Genetic control of platelet monoamine oxidase activity: studies on normal families

Genome screen for platelet monoamine oxidase (MAO) activity

To identify loci involved in the control of platelet monoamine oxidase B (MAO-B) activity, a genomewide linkage screen was performed using 291 markers in 148 nuclear families containing a total of 1,008 nonindependent sib-pairs. Participants were genotyped and their platelet MAO-B activity levels were measured as part of the Collaborative Study on the Genetics of Alcoholism (COGA). Sib-pair analysis using Haseman-Elston regression was carried out with two programs. Two-point analysis on all pairs with SIBPAL indicated three markers with p-values below 0.01: D6S1018 (p = 0.0004), D2S1328 (p = 0.008), and D2S408 (p = 0.003). MAPMAKER/SIBS multipoint analyses using independent pairs(N = 409) gave maximal lod scores of 2. 0 on chromosome 6 and 1.1 and 1.4 for the two regions on chromosome 2. These results are consistent with linkage, but do not provide definitive evidence. We are currently creating a denser map in these regions and have begun genotyping a second sample in COGA.

Platelet monoamine oxidase B activity in dementia. A 4-year follow-up

Platelet monoamine oxidase B (MAO-B) activity has been found to increase significantly in demented patients. For the first time, a 4-year follow-up of platelet MAO-B activity and Mini-Mental State (MMS) was performed in patients with probable dementia of the Alzheimer type (DAT) and age-matched controls. MAO-B activity of DAT patients increased significantly 2 years after the beginning of the study as compared with controls and remained significantly higher for the entire period of the examinations (p < 0.0001). The decrease of the MMS scores did not correlate with the time course of the increase of platelet MAO-B activity (Spearman rank correlation test). The decline of the MMS scores of DAT patients preceded the elevation of MAO-B activity. Since degenerative processes in brain areas which are responsible for cognitive function and are reflected by the MMS scores rather affect cerebral cholinergic than monoaminergic neurotransmitter systems, degeneration of the latter at late stages of DAT might be reflected by increased platelet MAO-B activity.

Platelet monoamine oxidase (MAO) activity and alcoholism: is there a genuine association?

Monoamine oxidase (MAO) is a particle-bound flavoenzyme principally located in the outer mitochondrial membrane, which catalyzes the oxidative deamination of a variety of the amine transmitters in the central nervous system. There have been many reports from different groups around the world over the last 20 years that indicated a lower platelet MAO activity was associated with alcoholism. As there are multiple influences upon measured MAO activity, this article attempts to address each of the issues in turn for potential confounding of the reported association. These issues include: the duration of abstinence from alcohol, the substrate used for analysis, gender issues, association with different subtypes of alcoholics, the influence of other psychopathology, personality traits of alcoholics, the question of smoking, and proposed modes of transmission of MAO activity. The initial promise about MAO activity being a possible marker for alcoholism or a least a genetically predisposed subgroup has receded as the number of negative typology-based studies increases. The failure to account for a major confounding variable, e.g. smoking and other minor but possibly vital confounds in almost all these studies leaves the whole hypothesis open to criticism. However, the possible association between personality traits that might predispose to some if not all substances of addiction to low MAO activity may make it possible to reframe the hypothesized association in the setting of a generalized predisposition to addictions in particular, and to psychopathology in general. Nonetheless the association remains of great interest and may yet yield vital genetic and clinical information.

Alcohol consumption: biochemical and personality correlates in a college student population

The frequency of alcohol use among a subject population of 28 male and 60 female college students was assessed using the Student Alcohol and Drug Use Survey (STADUS). Data were also collected on personality traits as measured by the Sensation Seeking Scale V (SSSV) and the Eysenck Personality Questionnaire (EPQ). Finally, three biochemical variables were assessed: monoamine oxidase (MAO) activity, dopamine beta hydroxylase (DBH) activity, and testosterone levels. Among males, high SSSV scores, high testosterone levels, and low MAO activity contributed to the variance in alcohol use, whereas among females, a significant proportion of the variability in alcohol use was accounted for by high SSSV scores, high DBH activity, and younger age.

Ethanol, monoamines, and affect

Evidence suggests that ethanol self-administration is directly related to central norepinephrine (NE) activity and inversely related to central serotonin (5-HT) activity. Normal male volunteers participated in a placebo controlled crossover design to assess the effects of 1-tyrosine (TY) and 1-tryptophan (TP) (precursors of catecholamines and 5-HT, respectively) in combination with ethanol, on several neurobehavioral measures. Ethanol by itself produced negative effects on several dimensions of mood. Dysphoria was potentiated by TP in combination with ethanol and either unchanged or attenuated by the combination of TY and ethanol. Ethanol impaired verbal recall, and neither TP nor TY in combination with ethanol altered that impairment. The results are consistent with the hypothesis that 5-HT mediates some of the negative mood effects produced by ethanol or antagonizes some of its positive effects, while NE at least partly mediates ethanol's positive effects on mood. Ethanol's impairment of verbal memory appears to be mediated by mechanisms outside the monoamine systems.

Importance of genetic effects for monoamine oxidase activity in thrombocytes in twins reared apart and twins reared together

The relative importance of shared genes, shared environments, and individual specific environmental effects for monoamine oxidase (MAO) activity in thrombocytes was assessed in the Swedish Adoption/Twin Study of Aging. The sample consists of identical twins separated at an early age and reared apart (30 pairs), identical twins reared together (60 pairs), fraternal twins reared apart (66 pairs), and fraternal twins reared together (68 pairs), whose average age was 63.5 years; 49% were female. Consistent with the literature, the heritability of MAO activity was 0.77 and did not differ across cohort (under or over 63 years of age) or gender. Sharing rearing environments or similar experiences later in life does not result in familial similarity for MAO activity.

Monoamine oxidase and cortisol response in depression and schizophrenia

The relationship between hypothalamic-pituitary-adrenal (HPA) axis function and platelet monoamine oxidase (MAO) activity was examined in drug-free depressed (n = 32) and schizophrenic (n = 36) inpatients. HPA function was measured by determining plasma cortisol levels at 8:30 a.m. and 11 p.m. before, and 8:30 a.m., 4 p.m., and 11 p.m. after administration of 1 mg of dexamethasone (DEX). There was a significant correlation between platelet MAO activity and all post-DEX cortisol levels (8:30 a.m., 4 a.m., and 11 p.m.) in depressed patients, and MAO activity and pre-DEX cortisol levels (11 p.m.) in schizophrenic patients. MAO activity was significantly higher in depressed DST nonsuppressors than in suppressors, and there were more DST nonsuppressors in high-MAO groups as compared with low-MAO groups. Our results thus suggest a strong relationship between platelet MAO activity and HPA function in depressed patients. These biochemical markers are potentially useful in the identification of biochemically and clinically homogeneous subgroups of depressed patients.

Platelet MAO-B activity and vitamin B12 in old age dementias

Platelet MAO-B activity, serum vitamin B12 levels, and plasma folate were measured in patients suffering from presenile (AD) and senile (SDAT) dementia of Alzheimer-type, and vascular dementia (VD). MAO-B was higher in the SDAT group than in AD and controls. An inverse relationship between MAO-B activity and vit. B12 levels was documented in the whole group and in each category studied; furthermore, MAO-B was positively related to age. All the patients were then divided into two groups, according to vit. B12 levels (Group I: less than 200 pg/mL; Group II: greater than or equal to 200 pg/mL); Group I showed a significantly higher MAO-B activity with respect to Group II. The results indicate the existence of a negative association between platelet MAO-B activity and serum levels of vitamin B12 and confirm the existence of biological differences between presenile and senile dementia of Alzheimer type.

Vitamin B12-induced reduction of platelet monoamine oxidase activity in patients with dementia and pernicious anaemia

Platelet monoamine oxidase (MAO) activity has previously been shown to be increased in patients with senile dementia of Alzheimer type (SDAT) and in patients with megaloblastic anaemia. Moreover, low serum B12 levels were found to be 4-5 times more frequent in SDAT compared with an unselected population of similar age. In the present investigation, platelet MAO activity was estimated in 14 SDAT patients with relatively low serum B12 levels and in 4 patients with pernicious anaemia. Before B12 therapy, platelet MAO activity was significantly increased in both patient groups compared with a control group. After B12 therapy, platelet MAO activity was significantly reduced in both patient groups to apparently normal levels. The present results show that B12 status is a controlling factor of platelet MAO activity and confirm that a significant connection exists between vitamin B12 deficiency and primary degenerative dementia disorders, such as SDAT.

EEG sleep, lithium transport, dexamethasone suppression, and monoamine oxidase activity in borderline personality disorder

Twenty-one patients who met DSM-III criteria for borderline personality disorder (BPD) and also scored at least 7 on the Diagnostic Interview for Borderlines (DIB) were assessed on four biological markers: electroencephalographic (EEG) sleep, in vitro lithium ratio, platelet monoamine oxidase (MAO), and dexamethasone suppression test (DST). REM latency averaged 58.66 (SD 14.39); platelet MAO averaged 21.74 (SD 10.33); and lithium ratio was 0.357 (SD 0.139) in the BPD patients. All of those values were significantly abnormal. Many patients had abnormalities on three or four measures. These patients in general had multiple Axis I diagnoses from the Diagnostic Interview Schedule (DIS), and these Axis I diagnoses tended to produce patient clusters. Patients with a DIS diagnosis of schizophrenia, mania, hypomania, or schizoaffective mania had elevated lithium, low MAO, and normal EEG sleep, while those patients with coexisting major depression tended to have short rapid eye movement (REM) latency, high REM density, and normal MAO and lithium ratio. Only two patients were nonsuppressors on the DST, confirming recent reports of normal DST results in personality disorders.

Platelet monoamine oxidase in alcoholism

We studied platelet monamine oxidase (MAO) activity using 14C-tyramine as substrate in hospitalized alcoholic patients in the early phases of abstinence and in nonhospitalized normal control volunteers. Platelet MAO was determined in 75 patients (67 men, 8 women) with alcoholism and 123 normal control volunteers (52 men, 71 women). The platelet MAO activity in alcoholic patients was significantly lower than in normal control volunteers. We also observed that the mean platelet MAO activity in male alcoholics was significantly lower than in normal males. The analysis of platelet MAO in alcoholics revealed a mixture of two normal distributions. Alcoholic patients falling into the low MAO component were younger in age, with a lower age of onset of alcoholism, and had higher frequencies of family history of alcoholism. They thus resembled type II alcoholics described by other investigators. Platelet MAO may thus serve as a useful biological marker for subtyping alcoholism and identifying high-risk groups at an early stage. The findings of this study are consistent with previous reports of low platelet MAO activity in alcoholic patients.

Genetics of schizophrenia: II. Vulnerability traits and gene markers

The author reviews research strategies for identifying biological vulnerability traits and gene markers. The application of these methods to schizophrenia are discussed. He concludes that, based on the available evidence, none of the proposed biological traits qualifies as a major factor in the genetic susceptibility to schizophrenia. Some of these traits (such as attentional, neurophysiological, and brain morphology measures) appear promising, but the data are inadequate to arrive at a firm conclusion. Studies with gene markers have not produced consistent results. The author presents the methodological issues that concern this area of research and offers recommendations for future studies.

Measurement of platelet monoamine oxidase using three different substrates in patients with alcoholism and schizophrenia

The platelet monoamine oxidase (MAO) activities in alcoholism and schizophrenia were investigated by means of simultaneous determination, using beta-phenyl-ethylamine, tryptamine and serotonin as substrates. No significant difference was found between the MAO levels in the alcoholic and schizophrenic groups, when tryptamine was used as a substrate, but both groups showed lower values than the controls. On the other hand, beta-phenylethylamine, a specific substrate for MAO B used as a substrate, showed no significant difference between the alcoholic and control groups in the activities. These two groups showed higher values in MAO activity than the schizophrenic group, whereas when MAO activity was estimated using serotonin, platelet enzyme was found to be inhibited significantly in alcoholism, and the level of activities in the schizophrenics was similar to that of the controls. Moreover, the beta-phenylethylamine inhibition curve obtained serotonin as the substrate in the pooled platelets of 50 normal human subjects, and the MAO activity could not be inhibited by higher concentrations than the Km value of serotonin. These findings suggested that there might be two interacting catabolic sites having different substrate affinities in blood platelet MAO. Thus, it could be speculated that serotonergic catabolic sites of MAO in the platelets are disturbed in the alcoholics, while beta-phenylethylaminergic catabolic sites of platelet MAO are inherently vulnerable in schizophrenia.

Morbidity risk for psychiatric disorders in families of probands with affective disorders divided according to levels of platelet MAO activity

In a series comprising 166 subjects with affective disorders, the lowest and highest quartiles in the male and female platelet monoamine oxidase (MAO) distribution, respectively, were included. The morbidity risk in the first-degree relatives (parents and siblings) of these low and high platelet MAO subjects was determined. First-degree relatives of low platelet MAO probands were found to have an increased morbidity risk for neurotic-reactive depressions and for alcoholism. The results seem to be in line with the biological high-risk paradigm, indicating that platelet MAO could be a biological marker for increased vulnerability. First-degree relatives of high platelet MAO probands were found to have an increased morbidity risk for bipolar affective disorders.

Genetic analysis of platelet monoamine oxidase activity in families of schizophrenic patients

Platelet monoamine oxidase (MAO) has been implicated in the biology of several psychiatric disorders, including schizophrenia. Genetic factors contribute to the variance of MAO activity; however, its mode of inheritance is unknown. To assess the distribution and familial patterns of platelet MAO activity, we studied 73 chronic schizophrenic patients and 219 of their first-degree relatives. The activity distribution was skewed and admixture of two distributions gave a better fit to the data than a single distribution. Single-major-locus hypotheses were tested by pedigree analysis methods for quantitative traits. Using the transmission probability model, the familial transmission of MAO activity was consistent with either recessive or additive inheritance but not with dominant inheritance; the environmental hypothesis was strongly rejected. No effect of genotype on probability of illness was observed suggesting no relationship between the particular major locus tested and schizophrenia. The implications for genetic research in schizophrenia were discussed.

The Genain Quadruplets 25 years later: a diagnostic and biochemical followup

A biological and clinical followup of the Genain Quadruplets was initiated as a multilaboratory collaborative effort at the National Institute of Mental Health (NIMH). The quadruplets are 51-year-old monozygotic women previously studied with a battery of psychological and physiological tests 25 years ago at the NIMH. The present article (the first of a series of three) details the clinical history and course of the schizophrenic illness in each of the quadruplets and describes the biochemical measures determined. The findings of elevated urinary phenylethylamine excretion, decreased plasma dopamine-beta-hydroxylase activity, and increased alpha-adrenergic receptor concentrations in all quadruplets warrant further genetic studies.

Personality traits related to monoamine oxidase activity in platelets

Platelet monoamine oxidase (MAO) activity and intellectual level were examined in a large series of 1,129 18-year-old boys, selected from the general population. Personality traits were determined by means of selected subscales from several personality inventories such as the Zuckerman Sensation Seeking Scale, the Eysenck Personality Inventory, and the Karolinska Hospital Personality Inventory. Information was also gathered concerning alcohol consumption habits, signs of alcohol dependence, and use and abuse of tobacco, cannabis, glue, opiates, and amphetamine. Low MAO subjects were found to be more sensation seeking and to have higher scores on impulsivity and monotony avoidance. They also had higher use of tobacco and alcohol, showed more signs of possible alcohol dependence, and showed more drug abuse. When low MAO subjects were subdivided according to intellectual level, low MAO subjects with high intellectual level were found to have higher psychological functioning as judged by a psychologist after a clinical interview. Low MAO subjects with low intellectual level were found to have more use and abuse of alcohol and drugs, i.e., less accepted forms of sensation seeking, and they had a significantly lower level of psychological functioning. This subgroup seems to be the real "high risk" group that according to the high risk paradigm could be expected to show more alcohol abuse and higher tendencies to suicidal behavior.

Genetics of platelet MAO activity in discordant schizophrenic and normal twins

Platelet monoamine oxidase (MAO) activity was compared in four age and sex-matched groups: monozygotic (MZ) twins discordant for schizophrenia, normal MZ twins, normal dizygotic (DZ) twins and unrelated individuals. Among the twin groups, schizophrenic and normal there was a remarkably consistent degree of genetic control amounting to 70-80 per cent of the variation in activity. The mean platelet MAO activity of the schizophrenic twins was significantly lower than that of controls, but not than that of their psychiatrically well, neuroleptic-free cotwins; indeed the correlation for the MZ twins discordant for schizophrenia was almost exactly the same as that for the normal MZs. Thus, lower platelet MAO activity in schizophrenia, where it is found, is genetically modulated and not the result of the illness or its treatment.

A commingling analysis of platelet monoamine oxidase activity

The distribution of platelet monoamine oxidase (MAO) activity is examined in a large cohort of 18-year-olds from a college setting. A mixture of three distributions is needed to describe the data, even when a power transformation is used to remove skewness in the distribution. This is compatible with MAO activity being controlled by a single major locus with a gene frequency of 0.02 for high-MAO activity. Accordingly, it is unlikely that such a locus could serve as a genetic marker for a disorder which is associated with low activity. However, this finding does not rule out the possibility that MAO activity is an associated risk factor in disease.

Neuroleptic drug effect on platelet monoamine oxidase and plasma amine oxidase in schizophrenia

Activity levels of platelet monoamine oxidase (MAO) and plasma amine oxidase (PAO) were determined in eight chronic schizophrenic patients who had been treated with neuroleptic drugs for 3 months. The mean reduction in platelet MAO activity was 18.6%. The extent of decrease was statistically significant. The reduction in enzyme activity was unrelated to serum iron levels. PAO activity was unaltered. The implications for schizophrenia research are discussed.

Platelet MAO activity and family history of schizophrenia

Platelet monoamine oxidase (MAO) activity was studied in 50 drug-free schizophrenics divided into groups according to whether they had at least two first-degree relatives with schizophrenia (n = 6), only one first-degree relative with schizophrenia (n = 8), or no family history of schizophrenia (n = 36). Similar determination was made in 56 age-matched normals. There were no differences in the platelet MAO activity between any of the groups of schizophrenics or the normals. The results are discussed in light of previous studies of platelet MAO activity in schizophrenics with and without a family history of schizophrenia.

Platelet monoamine oxidase activity and behavioral response to pharmacotherapy in psychiatric patients

Platelet monoamine oxidase (MAO) levels were determined for drug-free psychiatric inpatients who were subsequently treated with neuroleptics, tricyclics, or lithium. Weekly, time-sampled recordings of specific behaviors were also made during both drug-free and medication periods. Significant correlations were obtained between MAO levels and changes in behavior scores subsequent to drug administration. For six of the seven recorded behaviors, correlations for patients treated with lithium vs. tricyclics were in the opposite direction. The results suggest that MAO levels, measured during a drug-free period, can predict some of the behavioral responses to antidepressant medications.

An overview of the genetics of psychopathology

The suggestion that psychopathologies are in part mediated by aberrant catecholamine metabolism has resulted in one of the more rapidly growing areas of pharmacogenetics. Collectively, the studies conducted to date indicate that psychopathological conditions have multiple causes which cannot be related to single genetic or biochemical deficits. However, through multidisciplinary research integrating behavioral, genetic, and biochemical approaches, a great deal of insight may be gained concerning the causes of psychopathological disorders and the use of drug therapy to modify the course of these illnesses.

Human platelet monoamine oxidase activity in health and disease: a review

The most readily available source of monoamine oxidase in man is the platelet, although only the B form of the enzyme is represented in this site. Platelet activity is higher in women than in men. The enzyme activity is generally stable and is partly under genetic control. There is some evidence that individuals with low activity have a higher psychiatric morbidity than those with high activity. Despite some negative studies, the consensus of publication dealing with schizophrenia, migraine, and alcoholism find that mean platelet monoamine oxidase activity in the patient group is lower than in the controls. Values are raised in unipolar depression. Technical differences, or patient or control group heterogeneity, might well account for the absence of unanimity in the literature. A considerable degree of overlap between patient and control values, whatever the clinical diagnosis, appears to be the standard finding. Apart from these neuropsychiatric disturbances, platelet monoamine oxidase activity is raised in megaloblastic anaemia and reduced in iron deficiency anaemia. Although altered enzyme activity values may be linked to abnormal platelet populations in some of the haematological disorders discussed, in general the causes of abnormal platelet monoamine oxidase activity are unknown.

A probable neuroleptic effect on platelet monoamine oxidase in chronic schizophrenic patients

Platelet monoamine oxidase activity (MAO) was studied serially over time in 16 chronic schizophrenic patients when medication free and then when medicated. Thirteen of the 16 patients had significant decreases in platelet MAO activity following neuroleptic drug treatment. The change in MAO activity was found to be correlated with response to treatment and to dose of medication.

Platelet monoamine oxidase activity in sensation seekers

Personality traits, as assessed by personality inventories, and platelet monoamine oxidase activities have been compared in the following two groups of normal subjects: (1) subjects who either have mountaineering as an active hobby or an interest in mountaineering and (2) subjects not interested in mountaineering. The group of subjects interested in mountaineering were found to be sensation seekers, as assessed by the Zuckerman Sensation Seeking Scale, and to have significantly lower platelet monoamine oxidase activities.

Reduced platelet MAO activity and vulnerability to psychiatric disorders

Platelet monoamine oxidase (MAO) is a genetically controlled mitochondrial enzyme that metabolizes amines in the brain by deamination. We investigated the relationship between MAO activity and the presence or absence of psychopathology by determining MAO activity and the psychiatric diagnosis in 61 first-degree relatives of 31 patients with bipolar (manic-depressive) illness. Relatives who themselves were diagnosed as having bipolar I illness or alcoholism had a significantly lower mean MAO activity level than did other relatives or 255 normal individuals. These findings indicate that a relationship exists within pedigrees between MAO activity and psychiatric disorders. Reduced MAO activity may play a role in vulnerability to some types of psychopathology.

Personality correlates of platelet monoamine oxidase activity anbd red cell lithium transport

Platelet monoamine oxidase (MAO) activity and the ratio of red cell to plasma lithium concentrations (Li ratio) may be important in the pathophysiology of, and genetic vulnerability to, some psychiatric disorders. By using the Clinical Analysis Questionnaire, we assessed personality correlates of MAO activity and the Li ratio in vitro in a sample of psychiatrically normal adult women. We found that there were correlates of each variable, and a unique constellation of personality traits when the two variables were considered simultaneously.