Apolipoprotein E polymorphism is associated with susceptibility to schizophrenia among Saudis

Introduction: Apolipoprotein E (APOE) genotypes influence the phenotype of several neurodegenerative disorders including Alzheimer's and Parkinson disease and may affect schizophrenia pathogenesis. This study was undertaken to determine the association between APOE gene polymorphisms and schizophrenia in the Saudi population. Material and methods: APOE allele and genotype frequencies were studied in 380 Saudi subjects including schizophrenia patients and matched controls using polymerase chain reaction (PCR) and reverse-hybridization techniques. Results: The frequencies of the APOE allele epsilon 2 and genotypes epsilon 2/epsilon 3 and epsilon 2/epsilon 4 were significantly higher in the schizophrenia patients as compared to controls, suggesting that the epsilon 2 allele and its heterozygous genotypes may increase the susceptibility to schizophrenia. In contrast, the frequencies of the epsilon 3 allele and epsilon 3/epsilon 3 genotype were lower in patients as compared to controls, suggesting a protective effect of APOE epsilon 3 for schizophrenia. This study indicated that APOE epsilon 4 was differentially associated with schizophrenia depending on the symptoms as the frequency of the epsilon 4 allele was significantly higher in schizophrenia patients with positive symptoms. By contrast, no significant association between APOE epsilon 4 and schizophrenia patients with negative symptoms was observed. Genotypes epsilon 2/epsilon 2 and epsilon 4/epsilon 4 were absent in patients and controls. Moreover, the age of onset was significantly lower in patients with the APOE epsilon 2/epsilon 3 genotype. There was no significant difference in the frequencies of APOE alleles and genotypes between male and female schizophrenia patients. Conclusions: The results of this study clearly show that APOE alleles and genotypes are associated with risk of developing schizophrenia and early age of onset in Saudis.