Neurological soft signs were examined in a group of healthy volunteers selected according to their positive schizotypy score, as measured by the Unusual Experiences subscale from the O-LIFE25
and the LSHS.26
The high psychosis-prone individuals showed more soft signs overall and on the Other Soft Signs subscale. From an examination of the means for the remaining subscales from the NES, the group differences occurred in the predicted direction, although they did not reached significance. Using 2 separate regression models, the total from the NES and the Other Soft Signs subscales significantly predicted psychosis proneness group.
A number of studies have used the Neurological Evaluation Scale in samples of patients with schizophrenia; some produced results that support the data from the current study. Ismail et al.28
reported that patients with schizophrenia and their siblings scored higher than normal controls on the Soft Signs Total, as well as the Sensory Integration and Motor Functioning subscales. Additionally, patients with schizophrenia have been reported to score higher than at-risk patients, who in turn scored higher than controls on the Soft Signs Total, Sensory Integration, and Other Soft Signs.29
Arango et al.30
reported that the Other Soft Signs subscale was able to correctly classify a greater number of patients and controls to their true group than the other subscales from the NES. Taken together these previous studies and the current results suggest that the Other Soft Signs subscale may be particularly sensitive in identifying those with schizophrenia or a proneness to it.
Griffiths et al.18
suggested that the presence of soft signs in relatives increases with the potential genetic loading (ie, greater incidence of schizophrenia in a family increases the presence of soft signs). Furthermore, Gourion et al.31
reported that the Total Soft Signs score could be used to distinguish relatives who were thought to be carriers of the genetic vulnerability to schizophrenia from those who were not. This suggests that the presence of neurological soft signs may be indicative of being a “gene-carrier” for psychosis. It is not possible, on the information available, to determine whether the participants in the current study are gene-carriers for schizophrenia. However, a high score on a schizotypal personality questionnaire is considered a phenotypic marker for possible development of schizophrenia.eg,32,33
However, the results from Lawrie et al.29
may suggest that soft signs are not an indicator of genetic risk specifically for psychosis. Other causes of soft signs may be low birth weight34,35
and obstetric complications.36
Obstetric complications may be a more significant factor for males at risk for schizophrenia,37
or for leading to soft signs in those at genetic risk for developing schizophrenia.38
Additionally, childhood illnesses such as whooping cough, meningitis, and tuberculosis have been associated with soft signs in adulthood.39
At the very least, these studies suggest that the relationship between soft signs and schizophrenia is not a simple one, with many mediating variables being implicated.
Some clarification of the intermediate variables may result from examining the genes associated with soft signs. For example, Lautenschlager et al.40
reported that the neurological soft signs were associated with apolipoprotein E gene (which has been implicated in Alzheimer disease41
), age, and cognitive performance. With the increasing interest in the functional effects of single nucleotide polymorphisms, it would be beneficial to determine whether genes implicated in the dopamine and glutamate pathways confer risk for the presence of neurological soft signs.