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College students in two separate studies had platelet monoamine oxidase (MAO) activity determinations and average evoked potential (AEP) measurements taken. On the basis of Minnesota Muliphasic Personality Inventory (MMPI) or Research Diagnostic Criteria (RDC) evaluations, psychopathology, particularly affective disorder, was found to be more prevalent among both persons with the combination of low MAO activity and AEP augmenting and those with high MAO activity and AEP reducing. The same pattern is apparent whether students were selected for extremely high or low MAO activity (study 1) or for elevated or normal MMPI scores (study 2). Some psychiatric patient groups also show this pattern. An interactive model of sensation-seeking and sensory inhibition is presented.

The present study, using a diathesis-stress model, attempted to confirm prior findings with platelet monoamine oxidase (MAO) activity and stress in a middle-aged, non-clinic population. One hundred and seventy-eight adult males from a statewide community club were tested for platelet MAO activity and stressful life events and were also given a variety of psychological measures of both psychopathology and psychosocial coping. The data were examined both for correlations across the total sample and for a comparison of high-risk groups (top and bottom 15% of MAO activity) with a middle MAO group. Low platelet MAO activity was related to a higher incidence of contact with mental health professionals, and more frequent use of alcohol and cigarette smoking. High MAO activity was related to higher levels of anxiety and somatization. High levels of stress were related to increased psychosocial problems reported for female and family members, higher scores on two schizophrenia-related MMPI scales (schizophrenia and paranoia subscales), but fewer idiosyncratic associations, elevated hypomanic, depression, and anxiety scores, increased alcohol use, and increased use of prescribed antianxiety and sedative medication. Neither MAO nor stress were related to current levels of psychosocial coping. Moreover, no interaction effects were uncovered for MAO activity and stress combined.

No differences in levels of type A monoamine oxidase (MAO) were observed in cultured human skin fibroblasts from nine patients with bipolar depressive illness as compared to 18 age-, sex-, and race-matched controls. All cells were biopsied and cultured under parallel conditions. Fibroblasts from monozygotic twins (three sets) had levels of MAO activity that were highly concordant, indicating that levels measured in fibroblasts are genetically determined. Together these findings suggest that an inherited predisposition to bipolar depressive illness does not involve inherited variations in levels of type A MAO activity. Using a larger control population, a positive correlation was observed between age of donor and level of MAO activity. This finding demonstrates the need for age-matched control and patient groups when comparing levels of type A MAO in fibroblasts.

A population of individuals potentially at risk for psychiatric disorders was identified by screening 375 college student volunteers for low platelet monoamine oxidase (MAO) activity levels. The lower and upper 10 per cent in MAO activity were interviewed and family history data were obtained. Low-MAO probands reported more frequent psychiatric or psychological counseling and problems with the law. Families of low MAO probands had an eightfold increase in the incidence of suicide or suicide attempts over those of high-MAO probands. This suggests that reduced MAO levels, reported previously in patients with affective disorders and chronic schizophrenia, may predict a vulnerability to psychiatric disorder.

The authors compared the correlation between platelet monoamine oxidase (MAO) activity and the Paranoia (Pa) scale of the Minnesota Multiphasic Personality Inventory in several groups. The data suggest that there is a positive association between high MAO activity and high scores on the Pa scale but only in samples with psychopathology.

Individuals potentially at risk for psychiatric disorders were identified by screening 375 college student volunteers for low platelet monoamine oxidase (MAO) activity levels. The lower and upper 10% in MAO activity were administered a personal and family history interview, psychological tests and average evoked response (AER) electroencephalographic procedures. Results indicated that low MAO males and females were socially more active, had more psychiatric contact, and had relatives who were psychiatrically more disturbed than high MAO subjects. Low MAO males had more convictions, experimented more with illegal drugs and had elevated scores on the MMPI. AER criteria further defined a high risk group of low MAO-AER augmenters which had more suicides among their relatives and higher scores on the schizophrenia scale of the MMPI.

This article examines current research strategies in biological psychiatry and the possible effects of biological heterogeneity on these strategies. First, the limited power of t test comparisons of measurements obtained from groups of patients and controls is demonstrated through a computer simulation. Second, we examine statistically the data from 14 recent platelet MAO studies to see if the heterogeneity in results of these studies could relate to an underlying biological heterogeneity. Finally, we suggest research methods we believe may be more useful than the current standard paradigm for elucidating the biological etiologies of psychiatric syndromes.

Increases in plasma prolactin concentrations produced by alpha-methyl-p-tyrosine, a catecholamine synthesis inhibitor, varied inversely with baseline platelet monoamine oxidase activity in 12 patients with chronic schizophrenia. In normal volunteers with low monoamine oxidase activity and in unmedicated patients with chronic schizophrenia, plasma prolactin concentrations varied directly with platelet monoamine oxidase activity. No such relationship was found in normal subjects with high platelet monoamine oxidase activity. These data suggest that platelet monoamine oxidase activity reflects monoaminergic activity in the tubero-infundibular system, which in turn affects plasma prolactin concentrations. This relationship may be important in patients with low platelet monoamine oxidase activity, such as some chronic schizophrenics.

The relationship between suicides and suicide attempts and two biological measures, platelet monoamine oxidase levels (MAO) and average evoked response (AER) augmenting, was examined in 79 off-medication psychiatric patients and in 68 college student volunteers chosen from the upper and lower deciles of MAO activity levels. In the patient sample, male individuals with low MAO and AER augmenting, a pattern previously associated with bipolar affective disorders, showed a significantly increased incidence of suicide attempts in comparison with either non-augmenting low MAO or high MAO patients. Within the normal volunteer group, all male low MAO probands with a family history of suicide or suicide attempts were AER augmenters themselves. Four completed suicides were found among relatives of low MAO probands where as no high MAO proband had a relative who committed suicide. These findings suggest that the combination of low platelet MAO activity and AER augmenting may be associated with a possible genetic vulnerability to psychiatric disorders.

The most widely replicated neurochemical finding in schizophrenia is that of lower levels of monoamine oxidase (MAO) in the platelets of chronic schizophrenics than in normal controls. Yet, the etiological role of MAO in schizophrenia remains to be demonstrated. The incidence of low MAO in other psychiatric disorders, effects of diet, hormones and drugs, and relationships of platelet MAO to brain levels and genetic mechanisms remain unclear. This article examines factors which make any biological indicator suitable for use as a diagnostic test for schizophrenia and inquires into the methodological pitfalls and unexamined assumptions of various research strategies which use this measure.

This study replicates and extends earlier work by finding that low levels of platelet monoamine oxidase (MAO) activity correlate with sensation seeking, high ego strength, positive affect, and high leisure time activity levels, somewhat similar psychological correlates also being found for plasma amine oxidase activity. Although there are several ways in which a schizophrenia/MAO relationship may exist and still be congruent with the present data, these results pose difficulties for theories which link low MAO activity levels specifically to schizophrenia. Nothing in the present findings, however, is incongruent with the possibility of an association between low platelet MAO activity and bipolar affective disorder.

A prospective investigation using platelet monoamine oxidase activity and cortical evoked response augmenting/reducing to predict the onset of new episodes of affective disorders was conducted in a college sample. During an 18-month period between clinical interviews, higher incidences of major depression and hypomania characterized the low MAO/aociated with affective psychopathology in the original retrospective study.

From an original sample of 375 college students and employees studied for platelet MAO activity, 66 subjects representing the lower and upper deciles of the sample were contacted for further study, including administration of the booklet form of the MMPI. We analyzed what psychological characteristics might be associated with differences in MAO activity and attempted to cross-validate these characteristics by using them to predict the separability of low vs. high MAO subjects. Each subject was randomly assigned to one of two groups in which the low and high MAO subjects were balanced for sex. For 16 women in group A, a MAO scale discriminated low and high subjects with 100% accuracy. For 18 men in group A, a separate MAO scale discriminated with 94% accuracy. To cross-validate these results, the two scales were applied to another population; both discriminated low and high MAO women and men with a combined 97% accuracy. The thematic content of the two scales is discussed in the light of other reports on the psychological characteristics of low and high MAO subjects, including the apparent relationship between the scale content and the clinical features of bipolar affective disorder.

Thirty-seven parents of probands with low platelet monoamine oxidase (MAO) activity levels and 38 parents of high MAO probands were examined for MAO activity, past and present psychopathology, and reported psychopathology in other relatives. Results showed generally positive and significant correlations between parents' and children's MAO levels, significantly greater rates of "high MAO related" disorders in parents and relatives of high MAO probands and of "low MAO related" disorders and symptoms in parents and relatives of low MAO probands. Support for a two-directional monoamine hypothesis of affective disorders is suggested.

In previous work, we have reported that specific combinations of platelet (MAO) activity and evoked potential augmenting/reducing (AR) are associated with risk for affective disorders. This new study screened 271 college freshmen solely on MAO and AR and selected a sample with extreme values on both measures. These students were interviewed with the Diagnostic Interview Schedule and they completed a family history questionnaire and psychosocial scales. Following the previous work, the same MAO and AR combinations were related to the frequency of major depression and a family history of psychiatric disorder.

College students hypothesized as being at risk for psychiatric dysfunction solely on the basis of their MAO platelet activities were briefly interviewed 2 years after completion of initial studies. These 33 low-MAO subjects reported more job instability than 30 high-MAO control subjects. Moreover, the low-MAO males had fallen about half a year behind their high-MAO counterparts in school. No differences in other aspects of social status or psychosocial problems had developed, although the low-MAO subjects smoked significantly more cigarettes and tended to report more major or minor medical problems. While the low-MAO subjects reported no significant decline in their own mental health status during this period, more low-MAO male subjects did report mental health problems in their families, especially depression, alcoholism, and suicide attempts, as well as significantly more mental health interventions among family members, such as psychiatric visits, prescription of psychotropic medication, and psychiatric hospitalization.