Leon Karp

A Highly Significant Association between a COMT Haplotype and Schizophrenia

Several lines of evidence have placed the catechol-O-methyltransferase (COMT) gene in the limelight as a candidate gene for schizophrenia. One of these is its biochemical function in metabolism of catecholamine neurotransmitters; another is the microdeletion, on chromosome 22q11, that includes the COMT gene and causes velocardiofacial syndrome, a syndrome associated with a high rate of psychosis, particularly schizophrenia. The interest in the COMT gene as a candidate risk factor for schizophrenia has led to numerous linkage and association analyses. These, however, have failed to produce any conclusive result. Here we report an efficient approach to gene discovery. The approach consists of (i) a large sample size-to our knowledge, the present study is the largest case-control study performed to date in schizophrenia; (ii) the use of Ashkenazi Jews, a well defined homogeneous population; and (iii) a stepwise procedure in which several single nucleotide polymorphisms (SNPs) are scanned in DNA pools, followed by individual genotyping and haplotype analysis of the relevant SNPs. We found a highly significant association between schizophrenia and a COMT haplotype (P=9.5x10-8). The approach presented can be widely implemented for the genetic dissection of other common diseases.

COMT: A common susceptibility gene in bipolar disorder and schizophrenia

A variety of psychiatric illnesses, including schizophrenia and bipolar disorder, have been reported in patients with microdeletion on chromosome 22q11—a region which includes the catechol‐O‐methyltransferase (COMT) gene. The variety of psychiatric manifestations in patients with the 22q11 microdeletion and the role of COMT in the degradation of catecholamine neurotransmitters may thus suggest a general involvement of the COMT gene in psychiatric diseases. We have previously reported on a significant association between a COMT haplotype and schizophrenia. In this study, we attempt to test for association between bipolar disorder and the polymorphisms implicated in schizophrenia. The association between COMT and bipolar disorder was tested by examining the allele and haplotype found to be associated with schizophrenia. A significant association between bipolar disorder and COMT polymorphisms was found. The estimated relative risk is greater in women, a result consistent with our previous findings in schizophrenia. We suggest that polymorphisms in the COMT gene may influence susceptibility to both diseases—and probably also a wider range of behavioral traits.

Cytokine production in drug-free and neuroleptic-treated schizophrenic patients

A line of evidence indicates changes of the immune system in schizophrenic patients. We investigated the production of cytokines by peripheral blood mononuclear cells (PBMCs) in drug-free and neuroleptic-treated schizophrenic patients compared to healthy, normal controls. A significant reduction in interleukin (IL)-2 production was detected in untreated schizophrenic patients (-59.6%; p < .05) as well as in IL-3-like activity (IL-3-LA) production (-27.4%; p < .05) in treated patients compared to controls. No alteration was observed in IL-1 beta production. It seems that schizophrenia is associated with diminished IL-2 production, while neuroleptic treatment interferes with the capacity of immunocompetent cells to synthesize and/or release Il-3-LA. The alteration in cytokine production did not correlate with either the severity of the disorder or the serum prolactin levels.

Altered platelet peripheral-type benzodiazepine receptor in posttraumatic stress disorder

Peripheral-type benzodiazephine receptors (PBR) are involved in steroidogenesis and are sensitive to stress. Reduced platelet PBR density has been demonstrated in generalized anxiety disorder (GAD), but not in obsessive-compulsive disorder (OCD). We extended this observation to another anxiety disorder, namely, posttraumatic stress disorder (PTSD). Eighteen post-Persian Gulf War PTSD patients and 17 age- and sex-matched controls were included in the study. All subjects were evaluated using the Structured Clinical Interview for DSM-III-R-Patient Version. The severity of symptoms was assessed using the DSM-III-R scale for PTSD, the Impact of Event Scale, the Beck Depression Inventory, and the State-Trait Anxiety Inventory. [3H]PK 11195 was used to label platelet PBR. All psychological parameters (except trait anxiety) were higher in PTSD patients compared to controls. Decreased platelet PBR density (−62%; p <. 001) was observed in the PTSD patients compared to controls. The reduction in PBR observed in PTSD patients was in accordance with the findings in GAD patients, but differed from those obtained in OCD patients. It is possible that the receptoral downregulation is an adaptive response aimed at preventing chronic overproduction of glucocorticoids in hyperarousal states.

Decreased peripheral benzodiazepine binding sites in platelets of neuroleptic-treated schizophrenics

A decrease of 30% was observed in the density of peripheral-type benzodiazepine binding sites in platelets of nine schizophrenics maintained on chronic neuroleptic treatment as compared to platelets of six untreated schizophrenics and 15 healthy volunteers. The equilibrium dissociation constant for binding by [3H]PK 11195, which is a ligand specific for peripheral benzodiazepine binding sites, was similar in all three groups. The relevance of the reduction in peripheral-type benzodiazepine binding sites to central or peripheral side-effects induced by long-term neuroleptic treatment merits further investigation.

Examination stress, platelet peripheral benzodiazepine binding sites, and plasma hormone levels

The maximal binding capacity (Bmax) and the equilibrium dissociation constant (KD) values for [3H]PK 11195 binding to peripheral benzodiazepine binding sites were measured in the platelets of subjects immediately after examination stress and 10 days later, as well as in unstressed controls. Increased (52%; p less than 0.05) Bmax, but unaltered KD, values were observed immediately after the stress as compared to the controls. Ten days after the stress, a slight decrease (15%) in the number of peripheral benzodiazepine binding sites was observed, but their values remained higher (29%) in comparison to unstressed controls. Levels of plasma stress hormones (cortisol, growth hormone, and prolactin) did not differ in the stressed subjects from those of the controls.

Cytokine production in anorexia nervosa.

The capacity of peripheral blood mononuclear cells (PBMCs) of anorexia nervosa (AN) patients to produce interleukin-1 (IL-1), interleukin-2 (IL-2), and interleukin-3-like activity (IL-3-LA) was studied. A significantly lower (-49%, p < 0.005) capacity to synthesize IL-2 and an almost significantly impaired ability (-35%, p = 0.058) to release IL-3-LA by PBMCs of AN patients was found, as compared with cells of the control group. IL-1 production, either spontaneous or after stimulation with lipopolysaccharide (LPS), did not differ significantly between AN patients and healthy subjects. The lessened capacity to produce IL-2 was accompanied by an enhanced stimulatory activity of the patient sera on the production of this cytokine by PBMCs of healthy subjects. It is therefore suggested that the serum of AN patients contains a stimulatory factor or factors for cytokine production that compensates for the lower production of cytokines by AN PBMCs. Such a compensatory mechanism may explain why AN patients do not have an higher susceptibility to infections.

Platelet peripheral-type benzodiazepine receptor in major depression

The peripheral-type benzodiazepine receptor (PBR) plays a major role in steroidogenesis. This receptor is sensitive to endocrine changes and stress. Antidepressants have been demonstrated to modulate adrenal and hepatic PBR in rats. To evaluate the relationship between depression and PBR, we measured platelet PBR in untreated depressed patients (n = 14) in comparison to normal controls (n = 13). Platelet PBR density (Bmax) and the dissociation constant (kd) of the receptor did not differ in the patients when compared with normal controls. Furthermore, no correlation was found between Bmax values and the severity of the depression (as measured by the Hamilton Depression Rating Scale and Beck Depression Inventory) as well as with the severity of the anxiety (as measured by the Hamilton Anxiety Rating Scale). It seems that major depression, in contrast to stress and some anxiety disorders, is not associated with alteration of PBR.

Platelet peripheral benzodiazepine receptors in repeated stress.

[3H]PK 11195 binding to platelet membranes and plasma stress hormones were studied in soldiers at the beginning of a parachute training course, following 6 days of preparatory exercises, and after the fourth actual parachute jump. A slight reduction (15%; NS) in the number of peripheral benzodiazepine receptors (PBR) was detected at the end of the exercise period, prior to the first jump. Reduced (26%; P less than 0.05) density of PBR was observed immediately after the repeated actual jumps. Equilibrium dissociation constants were not affected by the stressful situation. Plasma cortisol and prolactin levels remained unaltered during the entire study period.

Peripheral-type benzodiazepine-binding sites in platelets of schizophrenics with and without tardive dyskinesia

The density of peripheral-type benzodiazepine (BZ)-binding sites was studied in platelets of 10 medicated chronic schizophrenics with tardive dyskinesia (TD), 10 medicated chronic schizophrenics without TD, 7 drug-free schizophrenics, and 10 normal controls. The age range of the study population was 36-60 years. Age and sex distribution were similar in all 4 groups. The unmedicated schizophrenics did not differ in their maximal binding capacity from the healthy controls. A significant decrease in the density of peripheral-type BZ-binding sites in platelets was observed in treated schizophrenics both with and without TD in comparison to controls and untreated schizophrenics. The reduction in [3H]PK 11195 binding was more pronounced in TD patients (31.3% of controls) than in patients without TD (21.1% of controls). However, this parameter failed to discriminate statistically between TD and non-TD medicated schizophrenics.