Neurological soft signs show familial association in schizophrenia
MedWire News: Neurological soft signs are more common in schizophrenia patients and unaffected first-degree relatives than in people without a family history of the condition, a systematic review and meta-analysis of published studies show.
Neurological soft signs, which are common in schizophrenia patients, "are subtle but observable impairments in motor and sensory functions that are not localized to a specific area of the brain," explain Kishen Neelam (University of Manchester, UK) and team.
They add: "It has been established… that neurological soft signs in schizophrenia meet two criteria for an endophenotype: association with illness (because they occur much more frequently in people with schizophrenia than in controls) and state independence (because they are present whether or not the illness is active)."
To investigate whether neurological soft signs also meet a further criterion for an endophenotype, that of familial association, the team searched the literature for relevant published studies that compared levels of such impairments in schizophrenia patients, their first-degree relatives, and mentally healthy controls without a family history of schizophrenia.
In total, seven studies, involving 58 people with schizophrenia or schizophrenia-like disorders, 471 first-degree relatives, and 524 controls, met criteria for inclusion in the meta-analysis.
Soft signs were evaluated using the Neurological Evaluation Scale in three studies, the Standardised Neurological Examination in two studies, and the Condensed Neurological Examination in two studies.
Examination of the pooled data revealed that neurological soft signs were significantly more common in schizophrenia patients than in their first-degree relatives, at standardised mean difference (SMD) of 0.92, and significantly more common in first-degree relatives than controls, at an SMD of 1.24.
A sensitivity analysis that excluded data from two studies in which there was an age gap greater than 10 years between schizophrenia patients and their relatives, and excluded unblinded studies, did not significantly alter the findings, the researchers note.
Neelam and team conclude in the journal BMC Psychiatry: "Neurological soft signs show a pattern of familial association in schizophrenia that is compatible with the status of an endophenotype for the disorder."
However, they add: "There is a need for more studies using a consensual rating tool and homogeneous sample to establish that neurological soft signs are an endophenotype of schizophrenia.
"Prospective diagnostic studies are required to establish how far the identification of soft signs in at risk patients can augment the predictive power of established psychopathological tests."
By Mark Cowen