Are gender differences genetically related to catecholamine metabolism in schizophrenia?

J.p.sychiat. Res., Vol. 27, No. 4. pp. 35S360, 1993 Copyright 0 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0022%3956/93 %6.00 + .I0

Pergamon

ARE GENDER DIFFERENCES GENETICALLY RELATED TO CATECHOLAMINE METABOLISM IN SCHIZOPHRENIA? JUN WEI, C. N. RAMCHAND and GWYNNETH P. HEMMINGS Institute

of Biological

Psychiatry, Schizophrenia Association of Great Britain, Wellcome University of Wales, Bangor, Gwynedd LL57 2UW, UK. (Receivedfor

publication

Building,

Science Site,

5 August 1993)

Summary-Serum homovanillic acid (HVA) and norepinephrine (NE), serum dopamine- /I-hydroxylase (DBH), platelet monoamine oxidase (MAO), and erythrocyte catechol-0-methyltransferase (COMT) have been measured in 86 healthy parents of schizophrenic patients and 36 normal control subjects. The t-test showed that serum HVA concentration was significantly higher in mothers of female patients than in mothers of male patients (p < ,051); Kruskal-Wallis analysis revealed a significant difference in erythrocyte COMT activity among the mothers of male patients, mothers of female patients and female control subjects (H = 8.7, df = 2, p -C .02); and the Mann-Whitney test demonstrated that erythrocyte COMT activity was significantly increased in mothers of male patients as compared with female control subjects (p < .Ol), but there were no significant differences in the HVA concentration and COMT activity between the fathers of male and female patients, and male control subjects. There were no significant changes in serum NE concentration, serum DBH and platelet MAO activity in these subjects. The present study suggests that catecholamine metabolism in mothers of schizophrenic patients may play a genetic role in the gender differences of schizophrenia.

Introduction many differences in clinical expression between male and female schizophrenic patients. Men have an earlier age of onset, a poorer premorbid history, more negative symptoms, differential neurocognitive functioning, a poorer course, a poorer response to neuroleptic drugs, a lower family morbidity risk, and differential structural and functional brain abnormalities compared with schizophrenic women (for review, see Goldstein & Tsuang, 1990). The gender differences might reflect the heterogeneity of the illness (Goldstein, Tsuang, & Faraone, 1989). In view of the involvement of a genetic component in schizophrenia (DeLisi & Lovett, 1990), the genetic contribution to gender differences should not be ruled out in studying the aetiology of schizophrenia. Crow (1983) reported that the concordance rate for schizophrenia was higher in same-sex than in different-sex dizygotic twin and sibling pairs. Several reports indicated that the relatives of female probands were at higher risk for schizophrenia than those of male probands (Bellodi et al., 1986; Shimizu, Kurachi, Yamaguchi, Torii, & Isaki, 1987; Goldstein, Faraone, Chen, Tolomiczencko, & Tsuang, 1990; Pulver et al., 1992; Wolyniec, Pulver, McGrath, & Tam, 1992). In a previous study, we found that concentrations of serum norepinephrine (NE) were significantly higher in the parents of female patients than in those of male patients (Wei, Xu, & Hemmings, 1993). To carry out a further study on a genetic relationship between catecholamine metabolism and gender differences of schizophrenia, the present work was undertaken to measure THERE

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J. WEI et al.

serum homovanillic acid (HVA) and NE, serum dopamine- B-hydroxylase(DBH), platelet monoamine oxidase (MAO), and erythrocyte catechol-0-methyltransferase (COMT) in healthy parents of female and male patients, and in normal control subjects.

Methods Subjects Eighty-six healthy parents of schizophrenic patients, aged 38-69 years (56.8 + 7.5 years), and 36 normal control subjects, aged 38-70 years (52.6 f 9.1 years), came voluntarily to the Schizophrenia Association of Great Britain from all parts of the United Kingdom. They travelled the day before the blood samples were taken, and did not eat from 10.00 p.m. of that day until after drawing the blood the next morning. They were asked about their medical histories, including mental and physical illnesses, infectious diseases and about any drugs they were taking for therapeutic, nutritional, or addictive reasons. No one had been included in this study, if they had been suffering from any mental illness or severe physical disease, or if they were taking any drugs which affect the nervous system. The normal control subjects did not have schizophrenic relatives.

Collection and determination

of’ blood samples

The subjects all signed consent forms for taking blood samples, and remained sitting for 15520 minutes prior to blood collection. About 20 ml of venous blood was drawn from the ante-cubital vein between 8:00 and 9:00 a.m. the morning, and the blood was put into heparinised, K+ EDTA or plain plastic tubes, respectively. They were cooled to 24°C immediately. Samples of 2 ml with K+ EDTA were centrifuged at 4°C 300 g for 20 minutes to prepare platelet-rich plasma. Platelet MAO was assayed using the method described by Murphy et al. (1976). Benzylamine was used as substrate at a final concentration of 0.22 mmol/L. A sample of 1.5 ml of the heparinised blood was centrifuged at 4°C 6,500 g for 15 minutes to obtain packed red blood cells, and the erythrocyte COMT was measured using the procedure described by Gershon and Jonas (1975). S-adenosylmethionine was used as substrate at a final concentration of 0.02 mmol/L. The serum for measuring DBH, HVA and NE was separated by centrifugation at 4°C 2,000 rpm for 15 minutes. The serum DBH was determined based on the procedure reported by Nagatsu and Udenfried (1972) and the tyramine was used as substrate at a final concentration of 36.4 mmol/L. The serum HVA and NE were analysed by high performance liquid chromatography (HPLC) with electrochemical detection, as described in a previous study (Wei, Ramchand, & Hemmings, 1992). All the samples were stored at ~ 45°C for not more than 10 weeks before measurements were made, and they were measured blindly and in duplicate. Analysis of variance (ANOVA) and the two-tailed t-test were used to process the data of serum HVA and NE, and KruskalWallis analysis and the Mann-Whitney I/ test were used to process data of these three enzymes.

GENDER AND CATECHOLAM~NEMETABOLISM

357

Results There was a higher concentration of serum HVA in mothers of female patients than that in mothers of male patients (p < .05). The concentration of serum NE was found to be higher in the parents of female patients compared with those of male patients or with normal control subjects, but this was not significant (Table 1). Table 1 Concentrations Subjects

of Serum HVA and NE in Healthy Parents of Schizophrenic

Parents of male patients Measurements

Male Female NE @g/ml) Male Female *p < .05 (vs mothers

Patients and Normal Control

Parents of female patients

Control subjects

Mean f SD

N

Mean + SD

N

Mean k SD

N

9.8 +4.8 9.6*4.2

23 39

10.7k3.3 12.1&3.7*

IO 14

8.7 * 3.4 9.5k3.8

18 18

413+147 3595 182

23 37

518&202 465 + 205

10 14

453* 180 340 + 106

18 15

of male patients,

two-tailed

t-test).

The activity of erythrocyte COMT was found to be significantly increased in mothers of male patients compared with female control subjects 0, < .Ol). No significant differences of activity of serum DBH and platelet MAO were found between these three groups (Table 2). Kruskal-Wallis analysis among these three groups

revealed a significant difference in erythrocyte COMT activity (H = 8.7, df = 2, p < .02), but no significant differences in the

Table 2 Activity of serum DBH, erythrocyte COMT Patients and Normal Control Subjects

and Platelet

Parents of male patients Enzymes DBH (nmol/ml/hr) Male Female COMT(nmol/ml packed cells/hr) Male Female MAO (nmol/lOs platelets/hr) Male Female

N

Mean

21.9&11.7 22.7* 11.2

21 33

23.0* 22.0*

13.8k6.9 13.3f6.1*

17 32

24.9 k20.9 21.7&11.2

14 22

subjects,

in Healthy

Parents of female patients

Mean f SD

*p < .Ol (vs female control

MAO

+

Parents of Schizophrenic

Control subjects

SD

N

Mean f SD

N

16.2 11.8

9 12

23.4+ 14.3 18.9*9.1

13 12

15.9k8.8 10.7*3.9

6 11

11.8+6.3 8.7*5.1

15 15

19.8+ 15.5 24.8k9.0

4 6

19.1 f 10.6 17.6+11.1

13 15

Mann-Whitney

U test, two-tailed).

358

J. WEI et al.

activity of serum DBH or platelet MAO. ANOVA did not show a significant concentrations of serum HVA and NE among these three groups.

difference

in

Discussion Since a considerable amount of HVA in the circulation derives from the brain (Sternberg, Heninger, & Roth, 1983), particularly under conditions of controlled diet and physical activity, which minimise exogenous or peripheral contributions to circulating HVA (Kendler, Mohs, & Davis, 1983; Davidson et al., 1987) the circulating HVA could be used as a possible index of central dopamine neuronal activity (Amin, Davidson, & Davis, 1992). Also, the HVA, as a major metabolite of dopamine, may directly reflect dopamine turnover or metabolism in the brain as well as periphery. The dopamine metabolism may be strongly influenced by inheritance in the families with schizophrenic patients, as schizophrenia is likely to be aetiologically related to a genetic component thereby causing dopaminergic overactivity in the central nervous system (DeLisi & Lovett, 1990). Sedvall et al. (1980) reported that normal individuals with a family history of schizophrenia had higher levels of HVA in the cerebrospinal (CSF) than did those with a family history of depressive disorder. They also found that schizophrenic patients with a family history of schizophrenia had higher levels of CSF HVA than did those with no such family history (Sedvall & Wode-Helgodt, 1980). In previous studies, we found that serum HVA was significantly higher in the parents whose schizophrenic offspring had a good response to neuroleptic treatment, but was not higher in those whose schizophrenic offspring had a poor response to neuroleptic treatment, than it was in normal control subjects (Wei et al., 1993). We also found that the first-degree relatives of schizophrenic patients with a late-onset age (20 years old and over) had a higher concentration of serum HVA than did those of the patients with an onset before 20 years of age (unpublished data). These data suggest that alteration of dopamine metabolism is likely to be a genetic marker for subgroups of schizophrenia. Furthermore, the present study showed that serum HVA concentration was significantly higher in mothers of female patients than in those of male patients (Table 1). It is possible that the gender differences regarding age of onset, response to neuroleptic treatment, etc., are genetically related to dopamine turnover. COMT is one of the metabolic enzymes involved in catecholamine catabolism and its activity is genetically controlled (Weinshilboum, 1983). It has been reported that the correlation coeffeicients of erythrocyte COMT activity were from 0.90 to 0.95 between monozygotic twins (Grunhaus, Ebstein, Belmaker, Sandler, & Jonas, 1976; Winter, Herschel, Propping, Friedl, & Vogel, 1978). The present study showed that erythrocyte COMT activity was significantly increased only in mothers of male patients, as compared with female control subjects (Table 2). This finding suggests that a disturbance of catecholamine metabolism, which is found in schizophrenia (van Kammen & Kelley, 1991), may be influenced by a different mechanism of the inheritance of genes between male and female patients, and this may be a genetic and biochemical basis for gender differences in the clinical expression of schizophrenia. However, COMT is controlled by an autosomal gene which is mapped to chromosome 22 in humans (Brane, Bannetta, Meera Khan, Arwert, & Serra, 1986). It would be worthwhile investigating whether the COMT activity

GENDER

AND CATECHOLAMINEMETABOLISM

359

could be regulated by some products, which are encoded by the genes on the sex chromosomes. The MAO and DBH activities are also controlled by inheritance (Weinshilboum, 1983). In this study, however, we did not find a significant difference in platelet MAO and serum DBH activity among these three groups. Possibly, the gender differences in schizophrenia are not related to the genetic mechanism of MAO and DBH. Acknowledgements-We wish to thank Dr. H. Hillman, the medical adviser, and the other staff of the Schizophrenia Association of Great Britain for their help in this study.

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