A computer-simulation method is presented for determining and correcting for the effect of maximizing the lod score over disease definitions, penetrance values, and perhaps other model parameters. The method consists of simulating the complete analysis using marker genotypes randomly generated under the assumption of free recombination. It is applicable as a "post-treatment" to linkage analyses of any trait with an uncertain mode of inheritance and/or disease definition. When the method is applied to a linkage analysis of schizophrenia versus chromosome 5 markers, we find that, in this specific case, the P-value associated with a maximum lod score of 3 is equal to 0.0003. We also find that a lod score of 3.0 should be "deflated" by approximately 0.3 to 1 units, and, by tentative extrapolation, the observed lod score of 6.5 should be "deflated" by 0.7 to 1.5 units.
A cohort of 168 psychotic patients underwent computerised tomography (CT) during their first admission. Cortical atrophy was present in 40% of patients. The frequency of atrophy increased with age, but did not differ between patients with schizophrenia, schizoaffective disorder, bipolar disorder or psychotic depression. Other CT findings of note were present in 6.6% of patients, and included four infarctions, three arachnoid cysts, and one each of venous angioma, colloid cyst, cavum vergae and post-traumatic changes. The frequency of CT findings other than atrophy was increased in the psychotic depression group. The findings support the proposal of the onset of psychosis being an indication for CT.
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