No association of an insertion/deletion polymorphism in the angiotensin I converting enzyme gene with bipolar or unipolar affective disorders
Abstract
A recent Japanese study on the angiotensin I converting enzyme gene (ACE) insertion/deletion polymorphism reported that both the D allele (P < 0.02) and the DD genotype (P < 0.002) were significantly more frequent in affective disorder cases than in controls [Arinami et al., 1996: Biol Psychiatry 40:1122–1127]. A replication study was performed by using 157 bipolar I affective disorder cases, 169 major depressive disorder cases, and 313 controls. No significant association with this polymorphism was found in either disorder or in a combined affective disorder group. These results do not support the ACE gene having a major role in the etiology of either bipolar or unipolar affective disorders. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:733–735, 2000. © 2000 Wiley-Liss, Inc.
INTRODUCTION
Twin, family, and adoption studies provide strong support for genetic factors in the pathogenesis of bipolar affective disorder (manic depression) and unipolar affective disorder. However, there may be some factors that are common to both disorders, because first-degree relatives of bipolar probands seem to have increased risks for both bipolar and unipolar affective disorders [McGuffin and Katz, 1989; Gershon, 1990].
The angiotensin I converting enzyme (ACE) catalyzes the conversion of angiotensin I to the active form, angiotensin II. Levels of serum and peripheral cellular ACE are controlled by a strong genetic component [Cambien et al., 1988]. An insertion/deletion (I/D) polymorphism in intron 16 of the ACE gene is associated with variability in serum ACE levels [Rigat et al., 1990; Tiret et al., 1992]. The ACE gene was considered as a candidate for affective disorder for several reasons. First, ACE can degrade substance P, a potential neuropeptide transmitter. Substance P-like activity, measured by radioimmunoassay, was reported to be significantly higher in the CSF of patients with depressive disorder compared with controls [Rimon et al., 1984], although Berrettini et al. [1985] did not replicate the results of this study. Second, ACE levels were higher in the substantia nigra of a suicide group compared with nonsuicide group [Arregui et al., 1980], and ACE inhibitors have been anecdotally associated with mood-elevating properties [Zubenko and Nixon, 1984]. Third, Arinami et al. [1996] analyzed the ACE I/D polymorphism in 31 bipolar cases and 34 patients with major depression and found that both the D allele (P < 0.02) and the DD genotype (P < 0.002) were significantly more frequent in affective disorder cases than in controls. In this study we aimed to replicate these results by using a larger sample of cases.
MATERIALS AND METHODS
Patients
One hundred fifty-seven (66 male and 91 female) bipolar patients, 169 (58 male and 111 female) unipolar patients, and 313 (132 male and 181 female) controls were typed for the ACE insertion/deletion polymorphism. Control DNA comprising anonymous unrelated individuals from an East Anglian population was obtained from the Molecular Genetics Laboratory, Addenbrooke's Hospital DNA bank. Referral patterns to this laboratory suggest that at least 97% of controls are white, about 80% have parents who were East Anglian, and virtually all of the remainder are from the United Kingdom. The surnames of the controls were screened to exclude individuals who were obviously of nonwhite origin. This region of the United Kingdom includes a large rural catchment area and does not have the ethnic variation seen in many large cities. Ethical approval for genetic studies of bipolar and unipolar affective disorder was obtained from local ethics committees. The bipolar and unipolar patients were recruited from inpatient and outpatient clinics in East Anglia and were English white in origin: both parents were English. The patients were assessed by trained clinicians using the SADS-L interview [Endicott and Spitzer, 1978] supplemented by case note review, meeting research diagnostic criteria for bipolar affective disorder I or major depressive disorder [Spitzer et al., 1978]. The inclusion criteria for the unipolar sample comprised an age of onset of the first episode of depression between the ages of 18 and 65; at least two episodes of unipolar major depression; and at least one in-patient admission for the treatment of depression.
Polymerase Chain Reaction (PCR)
The insertion/deletion polymorphism in intron 16 of the ACE gene [Rigat et al., 1990] was analyzed by PCR as described by Evans et al. [1994]. The genotype frequencies of the ACE polymorphism in the control group did not differ significantly from those expected from the allele frequencies (Table I), on the basis of Hardy-Weinberg equilibrium assumptions (χ2 = 0.018, 2 df, P = 0.99). For the control group, power calculations [Breslow and Day, 1980] show that for a 5% significance level and 80% power, a gene with a relative risk of approximately 2.0 should be detected with alleles with a frequency of 0.526 and 0.474 (Table I).
| Bipolar | Unipolar | Bipolar + Unipolar | Control | |
|---|---|---|---|---|
| Alleles | ||||
| D (%) | 175 (55.7) | 165 (48.8) | 340 (52.1) | 329 (52.6) |
| I (%) | 139 (44.3) | 173 (51.2) | 312 (47.9) | 297 (47.4) |
| Total | 314 | 338 | 652 | 626 |
| Genotypes | ||||
| DD (%) | 49 (31.2) | 40 (23.7) | 89 (27.3) | 88 (28.1) |
| DI (%) | 77 (49.0) | 85 (50.3) | 162 (49.7) | 153 (48.9) |
| II (%) | 31 (19.7) | 44 (26.0) | 75 (23.0) | 72 (23.0) |
| Total | 157 | 169 | 326 | 313 |
| Bipolar vs. control | ||||
| Alleles | χ2 = 0.849, 1 df, P = 0.36 | |||
| Genotypes | χ2 = 0.851, 2 df, P = 0.65 | |||
| Unipolar vs. control | ||||
| Alleles | χ2 = 1.228, 1 df, P = 0.27 | |||
| Genotypes | χ2 = 1.281, 2 df, P = 0.53 | |||
| Bipolar + unipolar vs. control | ||||
| Alleles | χ2 = 0.021, 1 df, P = 0.88 | |||
| Genotypes | χ2 = 0.060, 2 df, P = 0.97 | |||
| Odds ratios (95% CI) | ||||
| Bipolar | ||||
| Alleles I vs. D | 0.88 (0.67–1.15) | |||
| Genotypes II vs. DD | 0.77 (0.45–1.34) | |||
| Genotypes DI vs. DD | 0.90 (0.58–1.40) | |||
| Unipolar | ||||
| Alleles I vs. D | 1.16 (0.89–1.51) | |||
| Genotypes II vs. DD | 1.34 (0.79–2.29) | |||
| Genotypes DI vs. DD | 1.22 (0.77–1.93) | |||
| Bipolar + unipolar | ||||
| Alleles I vs. D | 1.02 (0.82–1.27) | |||
| Genotypes II vs DD | 1.03 (0.66–1.60) | |||
| Genotypes DI vs DD | 1.05 (0.73–1.51) | |||
Statistical Analysis
Odds ratios with 95% confidence intervals were performed by using the general log linear analysis option of the SPSS v6.1 software package (SPSS Inc., Chicago).
RESULTS
Allele and genotype frequencies of the I/D ACE gene polymorphism from both the bipolar and unipolar patient groups were compared with those from the control group. Because the previously reported association of the I/D ACE polymorphism with affective disorder used a group comprising both bipolar and unipolar patients [Arinami et al., 1996], data from the bipolar and unipolar groups were also combined to give an “affective disorder” group. No significant association with this polymorphism was found in either disorder or in the combined affective disorder group (Table I).
DISCUSSION
The Japanese study of Arinami et al. [1996], using the ACE insertion/deletion polymorphism, reported that both the D allele (P < 0.02) and the DD genotype, compared with the DI + II genotypes (P < 0.002), were significantly more frequent in the combined bipolar and unipolar affective disorder group than in controls. Subdivision of this affective disorder group showed that the difference between cases and controls was more significant in the bipolar group. Our results failed to replicate the findings of this study, when either of the affective disorder groups were analyzed separately or together. These results do not support the ACE gene having a major role in the etiology of either bipolar or unipolar affective disorders. It is possible, however, that there is an effect of the ACE insertion/deletion polymorphism on the risk for affective diseases that may be confined to the Japanese population.
Acknowledgements
We thank Elizabeth Buckeridge and Caroline Crane for technical support and Dr. Sanjeev Jain for the collection of some bipolar samples. R.A.F. is a Peterhouse Senior Research Associate in Neuroscience, J.S.R. is a Betty Behrens Research Fellow at Clare Hall, Cambridge in receipt of a Sackler studentship, and D.C.R. is a Glaxo Wellcome Research Fellow. The collection of unipolar samples was conducted by L.H. during tenure of the Research Registrar post on the Cambridge Psychiatric Training Rotation. We also thank the Friends of Peterhouse, The Isaac Newton Trust, and the University of Cambridge Department of Pathology for funding.
