“…who was blind to zygosity and to the diagnostic status of the other co-twin. Variables selected for quantitative trait locus analysis consisted of 8 test indexes that discriminated affected from unaffected co-twins, degree of genetic loading for schizophrenia, or both, as previously described 27 : spatial working memory, 43 divided attention, 44 choice reaction time, 45 verbal learning and memory, 46 intrusions during verbal memory retrieval, 46 semantic clustering during verbal memory retrieval, 46 visuospatial learning and memory, 43 and motor speed. 47 All groups were within 1 SD of normal in terms of a composite average of the age-scaled standard scores on the vocabulary, similarities, block design, and digit symbol subtests of the Wechsler Adult Intelligence Test-Revised.…”