Eva Grof

Mapping susceptibility genes for bipolar disorder: a pharmacogenetic approach based on excellent response to lithium

Genetic mapping studies in bipolar disorder (BD) have been hampered by the unclear boundaries of the phenotypic spectrum, and possibly, by the complexity of the underlying genetic mechanisms, and heterogeneity. Among the suggested approaches to circumvent these problems, a pharmacogenetic strategy has been increasingly proposed. Several studies have indicated that patients with BD who respond well to lithium prophylaxis constitute a biologically distinct subgroup. In this study we have conducted a complete genome scan using 378 markers spaced at an average distance of 10 cM in 31 families ascertained through excellent lithium responders. Response to lithium was evaluated prospectively with an average follow-up of 12 years. Evidence for linkage was found with a locus on chromosome 15q14 (ACTC, lod score = 3.46, locus-specific P-value = 0.000014) and suggestive results were observed for another marker on chromosome 7q11.2 (D7S1816, lod score = 2.68, locus-specific P-value = 0.00011). Other interesting findings were obtained with markers on chromosomes 6 and 22, namely D6S1050 (lod score = 2.0, locus-specific P-value = 0.00004) and D22S420 (lod score = 1.91). Nonparametric linkage analysis provided additional support for the role of these loci. Further analyses of these results suggested that the locus on chromosome 15q14 may be implicated in the etiology of BD, whereas the 7q11.2 locus may be relevant for lithium response. In conclusion, our results provide original evidence suggesting that loci on 15q14 and 7q11.2 may be implicated in the pathogenesis of BD responsive to lithium.

Excess cardiovascular and suicide mortality of affective disorders may be reduced by lithium prophylaxis

The mortality of patients suffering from affective disorders is much higher than that of the general population; this excess is due to both suicides and cardiovascular disease. During long-term lithium treatment, the overall mortality has not been found to differ significantly from that of the general population but the question remains whether this lowering, if it is in fact caused by lithium, is due to a reduction in suicide frequency or cardiovascular mortality, or both. We analysed data from 827 previously studied patients and used a procedure that estimated both overall mortality and cause-specific mortalities by single-case analysis. For overall mortality, the ratio of observed deaths (among the patients) to expected deaths (in the general population) was 1.14, which is not significantly different from 1.0; this was also found in our previous analysis. In the whole patient group, comprising 5600 patient years under lithium treatment, seven suicides were observed and 1.3 expected, resulting in a standard mortality ratio of 5.22; this is significantly > 1.0, but markedly lower than that found in patients with affective disorders not given lithium. Cardiovascular mortality was not found to be higher in our patients than in the general population. In view of the fact that a placebo-controlled mortality study under long-term conditions is neither ethically nor practically feasible, our findings cannot prove definitively that long-term lithium treatment counteracts factors responsible for the excess suicide and cardiovascular mortality of affective disorders. However, our observations are compatible with such a notion.

The effect of long-term lithium treatment on the mortality of patients with manic-depressive and schizoaffective illness*

Clinical research centers in Aarhus, Berlin, Hamilton and Vienna collected mortality data for 827 manic‐depressive and schizoaffective patients given lithium treatment for more than 6 months. The average duration of the treatment was 81 months and the total time on lithium 5600 patient‐years. For each patient, the mortality risk was calculated by entering the appropriate national life tables for the general population. The number of observed deaths was 44; the number of expected deaths was 49.7. The standardized mortality ratio, 0.89, did not differ significantly from 1.0. The mortality of manic‐depressive patients is 2–3 times that of the general population. Our data show that the mortality of manic‐depressive and schizoaffective patients given long‐term lithium treatment does not differ significantly from that of the general population.

Evidence for a role of phospholipase C-γ1 in the pathogenesis of bipolar disorder

Several studies have indicated that patients with bipolar disorder (BD) who respond well to lithium prophylaxis constitute a biologically distinct subgroup. Lithium is thought to stablize mood by acting at the phosphoinositide cycle. We have investigated a polymorphism located in the gene (PLCG1) that codes for a γ-1 isozyme of phospholipase (PLC), an enzyme that plays an important role in the phosphoinositide second messenger system. A population-based association study and a family-based linkage study were carried out on patients who were considered excellent responders to lithium prophylaxis. Response to lithium was evaluated prospectively with an average follow-up of 14.4 ± 6.8 years. The PLCG1 polymorphism was investigated in 136 excellent lithium responders and 163 controls. In addition, the segregation of this marker was studied in 32 families ascertained through lithium-responsive bipolar probands. The allele distributions between lithium-responsive bipolar patients and controls were different, with a higher frequency of one of the PLCG1 polymorphisms in patients (χ2 = 8.09; empirical P = 0.033). This polymorphism, however, confers only a small risk (OR = 1.88, CI 1.19–3.00). Linkage studies with the same marker yielded modest support for the involvement of this gene in the pathogenesis of BD when unilineal families were considered (Max LOD = 1.45; empirical P = 0.004), but not in the whole sample. Our results provide preliminary evidence that a PLC isozyme may confer susceptibility to bipolar disorder, probably accounting for a fraction of the total genetic variance. Whether this polymorphism is implicated in the pathogenesis of BD or in the mechanism of lithium response remains to be determined.

Mortality during initial and during later lithium treatment : a collaborative study by the International Group for the Study of lithium-treated patients

We have previously shown that the mortality of patients with recurrent affective disorders in long‐term lithium treatment is not higher than that of the general population. In the present study on 471 patients from Denmark and Germany, we examined mortality during the initial year of lithium treatment and during later lithium treatment. During initial lithium treatment, the total mortality was twice as high as in the general population (difference not significant) and the mortality due to suicide 16 times higher. During later lithium treatment, the mortality rates did not differ from those in the general population. Our results indicate that patients with frequent, often severe recurrences, those chosen for prophylactic lithium treatment, are at risk of high mortality, which then diminishes as the prophylactic action of the treatment takes effect.

The cortisol awakening response in bipolar illness: a pilot study.

Objective: A growing body of data suggests that a significantly enhanced salivary cortisol response to waking may indicate an enduring tendency to abnormal cortisol regulation. Our objective was to apply the response test to a population already known to have long-term hypothalamo-pituitary-adrenocortical (HPA) axis dysregulation. We hypothesized that the free cortisol response to waking, believed to be genetically influenced, would be elevated in a significant percentage of cases, regardless of the afternoon Dexamethasone Suppression Test (DST) value. Method: Using the free cortisol response to waking and the short daytime profile, we tested 18 clinically stable, lithium-responsive subjects from our long-term naturalistic follow-up of monthly DSTs. These tests include salivary testing every 15 minutes during the first hour of waking, followed by samples taken at 3:00 PM and 8:00 PM. Results: While clinically stable on lithium prophylaxis, patients with bipolar disorder (BD) showed a significantly enhanced salivary cortisol response to waking, compared with control subjects (P < 0.03). Cortisol levels 30 minutes after waking significantly exceeded those in the large normative data provided in the literature (P < 0.001). Conclusions: Our observations support the hypothesis that the free cortisol response to waking can reflect relatively enduring HPA dysregulation, even when lithium-responsive BD patients are clinically well and their DSTs are normal. Because the test is easy to administer, the free cortisol response to waking may hold promise as a marker in studies of high-risk families predisposed to, or at risk for, mood disorders.

Mode of inheritance in families of patients with lithium-responsive affective disorders

A better understanding of the role of genetic factors in affective disorders is likely to result from investigating more homogeneous populations. To achieve this goal, we have systematically studied patients who are excellent responders to long‐term lithium treatment and their relatives. In the families of 71 such probands, we have analyzed the mode of inheritance by comparing the observed morbidity risks with the risks expected under different genetic models. The results demonstrate major‐gene effects in the transmission of primary affective disorders; the polygenic model with sex‐specific thresholds could be rejected. Discrimination between the autosomal and X‐chromosome models was not possible, but the autosomal recessive model predicts more realistic, gender‐specific frequencies of affective disorders in the general population. These results suggest that autosomal recessive inheritance deserves serious consideration in molecular genetic investigations.

Lithium responsive bipolar disorder, unilineality, and chromosome 18: A linkage study

Over the last three years several studies have investigated the hypothesis of linkage between bipolar disorder and markers on chromosome 18. Although independent groups have reported positive results, it is still not clear how these should be interpreted, as linkage spans a considerably large segment of the chromosome. In this study we have investigated linkage with chromosome 18 markers in 19 families of lithium-responsive bipolar patients, as a way to select a more homogeneous population. In addition, we have investigated whether there is evidence of a parent-of-origin effect as suggested by previous studies. Eleven markers spanning the whole chromosome were typed and linkage analysis was carried out using parametric and nonparametric methods. Analysis of the whole sample provided nonsignificant linkage results. However, when the sample included only unilineal families, and was further stratified according to parental origin, two chromosomal regions provided modestly positive lod scores. Maximum lod scores of 1.04 (P = 0.001) at D18S53 and 0.87 (P = 0.045) at D18S61 were observed for maternal and paternal pedigrees, respectively. Nonparametric analysis yielded similar results. In conclusion, our results are congruent with previous reports that suggest an advantage of unilineal pedigrees in linkage analysis of bipolar disorder and cannot rule out a parent-of-origin effect in this genomic region.

Lithium-responsive affective disorders: no association with the tyrosine hydroxylase gene.

Family, adoption, and twin studies have demonstrated the involvement of genetic factors in the etiology of major affective disorders. In an attempt to identify the involved genes, several linkage and association studies have focused on the gene coding for tyrosine hydroxylase, the rate-limiting enzyme in catecholamine synthesis. The discrepant results to date could be explained by etiological heterogeneity, which may be substantially reduced by selecting patients according to lithium response. Therefore, we investigated 54 patients who had shown definite long-term response to lithium monotherapy in spite of a high risk of recurrence as indicated by the previous clinical course. All the subjects suffered from major affective disorder by Research Diagnostic Criteria (48 bipolar, 6 recurrent unipolar). They were compared to 94 population controls of similar ethnic background to test for association with a penta-allelic microsatellite marker found within the tyrosine hydroxylase gene. No significant differences in allele and genotype frequencies were observed between the two groups, providing further evidence against a major role for the tyrosine hydroxylase gene in the etiology of major affective disorders.

Patterns of DST positivity in remitted affective disorders.

BACKGROUND While the Dexamethasone Suppression Test (DST) has been extensively used in cross-sectional observations of patients with major affective disorders, studies have tended to ignore the longitudinal application of the DST in patients stabilized on long-term prophylactic medication. METHODS Monthly DSTs were performed on 19 patients, 16 with bipolar disorder and 3 with recurrent major depression. All cases had an excellent response to lithium treatment, and family history positive for bipolar disorder. The average duration of observation was 4 years. RESULTS All patients remained clinically stable throughout the period of observation. Eleven patients showed intermittent DST positivity ranging from 10% to 60% of tests, and 2 patients exhibited no positivity. Six patients had fewer than 10% positive DSTs. Females showed significantly higher positivity than males. The frequency of positivity did not correlate with current age, age of illness onset, duration of illness, duration of lithium treatment, or season. The risk of primary affective disorders in first-degree relatives was also unrelated to the frequency of positivity. CONCLUSIONS While the highly selected and small sample population limits generalizability, our observations suggest that clinically sufficient lithium prophylaxis does not automatically prevent intermittent HPA dysregulation. We hope that a better understanding of this phenomenon will offer new approaches to the long-term management of mood disorders.