Reduced Smell Activity May Point To Schizophrenia Predisposition
Several years ago, Lili Kopala, M.D., a psychiatrist with Dalhousie University in Halifax, Nova Scotia, Canada, and her colleagues examined smell acuity in identical twins discordant for schizophrenia. The twins with schizophrenia had considerable olfaction impairment compared with healthy controls, but the twins without schizophrenia had some impairment as well. The unaffected twins’ performance fell midway between that of the affected twins and that of the healthy controls.
Fifty-eight percent of patients with schizophrenia, 34 percent of nonschizophrenia subjects from families with schizophrenia, and 9 percent of healthy controls had senses of smell in the impaired range. “Impaired” was defined as a score on the University of Pennsylvania Smell Identification Test of less than 34 of 40 for men and less than 35 of 40 for women. (Source: Lili Kopala, M.D., et al., Dalhousie University, Halifax, Nova Scotia)
This finding made Kopala and her coworkers wonder whether smell impairment might indicate a genetic susceptibility to schizophrenia in persons coming from families with a genetic predisposition to the disease. So they decided to test their hypothesis in another study.
The results, reported in the August American Journal of Psychiatry, confirm their hypothesis, Kopala and her colleagues believe.
Kopala and her coworkers gave a smell identification test to three groups of subjects younger than age 65. The first group consisted of 19 individuals with schizophrenia who came from families that had had various members with schizophrenia throughout the generations. In other words, it was clear that a strong genetic predisposition to schizophrenia was present in these families.
The second group consisted of 27 persons who also came from these families but who did not have schizophrenia. These individuals presumably had some genetic predisposition to schizophrenia as well, but had not developed schizophrenia.
A third group consisted of 43 healthy volunteers who were matched for age and gender to each schizophrenia and nonschizophrenia subject; an adequate match for three subjects could not be found.
The researchers then compared olfactory test results among the three groups. As they expected, subjects with schizophrenia performed worst on the test, healthy controls best, and subjects without schizophrenia but presumably with some genetic vulnerability to the disease in-between. Specifically, 58 percent of schizophrenia patients, 34 percent of nonschizophrenia subjects, and nine percent of healthy controls performed in the impaired range (see chart).
Thus, “impaired olfactory deficits may aggregate in families with schizophrenia and may be indicative of a genetic predisposition to psychosis,” Kopala and her colleagues conclude.
The report, “Impaired Olfactory Identification in Relatives of Patients with Familial Schizophrenia,” is posted on the journal’s Web site at ajp.psychiatryonline.org under the August issue.▪ AM J PSYCHIATRY20011581286
