Digit ratio (2D:4D) asymmetry and Schneiderian first rank symptoms: implications for cerebral lateralisation theories of schizophrenia.

Schneiderian first rank symptoms (FRS) in schizophrenia have been hypothesised to be secondary to aberrant cerebral lateralisation over the course of human evolution. The ratio of length of second digit to fourth digit (2D:4D) has been put forward as a potential indicator of cerebral lateralisation. This study examined 2D:4D and its asymmetry in antipsychotic-naïve schizophrenia patients (N=79) in comparison with healthy controls (N=75). Psychopathology was assessed using Scales for Assessment of Positive and Negative Symptoms. FRS assessment was performed as per established descriptions. The digit lengths (2D & 4D) were measured using a digital vernier caliper with good inter-rater reliability. Female schizophrenia patients showed significantly lower 2D:4D than female healthy controls. Mean 2D:4D asymmetry index was significantly lower in male schizophrenia patients than male healthy controls. FRS status had significant effect on left 2D:4D as well as 2D:4D asymmetry index, the patients with FRS having the lowest values. Our study findings support association between schneiderian FRS and low 2D:4D as well as low 2D:4D asymmetry index. Since 2D:4D is linked with limbic asymmetry, our study findings offer further support to the cerebral lateralisation theories of schizophrenia.