Risk of Population Extinction from Periodic and Abrupt Changes of Environment

A simulation model of a population having internal (genetic) structure is presented. The population is subject to selection pressure coming from the environment which is the same in the whole system but changes in time. Reproduction has a sexual character with recombination and mutation. Two cases are considered - oscillatory changes of the environment and abrupt ones (catastrophes). We show how the survival chance of a population depends on maximum allowed size of the population, the length of the genotypes characterising individuals, selection pressure and the characteristics of the climate changes, either their period of oscillations or the scale of the abrupt shift.Comment: 8 pages, 25 references, 10 figures; preliminary version to be submitted to Physica

Clozapine treatment for suicidality in schizophrenia: International Suicide Prevention Trial (InterSePT)

Background: Approximately 50% of patients with schizophrenia or schizoaffective disorder attempt suicide, and approximately 10% die of suicide. Study results suggest that clozapine therapy significantly reduces suicidal behavior in these patients. Methods: A multicenter, randomized, international, 2-year study comparing the risk for suicidal behavior in patients treated with clozapine vs olanzapine was conducted in 980 patients with schizophrenia or schizoaffective disorder, 26.8% of whom were refractory to previous treatment, who were considered at high risk for suicide because of previous suicide attempts or current suicidal ideation. To equalize clinical contact across treatments, all patients were seen weekly for 6 months and then biweekly for 18 months. Subsequent to randomization, unmasked clinicians at each site could make any interventions necessary to prevent the occurrence of suicide attempts. Suicidal behavior was assessed at each visit. Primary end points included suicide attempts (including those that led to death), hospitalizations to prevent suicide, and a rating of "much worsening of suicidality" from baseline. Masked raters, including an independent suicide monitoring board, determined when end point criteria were achieved. Results: Suicidal behavior was significantly less in patients treated with clozapine vs olanzapine (hazard ratio, 0.76; 95% confidence interval, 0.58-0.97; P = .03). Fewer clozapine-treated patients attempted suicide (34 vs 55; P = .03), required hospitalizations (82 vs 107; P = .05) or rescue interventions (118 vs 155; P = .01) to prevent suicide, or required concomitant treatment with antidepressants (221 vs 258; P = .01) or anxiolytics or soporifics (301 vs 331; P = .03). Overall, few of these high-risk patients died of suicide during the study (5 clozapine vs 3 olanzapine-treated patients; P = .73). Conclusions: Clozapine therapy demonstrated superiority to olanzapine therapy in preventing suicide attempts in patients with schizophrenia and schizoaffective disorder at high risk for suicide. Use of clozapine in this population should lead to a significant reduction in suicidal behavior