Heritability estimates of spatial working memory and set-shifting in a healthy Chinese twin sample: A preliminary study.

Impairments in spatial working memory (SWM) and set-shifting abilities have both been consistently observed in individuals with schizophrenia and are considered to be potential endophenotypes of this illness. However, an endophenotype needs to fulfill a set of stringent criteria, including heritability. This study examined the heritability of these two functions in a healthy Chinese twin sample. Forty-five pairs of monozygotic (MZ) twins and 35 pairs of dizygotic (DZ) twins completed the SWM task and the Intra-Extra Dimensional Set-Shifting (IED) task of the Cambridge Neuropsychological Test Automated Battery (CANTAB). We found a moderate heritability for SWM, of which the familial/genetic factors accounted for 33% of the total variance. However, we failed to find any significant heritability for set-shifting ability, of which the specific environmental factor explained most of the variance (85%). The preliminary findings from this small healthy Chinese twin sample suggest that SWM is heritable, whereas the set-shifting ability may reflect "extra-genetic" influences.