hyperhomocysteinemic patient (Patient 2) a second recurrence occurred two weeks after starting treatment. By repeating a methionineloading test seven weeks after the start of therapy with vitamin B6, we established a normal peak level of homocysteine. Probably, at the moment of the recurrence this patient had not yet a normal blood level of homocysteine. We are currently studying the clinical effect of homocysteine-lowering therapy in hyperhomocysteinemic patients with occlusive arterial and venous disease. If a beneficial effect is found in the near future, it seems of practical interest to screen patients with retinal arterial or venous occlusion for hyperhomocysteinemia at a relatively young age. References 1. Berg, W. van de Verbraak, F. D., and Bos, P. J. M.: Homocystinuria presenting as central retinal artery occlusion and longstanding thromboembolic disease. Br. J. Ophthalmol. 74:696, 1990. 2. Mukuno, K., Matsui, K., and Haraguchi, H.: Ocular manifestations of homocystinuria, report of two cases. Acta Soc. Ophthalmol. Jpn. 71:66, 1967. 3. Grobe, H.: Homocystinuria (cystathionine synthase deficiency). Results of treatment in late-diagnosed patients. Eur. J- Pediatr. 135:199, 1980.
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Hyperhomocysteinemia
4. Wilson, R. S., and Ruiz, R. S.: Bilateral central retinal artery occlusion in homocystinuria. Arch. Ophthalmol. 82:267, 1969. 5. Boers, G. H. r, Smals. A. G. H., Trijbels, F. J. M., Fowler, B., Bakkeren, J. A. ]. M., Schoonderwaldt, H. c., Kleijer, W. ]., and Kloppenborg, P. W. c.: Heterozygosity for homocystinuria in premature peripheral and cerebral occlusive arterial disease. N. Engl. J. Med. 313:709, 1985. 6. Brattstrom, 1.: Homocysteine in Vascular Disease. Lund, Sweden, University of Lund, 1989, p. 35. Thesis. 7. Clarke, R., Daly, 1., Robinson, K., Naughten, E., Cahalane, S., Fowler, B., and Graham, I.: Hyperhomocysteinemia. An independent risk factor for vascular disease. N. Engl.]. Med. 324:1149, 1991. 8. Mudd, S. H., Levy, H. 1., and Skovby, F.: Disorders of transsulfuration. In Scriver, C. R., Beaudet, A. 1., Sly, W. S., and Valle, D. (eds.): The Metabolic Basis of Inherited Disease. New York, McGraw-Hill, 1989, pp. 693-734. 9. Boers, G. H. ].: Homocystinuria. A risk factor of premature vascular disease. Clinical Research Series 3. Dordrecht, The Netherlands, Foris Publications, 1986, pp. 41-102. 10. Mudd, S. H., Skovby, F., Levy, H. 1., Pettigrew, K. D., Wilcken, B., Pyeritz, R. E., Andria, G., Boers, G. H. j.. Bromberg, I. 1., Cerone, R., Fowler, B., Grobe, H., Schmidt, H., and Schweitzer, 1.: The
167
natural history of homocystinuria due to cystathionine beta-synthase deficiency. Am. ]. Hum. Genet. 37:1,1985. 11. Boers, G. H. r.. Smals, A. G., Trijbels, F. i. Leerrnakers, A. I., and Kloppenborg, P. W. c.. Unique efficiency of methionine metabolism in premenopausal women may protect against vascular disease in the reproductive years. [, Clin. Invest. 72:1971,1983. 12. Boers, G. H. J., Fowler, B., Smals, A. G. H., TrijbeIs, F. H. M., Leermakers, A. I., Kleijer, W. j.. and Kloppenborg, P. W. c.: Improved identification of heterozygotes for homocystinuria due to cystathionine synthase deficiency by the combination of methionine loading and enzyme determination in cultured fibroblasts. Hum. Genet. 69:164, 1985. 13. Lentner, C.(ed.): Geigy Scientific Tables, vol. 2. Basle, Switzerland, Ciba Geigy Ltd., 1982, p. 89. 14. Karjalainen, K.: Occlusion of the central retinal artery and retinal branch arterioles. A clinical, tonographic and fluorescein angiographic study of 175 patients. Acta Ophthalmol. 109(suppl.): 1, 1971. 15. Brown, G. c.. Magargal, 1. E., Shields, ]. A., Goldberg, R. E., and Walsh, P. N.: Retinal arterial obstruction in children and young adults. Ophthalmology 88:18,1981. 16. Zegarra, H., Gutman, F. A., and Conforto, ].: The natural course of central retinal vein occlusion. Ophthalmology 86:1931,1979.
In 19 patients who had retinal vein occlusion or retinal artery occlusion before the age of 50 years, the incidence of hyperhomocysteinemia, as observed in heterozygosity for homocystinuria, was studied by the performance of a standardized, oral methionineloading test. In four of the 19 patients (21%), two with retinal artery occlusion and two with central retinal vein occlusion, the afterload peak levels of homocysteine exceeded the mean level, established in normal control subjects, by more than two standard deviations and were as well within the ranges established in obligate heterozygotes for homocystinuria. Because the frequency of heterozygosity for homocystinuria in the normal population is one in 70 (1.4%) at the most, we conclude that hyperhomocysteinemia predisposes to the development of premature retinal artery and retinal vein occlusion (P < .01; X2 test). is usually associated ophthalmologically with ectopia lentis. Abnormal accumulation of homocysteine in plasma, as found in this inborn error of metabolism of the amino acid methionine, also has a toxic effect on endothelial cells resulting in arteriosclerosis, and arterial and venous thromboembolic events at a young age. These complications are HOMOCYSTINURIA
Accepted for publication Oct. 23, 1992. From the Departments of Ophthalmology (Drs. Wenzler, Rademakers, Cruysberg, Webers, and Deutman) and Internal Medicine (Dr. Boers), University Hospital Nijmegen, Nijmegen, The Netherlands. Reprint requests to Erwin M. Wenzler, M.D., Department of Ophthalmology, University Hospital Nijmegen, P.O. Box 9101, 6500 NB Nijmegen, The Netherlands.
162
well known in internal medicine, neurology, and pediatrics but are seldom seen in ophthalmology. Retinal artery occlusions, without as well as in combination with local predisposing factors have been described in four homozygous patients.!" Mild hyperhomocysteinemia in heterozygosity for homocystinuria also predisposes to the development of occlusive arterial and venous disease, leading to clinical disorders such as cerebrovascular occlusions, coronary artery disease, intermittent claudication, and renovascular abnormalities in young patients."? Abnormally high homocysteinemia levels caused by homozygous homocystinuria can be lowered by treatment with high doses of vitamin B6, folic acid, or betaine, cofactor or substrates in the homocysteine metabolism.v" Such therapy can prevent cerebrovascular accidents, arterial and venous thromboembolic disorders, and coronary artery disease." Also in heterozygotes pathologic hyperhomocysteinemia can be normalized by such treatment.' In 1985 the diagnosis heterozygosity for homocystinuria was documented in our clinic in a patient with retinal artery occlusion. This observation challenged us to explore the possibility that mild hyperhomocysteinemia, as present in carriers, might be a risk factor of premature retinal artery or retinal vein occlusion. Therefore we studied 33 patients, less than 50 years of age at the time of the first retinal vascular occlusion, manifesting one of these disorders between 1985 and 1990. In 20 patients no ocular or systemic cause such as diabetes, hyperlipoproteinemia, hypertension, or glaucoma was present. The incidence of hyperhomocysteinemia was studied in 19 patients of this group by the performance of a standardized, oral methionine-loading test.
©AMERlCAN JOURNAL OF OPHTHALMOLOGY
115:162-167,
FEBRUARY,
1993
Vol. 115, No.2
Hyperhomocysteinemia
Patients and Methods We selected all 33 patients with central retinal artery occlusion, branch retinal artery occlusion, central retinal vein occlusion, and branch retinal vein occlusion. The patients underwent complete ophthalmic examination, complete history taking, and general physical examination by an internist. On the basis of the results of the examinations, laboratory studies and special diagnostic studies were performed. The diagnosis of the ophthalmic disorder was documented by angiography in 30 patients and by ophthalmoscopy in three patients: two normohomocysteinemic patients and one hyperhomocysteinemic patient (Patient 2 in the Table). Thirteen patients (39.4%) with diabetes mellitus (fasting plasma glucose levels of 5.6 mmol Zl or more), hyperlipoproteinemia (fasting serum levels of cholesterol of 6.5 mmol Zl or more and triglycerides of 2.0 mmol /I or more), hypertension (patients who received antihypertensive therapy or had a systolic and diastolic blood pressure in the supine position of more than 150 and 90 mm Hg, respectively, on three measurements), thromboembolic disorders, conditions known to disturb methionine metabolism (such as renal failure and liver cirrhosis), or patients with questionable diagnosis of the ophthalmic disorder were excluded. One patient had a history of diabetes mellitus. One patient had hypercholesterolemia (found on examination after the occlusion). Five patients had a history of hypertension. Two patients had valvular heart disorders (found by cardiac examination after the occlusion). Two patients had undergone renal transplantation in the past, and two patients had questionable diagnosis of the retinal vascular occlusion. Twenty patients (60.6%) were admitted into the study. The group with retinal artery occlusion finally consisted of four patients with branch retinal artery occlusion and one patient with central retinal artery occlusion and branch retinal artery occlusion. The group with retinal vein occlusion consisted of 14 patients with central retinal vein occlusion and one patient with branch retinal vein occlusion. The patient with branch retinal vein occlusion refused to participate in the study. At the time of testing, all patients had normal renal functions (urea, 3.0 to 7.0 mmol /I and creatinine, 60 to 100 mmol /I). and liver functions (aspartate amino-
163
transferase and alanine aminotransferase less than 25 U II). The plasma levels of vitamin B6 (35 to 107 nmol/l), vitamin BI 2 (0.160 to 0.700 nmol Zl), and folic acid (5.5 to 40.0 nmol Zl) were also normal. Details concerning the standardization of the oral methionine-loading and the analytic methods used in the measurement of amino acids by the laboratory of our center were described previously." In summary, after an overnight fast, oral L-methionine was administered at 9:00 A.M. in a loading dose of 0.1 g (0.7 mmol) per kilogram of body weight. During the test the patients used a diet with a methionine content that was restricted to a total of 14 mg. Homocysteine is rapidly oxidized during blood sampling and amino acid analysis with conventional procedures. It is measured only as the disulfides homocystine (homocysteine-S-S-homocysteine) and homocysteine-cysteine mixed disulfide (homocysteine-S-S-cysteine). The total amount of circulating nonprotein-bound homocysteine in a blood sample was calculated as twice the concentration of homocystine plus the concentration of homocysteine-cysteine mixed disulfide (expressed in micromoles per liter). Venous blood samples were obtained at four, six, and eight hours after loading. Methionine, homocystine, and homocysteine-cysteine mixed disulfide were measured in the serum of venous blood samples by ion-exchange chromatography. The limit of detection for both homocystine and homocysteine-cysteine mixed disulfide is 0.1 j.Lmol/l. Values of serum homocysteine were previously determined in normal control subjects and obligate heterozygotes for homocystinuria, according to gender and menopausal status. 11.12 Patients were considered to have hyperhomocysteinemia as seen in obligate heterozygotes for homocystinuria if peak levels of homocysteine measured after methionine-loading exceeded the mean control levels obtained in the respective groups of normal control subjects by more than two standard deviations. In premenopausal women these control levels were 6.8 ± 1.3 j.Lmol/l (mean ± standard deviation); in postmenopausal women levels were 24.1 ± 6.0 umolyl: and in men, 13.3 ± 3.6 j.Lmol/l. Additionally, as criterion for hyperhomocysteinemia the homocysteine levels had to be within the ranges determined in groups of obligate heterozygotes for homocystinuria, which in premenopausal women were 41.0 ±
164
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AMERICAN JOURNAL OF OPHTHALMOLOGY
24.6 J.Lmol/1 (mean ± standard deviation), in postmenopausal women, 36.6 ± 22.2 umolj'l, and in men, 26.7 ± 12.7 urnol /I. Statistical analysis of the frequency of heterozygosity for homocystinuria was performed with the X2 test.
Results
In four of the 19 patients (21 %) after methionine-loading, the peak levels of homocysteine exceeded the mean level established in normal control subjects by more than two standard deviations and were also within the ranges established in obligate heterozygotes (Table). Therefore, these four patients could be considered as hyperhomocysteinemic. Two of these patients (Patients 1 and 2) belonged to the group with retinal artery occlusions, the other
two patients (Patients 3 and 4) had central retinal vein occlusions. In one of the 19 patients the peak level of homocysteine was within the range established in obligate heterozygote men, but did not exceed the range established in normal control subjects. Therefore, this patient was considered to be normal. In the group with retinal artery occlusions (five patients), two normohomocysteinemic patients with branch retinal artery occlusion had little or no loss of vision after the occlusion. In one of these patients the branch retinal artery occlusion was followed by a nonischemic occlusion of the central retinal vein of the same eye some days later, and visual acuity decreased from 20/25 to 20/100. He was treated with argon laser photocoagulation. Eleven months after the occlusions the visual acuity was 20/ 30. The visual acuity of the third normohornocysteinemic patient with branch retinal artery
TABLE CLINICAL AND LABORATORY FINDINGS IN FOUR PATIENTS WITH HYPERHOMOCYSTEINEMIA PEAK SERUM HOMOCYSTEINE
(llmol/l) PATIENT NO., AGE (YRS).
AFFECTED
GENDER
EYE
1,36, F
RE.
VISUAL ACUITY TYPE OF OCCLUSION
INITIAL'
FINAL
Branch retinal artery occlusion
NA
20/25
L.E.
Central retinal artery occlusion
20/250
20/25
RE.1
Branch retinal artery occlusion
20/40
20/40
L.E.
Branch retinal artery occlusion
20/20
20/20
R.E.1
Branch retinal artery occlusion
20/40
20/40
L.E.
Branch retinal artery occlusion
20/20
20/20
3, 25, F
RE.
Nonischemic central retinal vein occlusion
20/40
20/25
4,37, M
L.E.
Ischemic central retinal vein occlusion
RE.
Nonischemic central retinal vein occlusion
2,22. M
*NA indicates data not available. tDenotes a premenopausal woman. llndicates amblyopia.
Counting fingers
Counting fingers
20/100
20/20
BEFORE
DURING
VITAMIN B,
VITAMIN B,
THERAPY
THERAPY
18.9t
10.1t
47.9
18.7
16.8t
11.8t
32.1
14.7
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occlusion initially deteriorated to 20/160 and returned to 20/16 within ten days. The two hyperhomocysteinemic patients differed from the other three patients in this group in having recurrent occlusions in both eyes. Patient 1 had a branch retinal artery occlusion in the right eye at the age of 36 years. Four years later she had a central retinal artery occlusion in the left eye. After the second occlusion, visual acuity initially was reduced to 20/250 but returned to 20/25. Patient 2 had branch retinal artery occlusions in both eyes and permanent defects in the corresponding sectorial visual fields at 22 and 24 years of age without loss of vision. Except for the normohomocysteinemic patient with branch retinal artery occlusion followed by a nonischemic central retinal vein occlusion, we did not apply any specific treatment to the patients in this group. In the venous group (14 patients), nonischemic occlusion was seen in 11 eyes (nine normohomocysteinemic patients, Patient 3, and in the right eye of Patient 4) with a visual acuity after the occlusion varying from 20/200 to 20/20 and a recovery varying from 20/80 to 20/20. Permanent impairment of visual acuity in two of the normohomocysteinemic patients was caused by chronic cystoid macular edema. In the group of patients with ischemic central retinal vein occlusion (five patients), severe loss of vision was seen directly after the occlusion in three patients (Patient 4 and two normohomocysteinemic patients). Some months later the other two normohomocysteinemic patients of this group developed neovascular glaucoma. Visual acuity decreased to hand motion in one of the two patients. In the other patient visual acuity deteriorated to no light perception. None of the five patients recovered useful visual acuity. We saw recurrent occlusions of the central retinal vein in two patients of the venous group, one patient with normohomocysteinemia, and one patient with hyperhomocysteinemia (Patient 4). This patient had had an ischemic central retinal vein occlusion at the age of 37 years in the left eye. Three years later he had a nonischemic central retinal vein occlusion in the right eye; visual acuity deteriorated to 20/100 and returned to 20/20 within 12 days. Patient 3, the second hyperhomocysteinemic patient of the venous group, had a nonischemic central retinal vein occlusion at the age of 25 years. Visual acuity was 20/40 after the occlusion and improved to 20/25 within three months. Patients 3 and 4 underwent no specific
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treatment with regard to their nonischemic central retinal vein occlusions. Argon laser photocoagulation was applied to the three patients with ischemic central retinal vein occlusion as well as to the two patients with nonischemic central retinal vein occlusion and chronic macular edema. The patients with neovascular glaucoma underwent cyclocryotherapy. The four hyperhomocysteinemic patients in our population were treated with vitamin B6 (250 mg daily). Six to seven weeks after the start of the therapy we repeated the methionine-loading test. In all four patients we established normalization of the peak levels of homocysteine (Table). Follow-up examinations of the hyperhomocysteinemic patients, including a methionine-loading test, are performed every 12 months. While on vitamin B6 treatment all patients showed normal plasma levels of homocysteine and there have been no recurrences after a follow-up of one to five years. The group studied consisted of six women and 13 men. One of the two hyperhomocysteinemic men (50%) and five of the 11 normohomocysteinemic men (45.5%) smoked. One of the four normohomocysteinemic women (25%) used oral contraceptives, and one of the four women (25%) smoked and also used oral contraceptives. In the hyperhomocysteinemic group one of the two women (50%) smoked and also used oral contraceptives. Signs of other arteriosclerotic disorders, for example occlusive peripheral arterial disease or occlusive cerebrovascular disease, were not observed in any of the 19 patients. In one normohomocysteinemic patient we found a family history of retinal vascular occlusion and glaucoma. Several relatives of Patient 2 had thrombosis of the leg. Two normohomocysteinemic patients had a family history of cerebrovascular disease. Myocardial infarcts appeared in the families of eight normohomocysteinemic patients. Only one of the patients (Patient 2) with a striking family history had hyperhomocysteinemia. At the time of the first occlusion, the age of the patients admitted to the methionine-loading test varied from 22 to 49 years (38.3 ± 9.1 years [mean ± standard deviation)). The mean age in hyperhomocysteinemic patients was lower than in normohomocysteinemic patients. We found 30.0 ± 7.6 years (mean ± standard deviation) and 40.5 ± 8.3 years, respectively. The average age of patients not admitted to the methionine-loading test was 39.9 years (stan-
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dard deviation ± 8.2 years), with a range from 19 to 49 years. All 33 patients were white.
Discussion
Published reports on heterozygosity for homocystinuria show that arterial as well as venous vessels are involved in this disease.t" Therefore we selected a population consisting of patients with a retinal artery occlusion and patients with a retinal vein occlusion. In this population of 19 patients we detected four patients with pathologic peak levels of homocysteine after methionine-loading. Methionine-loading must be considered as the most valid test to detect heterozygosity for homocystinuria, identifying 90% of obligate carriers for this condition." Measurement of low activity of cystathionine synthase in cultured fibroblasts could detect 85% of such obligate carriers." In the majority of prematurely arteriosclerotic patients, in whom hyperhomocysteinemia has been diagnosed by means of a methionine-loading test, low activity of cystathionine synthase, which identifies them as heterozygotes, could be demonstrated.v' Be cause of the absence of factors known to disturb methionine metabolism, such as renal or liver insufficiency or deficiencies of vitamin B6, vitamin BIZ' or folic acid, it is most likely that in these four hyperhomocysteinemic patients with retinal artery occlusion or central retinal vein occlusion heterozygosity for cystathionine synthase deficiency is the cause of their abnormal blood level of homocysteine. The frequency of heterozygosity for homocystinuria in the normal population has been estimated to be one in 70 (1.4%) at the most." We detected four hyperhomocysteinemic individuals among 19 patients (21 %, exact 95% confidence interval: 6% to 46%,13 Similar frequencies of hyperhomocysteinemia caused by heterozygosity for homocystinuria are detected in patients with peripheral or cerebrovascular arteriosclerosis.v' Therefore, in our opinion the high frequency of hyperhomocysteinemia found in this group of patients is evidence of an increased risk to develop premature retinal vascular occlusion (P < .01; X2 test). The group of patients with retinal vascular disorders at a young age is small. To achieve confirmation of the finding in the study screening for hyperho-
mocysteinemia in such patients is ongoing in our clinic. In The Netherlands most persons are smokers, and most younger women are users of oral contraceptives. For this practical reason we did not exclude these individuals in our previous and ongoing studies of hyperhomocysteinemia. Although the groups are too small to perform statistical analysis, the distribution of patients with or without these risk factors among the hyperhomocysteinemic and normohomocysteinemic groups is virtually equal. With regard to the course of the disease the findings in our patients were similar to that in other studies.":" Furthermore the visual prognosis in the hyperhomocysteinemic patients appears to be similar to that in the normohomocysteinemic patients. It is of interest to note the patients with recurrent occlusions. Only one in 15 normohomocysteinemic patients had recurrent occlusions; however, in two of the four hyperhomocysteinemic patients (Patients 1 and 4) there was a recurrence in the period before the start of treatment with vitamin B6, in one more hyperhomocysteinemic patient (Patient 2) a second recurrence occurred two weeks after starting treatment. By repeating a methionineloading test seven weeks after the start of therapy with vitamin B6, we established a normal peak level of homocysteine. Probably, at the moment of the recurrence this patient had not yet a normal blood level of homocysteine. We are currently studying the clinical effect of homocysteine-lowering therapy in hyperhomocysteinemic patients with occlusive arterial and venous disease. If a beneficial effect is found in the near future, it seems of practical interest to screen patients with retinal arterial or venous occlusion for hyperhomocysteinemia at a relatively young age. References 1. Berg, W. van de Verbraak, F. D., and Bos, P. J. M.: Homocystinuria presenting as central retinal artery occlusion and longstanding thromboembolic disease. Br. J. Ophthalmol. 74:696, 1990. 2. Mukuno, K., Matsui, K., and Haraguchi, H.: Ocular manifestations of homocystinuria, report of two cases. Acta Soc. Ophthalmol. Jpn. 71:66, 1967. 3. Grobe, H.: Homocystinuria (cystathionine synthase deficiency). Results of treatment in late-diagnosed patients. Eur. J- Pediatr. 135:199, 1980.
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4. Wilson, R. S., and Ruiz, R. S.: Bilateral central retinal artery occlusion in homocystinuria. Arch. Ophthalmol. 82:267, 1969. 5. Boers, G. H. r, Smals. A. G. H., Trijbels, F. J. M., Fowler, B., Bakkeren, J. A. ]. M., Schoonderwaldt, H. c., Kleijer, W. ]., and Kloppenborg, P. W. c.: Heterozygosity for homocystinuria in premature peripheral and cerebral occlusive arterial disease. N. Engl. J. Med. 313:709, 1985. 6. Brattstrom, 1.: Homocysteine in Vascular Disease. Lund, Sweden, University of Lund, 1989, p. 35. Thesis. 7. Clarke, R., Daly, 1., Robinson, K., Naughten, E., Cahalane, S., Fowler, B., and Graham, I.: Hyperhomocysteinemia. An independent risk factor for vascular disease. N. Engl.]. Med. 324:1149, 1991. 8. Mudd, S. H., Levy, H. 1., and Skovby, F.: Disorders of transsulfuration. In Scriver, C. R., Beaudet, A. 1., Sly, W. S., and Valle, D. (eds.): The Metabolic Basis of Inherited Disease. New York, McGraw-Hill, 1989, pp. 693-734. 9. Boers, G. H. ].: Homocystinuria. A risk factor of premature vascular disease. Clinical Research Series 3. Dordrecht, The Netherlands, Foris Publications, 1986, pp. 41-102. 10. Mudd, S. H., Skovby, F., Levy, H. 1., Pettigrew, K. D., Wilcken, B., Pyeritz, R. E., Andria, G., Boers, G. H. j.. Bromberg, I. 1., Cerone, R., Fowler, B., Grobe, H., Schmidt, H., and Schweitzer, 1.: The
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natural history of homocystinuria due to cystathionine beta-synthase deficiency. Am. ]. Hum. Genet. 37:1,1985. 11. Boers, G. H. r.. Smals, A. G., Trijbels, F. i. Leerrnakers, A. I., and Kloppenborg, P. W. c.. Unique efficiency of methionine metabolism in premenopausal women may protect against vascular disease in the reproductive years. [, Clin. Invest. 72:1971,1983. 12. Boers, G. H. J., Fowler, B., Smals, A. G. H., TrijbeIs, F. H. M., Leermakers, A. I., Kleijer, W. j.. and Kloppenborg, P. W. c.: Improved identification of heterozygotes for homocystinuria due to cystathionine synthase deficiency by the combination of methionine loading and enzyme determination in cultured fibroblasts. Hum. Genet. 69:164, 1985. 13. Lentner, C.(ed.): Geigy Scientific Tables, vol. 2. Basle, Switzerland, Ciba Geigy Ltd., 1982, p. 89. 14. Karjalainen, K.: Occlusion of the central retinal artery and retinal branch arterioles. A clinical, tonographic and fluorescein angiographic study of 175 patients. Acta Ophthalmol. 109(suppl.): 1, 1971. 15. Brown, G. c.. Magargal, 1. E., Shields, ]. A., Goldberg, R. E., and Walsh, P. N.: Retinal arterial obstruction in children and young adults. Ophthalmology 88:18,1981. 16. Zegarra, H., Gutman, F. A., and Conforto, ].: The natural course of central retinal vein occlusion. Ophthalmology 86:1931,1979.