Abstract
The population with schizophrenia is characterised by a leftward shift in handedness-sinistrality. However, findings are inconsistent in chronic patients, and familial sinistrality (FS), defined as the presence of left-handed close relatives, might contribute to the discrepancies.
Therefore the aim of this study was to investigate the strength of manual lateralisation in patients with first episode schizophrenia, taking into account familial sinistrality. The Edinburgh Inventory (EI) allowed us to categorise 179 patients from the EUFEST study and 189 controls presenting "strong handedness'' (SH: EI absolute value between j81j and j100j) or "weak-handedness'' (WH: EI value between -80 and +80).
The nominal logistic regression did not show an FS effect, but a nearly significant interaction between illness and FS (p = .07). There were fewer participants without FS presenting SH among patients (99/151: 65.6%) than among controls (134/164: 81.7%, p = .001).
In contrast, the number of participants with FS presenting SH was similar between controls (68%) and patients (75%, p = .57). The presence of left-handed relatives (FS +) tended to reduce manual lateralisation, but only in controls.
This supports the notion that reduced manual lateralisation in schizophrenia is related to the illness rather than to familial left-handedness.