Studies on neurochemical heterogeneity in healthy parents of schizophrenic patients

Schizophrenia Research, IO (1993) 113-178 10 1993 Elsevier Science Publishers B.V. All rights reserved

SCHRES

173 0920-9964/93/$06.00

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Studies on neurochemical heterogeneity in healthy parents of schizophrenic patients Jun Wei, Hai-Min Inslitutr

Xu and Gwynneth

P. Hemmings

of BiologicalPsychiatry, Schizophrenia Association of Great Britain, Bangor, UK

(Received

6 September

1992; revision received and accepted

22 December

1992)

Serum homovanillic acid (HVA), norepinephrine (NE), phenylalanine (Phe) and tyrosine (Tyr) have been examined in 80 healthy parents of schizophrenic patients and 26 normal control subject. Analysis of variance revealed a significant difference in serum HVA concentration among the three groups: the parents whose ill offspring became fairly well after neuroleptic treatment for more than three months (n = 33) those whose offspring were still actively ill after neuroleptic treatment (n = 33) and normal control subjects (F = 3.98, df= 2, 89, p < 0.05). The t-test showed that serum HVA was significantly higher in the parents whose ill offspring became fairly well after neuroleptic treatment (11.8 f 5.0 ng/ml) than in normal control subjects (8.7k3.5 ng/ml, p 0.05). There was a significant difference between the serum NE concentrations of the parents of female patients (515 + 224 pg/ml, n = 21) and those of male patients (401+ 186 pg/ml, n= 55, p ~0.05). No significant differences were found in the serum concentrations of Phe and Tyr. These results suggest that there may be neurochemical heterogeneity in the parents of schizophrenic patients, which may be involved in the response of schizophrenic offspring to neuroleptic treatment and in the gender differences of schizophrenia. Key words: Homovanillic

acid; Norepinephrine;

Phenylalanine;

INTRODUCTION

It appears that a genetic component may be involved in schizophrenia (DeLisi and Lovett, 1990) but its mechanism of inheritance is still unknown. Sherrington et al. (1988) found that schizophrenia in seven British and Icelandic families is linked to a region of chromosome 5. However, Kennedy et al. (1988) failed to confirm this. In view of variables of the schizophrenic phenotype in affected individuals, such as the age of onset, duration and severity of illness, premorbid functioning, symptomatology, brain morpholfindings and response to ogy> neurochemical Correspondence to: J. Wei, Institute of Biological Psychiatry, Schizophrenia Association of Great Britain, Wellcome Building, Deiniol Road, Bangor, Gwynedd LL57 2UW, UK.

Tyrosine;

(Schizophrenia)

neuroleptic treatment, the genetic component related to schizophrenia may be heterogeneous. Many neurochemical abnormalities have been described in schizophrenia (Meltzer et al., 1984; DeLisi and Wyatt, 1985; Owen and Cross, 1992) but findings are always inconsistent. The genetic heterogeneity may contribute to the variables in the neurochemistry, which in turn are involved in the clinical expression of schizophrenia, although neurochemical changes may depend upon a clinical state as well (Van Kammen et al., 1985; Van Kammen and Schooler, 1990). The present study was designed to compare homovanillic acid (HVA), norepinephrine (NE), phenylalanine (Phe) and tyrosine (Tyr) in the serum of healthy parents, who were divided into two groups on the basis of the response of their schizophrenic offspring to neuroleptic treatment,

174

with normal control subjects, and also to compare these parameters between the parents of male and female schizophrenic patients. Data on the serum HVA, NE and dopamine b-hydroxylase of the patients in this study have been published previously (Wei et al., 1992). We examined whether there was a genetic component related to the response of schizophrenic patients to neuroleptic treatment, or to the gender differences of schizophrenia.

METHODS Subjects Eighty healthy parents (33 fathers and 47 mothers), aged 39-75 years, accompanied by their schizophrenic offspring (whose diagnoses had been made by the psychiatrists who initially treated them, and confirmed here during a more than 2 h interview with them), and 26 normal control subjects (12 males and 14 females), aged 40-69 years, came to the Schizophrenia Association of Great Britain (SAGB) in Bangor, North Wales, from all parts of the United Kingdom. The parents were divided into two groups, 23 parents of female patients (11 fathers and 12 mothers) and 57 parents of male patients (22 fathers and 35 mothers). Also, 66 of the parents of schizophrenic patients who had been taking neuroleptic drugs for longer than six months (except one who had been taking the drug for three months), were divided into two groups, group A and group B, based on the clinical states of their ill offspring at the time of the interviews and clinical examination. The severity of the clinical states was scored by a rating scale described in a previous study (Wei et al., 1992). Group A consisted of 33 parents (13 fathers and 20 mothers) whose ill offspring were in remission, working or capable of work full time, or were slightly psychotic; Group B consisted of 33 parents (12 fathers and 21 mothers) whose offspring were still actively ill, not capable of work, or with visibly psychotic symptoms. All the volunteers travelled the day before the blood samples were taken and did not eat from 22:00 h of that day until the blood was drawn 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. The normal

control subjects did not have schizophrenic tives in their families.

rela-

Blood collection and separation The subjects all signed the consent forms for taking blood samples, and remained sitting for 15-20 minutes prior to blood collection. Venous blood was drawn from the ante-cubital vein between 8:00 and 9:00 in the morning and cooled to 2-4°C immediately. The serum was separated by centrifugation at 4°C and 2000 rpm for 15 minutes and then stored at -45°C until the samples were measured within 10 weeks. Sample determination Serum NE was measured by the method described in a previous study (Wei et al., 1992). To process serum samples for measurements of HVA, and phenylalanine and tyrosine by high performance liquid chromatography (HPLC), 0.4 ml of 0.5 M perchloric acid was added to 0.6 ml serum in an Eppendorff tube, and well mixed. The samples were centrifuged at 10,000 g for 20 minutes. The supernatants were collected and then filtered through a membrane filter with 0.3 pm pore (Whatman, UK). HPLC with electrochemical detection was used to measure HVA by the method described previously (Wei et al., 1992). Phenylalanine and tyrosine were measured by a reversed-phase HPLC with ultraviolet (UV) detection. The UV wavelength for simultaneously detecting the two amino acids was 210 nm. Integration of the chromatograms was performed with an integrator (LA 500, Trivetor, UK). The concentrations of phenylalanine and tyrosine in serum were calibrated by using external standards, the concentrations of which were linear within the range of 5-25 pg/ml. The mean coefficients of variation for multiple samples repeatedly measured on different days were less than 8% for both amino acids. The samples were run blindly. Values used were the means of duplicate determinations. Analysis of variance and a two-tailed t-test were used for processing data. RESULTS Analysis of variance revealed a significant difference of serum HVA concentration among group A,

175

group B and normal control subjects (F= 3.98, df= 289, p < 0.05), and the f-test showed that the serum HVA concentration was significantly higher in group A than in normal control subjects (p < O.Ol), but was not significantly higher in group B than in normal control subjects (p > 0.05). No significant differences were found between the three groups in the concentrations of serum NE, phenylalanine and tyrosine (Table 1). There was a significant difference between the serum NE concentrations of the parents of male patients and those of female patients (p< 0.05), but no significant differences were found between the two groups in the concentrations of serum HVA, phenylalanine and tyrosine (Table 2).

DISCUSSION

The heterogeneity of schizophrenia seems to have been recognised (Tsuang et al., 1990), as there are differences among affected individuals in clinical symptoms (Andreasen and Olsen, 1982; PogueTABLE

Geile and Harrow, 1984), duration of illness (acute brain abnormalities and chronic), structural (Keshavan and Ganguli, 1990) and the response to neuroleptic treatment (Chang et al., 1988, 1990; Chen et al., 1989). Chen et al. (1989) reported that the pretreatment concentration of plasma HVA in schizophrenic patients who had a good response to neuroleptic treatment was higher than that in those who had a poor response to neuroleptic treatment. This finding suggests that the response to neuroleptic treatment may be related to dopaminergic activity in schizophrenia. Circulating HVA may partly reflect dopaminergic activity in the brain, although caution is needed in interpreting this (Picker et al., 1988). That is because about half the HVA in the circulation is considered to derive from this source (Sternberg et al., 1983), particularly under the conditions of controlled diet and physical activity, which minimise exogenous or peripheral contributions to circulating HVA (Kendler et al., 1983; Davidson et al., 1987). Whether the clinical variables of schizophrenia depend on the genetic heterogeneity remains unknown, dopaminergic overactivity, as a major

1

Concentrations of serum HVA, NE, Phe and Tyr in the parents whose ill offspring had been taking neuroleptic drugs Measurements

Group A

HVA (ng/ml) NE (pg/ml) Phe kg/ml) Try @g/ml)

Control

Mean + S. D.

n

Mean + S.D.

n

Mean + S.D.

n

11.8k5.0** 410& 198 9.8k 1.0 12.41i: 1.9

33 32 31 31

lOSk3.7 426+215 9.6kl.l 11.9kl.9

33 31 29 29

8.7+ 3.5 438rfr 163 9.6* 1.2 12.Ok2.1

26 22 25 25

Group A: their ill offspring Group B: their ill offspring **Two-tailed r-test, ~~0.01 TABLE

Group B

had a good outcome had a poor outcome (vs. control).

from neuroleptic from neuroleptic

treatment. treatment.

2

Concentrations of serum HVA. NE, Phe and Tyr in the parents of schizophrenic men and women Measurements

HVA (ng/ml) NE (pgiml) Phc kg/ml) Tyr &g/ml) *Two-tailed

Parents of male patients

Parents of female patients

Mean If: S.D.

n

Mean i S.D.

n

10.6k4.4 401 f 186 9.9& 1.3 12.1+ 1.7

57 55 51 51

11.6k3.7 515+223* 9.7* 1.0 12.2k2.1

23 21 23 23

t-test, p < 0.05 (vs. parents

of male patients).

176

finding in supporting the dopamine hypothesis of schizophrenia (Reynolds, 1989) may be related to a genetic component. Sedvall and Wode-Helgodt (1980) reported that the schizophrenic patients with a family history of the illness had higher levels of HVA in cerebrospinal fluid (CSF) than did those with no such family history. Sedvall et al. (1980) also reported that normal individuals with a family history of schizophrenia had higher levels of CSF HVA than did those with a family history of depressive disorder. They suggested that CSF monoamine metabolite determination was valuable for the prediction of family vulnerability to psychiatric morbidity in healthy subjects. However, Oxenstierna et al. (1986) found that familial heritability for HVA and 5-HIAA in the CSF was more influenced by the cultural than the genetic component. The present study demonstrates that the serum HVA concentration was significantly higher only in the parents whose ill offspring had become fairly well after neuroleptic treatment, but not in those whose offspring were still actively ill, as compared with normal control subjects (Table 1). These data suggest that dopaminergic overactivity found in schizophrenia may be determined partially by genetic transmission, or may be a genetic marker of a subgroup of schizophrenia. In this study, we did not find a significant difference of serum HVA concentration between the parents whose ill offspring were fairly well after neuroleptic treatment and those whose offspring were still actively ill (Table 1). A possible explanation for this is that the clinical states of the patients, who had been taking neuroleptic drugs at home for at least three months, were assessed only once when they were interviewed at the time of collection of their blood samples in the SAGB Institute of Biological Psychiatry, and we could not confirm independently whether they had been taking the neuroleptic drugs as prescribed. This may influence the assessment of neuroleptic treatment, especially in the patients who were still actively ill. However, a trend towards the difference of serum HVA concentration between the two parent groups divided according to the clinical states of their ill offspring with neuroleptic treatment (Table 1) indicates that they may have a different genetic basis for dopamine turnover. There is evidence indicating gender differences in schizophrenia, especially in the age of onset,

severity of illness and symptomatology (Seeman, 1986; Goldstein and Link, 1988; Hafner et al., 1989; Thara and Rajkumar, 1992; Shtasel et al., 1992). The age of onset is earlier in schizophrenic men than in schizophrenic women (Hafner et al., 1989); male patients are more severely ill than are female patients (Goldstein and Link, 1988), and men have a poorer premorbid picture and a poorer outcome than women (Gittelman-Klein and Klein, 1969; Huber et al., 1980; Salokangas, 1983; Seeman, 1986; Goldstein, 1988). Although gender differences in schizophrenia may be due to physiological factors, we cannot rule out the possibility that genetic factors contribute to the gender differences in the etiology. Recent studies have demonstrated that relatives of female probands are at higher risk for schizophrenia than those of male probands (Goldstein et al., 1990, 1992). The present study indicates a significant difference in serum NE between the parents of male and female patients (Table 2), suggesting that sympathetic excitability of the parents of female patients may be higher than that of the parents of male patients. This may be a genetic clue in studying the etiology of schizophrenia in females, although the genetic relationship between the sympathetic excitability of the parents of schizophrenic patients and the pathogenesis of schizophrenia is not clear. Circulating phenylalanine and tyrosine, as precursors of catecholamines, affect the biosynthesis of catecholamines in the brain (Fernstrom, 1990). Since Perry et al. (1973) reported that phenylketonuric adults with normal intelligence had schizophreniform episodes, the heterozygotic carriers of phenylketonuria have been considered to be at high risk for the development of schizophrenia (Potkin et al., 1983). One might expect that abnormal concentrations of phenylalanine and tyrosine in the circulation should be found in their parents if some schizophrenic patients were heterozygotic carriers of phenylketonuria. However, we did not find significant changes in serum concentrations of phenylalanine or of tyrosine in the parents of any group of the patients (Tables 1, 2). Taken together, the different findings obtained from a number of studies on schizophrenia in its symptomatology, morphology, neurochemistry and psychopharmacology may be related to genetic heterogeneity. The present study suggests that there may be neurochemical heterogeneity in the

177

parents of schizophrenic patients, and this is likely to be involved in the response of their ill offspring to neuroleptic treatment and in the gender differences of schizophrenia.

ACKNOWLEDGEMENTS

The authors wish to thank Dr. H. Hillman, Medical Adviser, for interviews with the volunteers and for collecting blood samples, as well as all the staff of the Schizophrenia Association of Great Britain for their help in this study.

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