Herman W Pretorius

Assessment of the frequency of the 22q11 deletion in Afrikaner schizophrenic patients.

A hemizygous deletion of the q11 band on chromosome 22 occurs in 1 of every 5,950 live births (0.017%). The deletion is mediated by low copy repeats (LCRs) flanking this locus. Presence of the deletion is associated with variable phenotypic expression, which can include distinctive facial dysmorphologies, congenital heart disease and learning disabilities. An unusually high percentage of individuals with this deletion (25–30%) have been described to develop schizophrenia or schizoaffective disorder. In previous studies, the prevalence of the 22q11 deletion in patients with schizophrenia was found to be approximately 2% in Caucasian adults and 6% in childhood‐onset cases. Both these frequencies represent a dramatic increase from the prevalence of the deletion in the general population. In this study, we investigate the occurrence of the 22q11 deletion in an independent sample of schizophrenic patients of Afrikaner origin. We first ascertained a sample of 85 patients who meet full diagnostic criteria for schizophrenia for presence of two or more of the clinical features associated with presence of the 22q11 deletion. A group of six patients (7%) met these criteria. This group was subjected to fluorescent in situ hybridization (FISH) and presence of the 22q11 deletion was confirmed for two subjects. Our study therefore confirms the previously reported rate of 2% frequency of the 22q11 deletion in adult schizophrenic patients and provides a two‐stage screening protocol to identify these patients.

Phenotypic characterization and genealogical tracing in an Afrikaner schizophrenia database.

Founder populations hold tremendous promise for mapping genes for complex traits, as they offer less genetic and environmental heterogeneity and greater potential for genealogical research. Not all founder populations are equally valuable, however. The Afrikaner population meets several criteria that make it an ideal population for mapping complex traits, including founding by a small number of initial founders that likely allowed for a relatively restricted set of mutations and a large current population size that allows identification of a sufficient number of cases. Here, we examine the potential to conduct genealogical research in this population and present initial results indicating that accurate genealogical tracing for up to 17 generations is feasible. We also examine the clinical similarities of schizophrenia cases diagnosed in South Africa and those diagnosed in other, heterogeneous populations, specifically the US. We find that, with regard to basic sample descriptors and cardinal symptoms of disease, the two populations are equivalent. It is, therefore, likely that results from our genetic study of schizophrenia will be applicable to other populations. Based on the results presented here, the history and current size of the population, as well as our previous analysis addressing the extent of background linkage disequilibrium (LD) in the Afrikaners, we conclude that the Afrikaner population is likely an appropriate founder population to map genes for schizophrenia using both linkage and LD approaches.

A comparison study of early non-psychotic deviant behavior in Afrikaner and US patients with schizophrenia or schizoaffective disorder

In a previous study early non-psychotic deviant behaviors in US adult schizophrenic patients recruited for a large-scale genetic study were examined (Psychiatry Research, 101, 101). Early deviance characterized a distinct subgroup of patients at rates that were consistent with earlier reports. In addition, specific early non-psychotic deviant behaviors were meaningfully associated with later disease outcomes. In the present study, we examined the demographic, syndrome course, symptom and early deviant behavior history of 109 Afrikaner probands who met criteria for DSM schizophrenia or schizoaffective disorder, and compared them to 109 age- and gender-matched US probands. Consistent with past findings, 68% of Afrikaner probands, as compared to 67% of age- and gender-matched US probands, reported one or more forms of early non-psychotic deviance, including poor socialization, extreme fears/chronic sadness, and/or attention/learning impairment. The remaining 32 and 33% of probands, respectively, were without behavioral deviance until the onset of schizophrenia or schizoaffective disorder. The frequency and distribution of individual deviant behaviors were strikingly consistent between the samples. However, logistic regression analyses revealed different patterns of associations between the early deviant behaviors manifested and disease outcome. Afrikaner participants with early fears/chronic sadness were 3 times more likely to attempt suicide, while among US participants, this form of early deviance conferred 3.5 times more risk for later schizoaffective disorder, and 3 times greater likelihood of later sensory (tactile and/or olfactory) hallucinations. Afrikaner participants with attention/learning impairment were 2.5 times more likely to experience later auditory hallucinations, while US participants with these early difficulties were 3 times more likely to experience thought disorder. We concluded that early non-psychotic childhood deviance in this independently collected Afrikaner population distinguished a distinct subtype of patients and that the forms of early deviance manifested were meaningfully linked to later disease outcome. Possible reasons for the association pattern differences in these two populations are considered.

Clinical Characteristics of an Afrikaner Founder Population Recruited for a Schizophrenia Genetic Study

The clinical characteristics of an Afrikaner founder population sample recruited for a schizophrenia genetic study are described. Comparisons on several clinical characteristics between this sample and a U.S. sample of schizophrenia patients show that generalization of findings in a founder population to the population at large is applicable. The assessment of the frequency of the 22q11 deletion in Afrikaner schizophrenia patients is approximately 2%, similar to findings in a U.S. sample. Results of analysis of early non‐psychotic deviant behavior in subjects under the age of 10 years in the Afrikaner population broadly replicated findings in a U.S. sample. Approximately half of male schizophrenia patients and a quarter of female patients in the Afrikaner schizophrenia database used or abused cannabis. Male users of cannabis with severe early deviant behavior had the lowest mean age of criteria onset, namely 18.4 years. These findings confirm previous findings, indicating that early deviance is linked to later outcome of disease. The clinical characteristics and premorbid variables in 12 childhood‐onset Afrikaner schizophrenia patients thus far recruited in this study compare favorably with what is known about childhood‐onset schizophrenia in a U.S. sample. The prevalence of co‐morbid OCD/OCS in this Afrikaner schizophrenia founder sample was 13.2% which is in keeping with that of co‐morbid OCD in schizophrenia, estimated at 12.2% by the U.S. National Institute of Mental Health. These findings confirm that the clinical characteristics of a schizophrenia sample drawn from the Afrikaner founder population can be generalized to the schizophrenia population at large when compared to findings reported in the literature.