No Association between (AAT)n Repeat Polymorphisms in the Cannabinoid Receptor 1 Gene and Smooth Pursuit Eye Movement Abnormality in Korean Patients with Schizophrenia

ABSTRACT

OBJECTIVES: According to previous studies, the cannabinoid receptor 1 (CNR1) gene could be an important candidate gene for schizophrenia. Some studies have linked the (AAT)n trinucleotide repeat polymorphism in CNR1 gene with the risk of schizophrenia. Meanwhile, smooth pursuit eye movement (SPEM) has been regarded as one of the most consistent endophenotypes of schizophrenia. In this study, we investigated the association between the (AAT)n trinucleotide repeats in CNR1 gene and SPEM abnormality in Korean patients with schizophrenia. METHODS: We measured SPEM function in 167 Korean patients with schizophrenia (84 male, 83 female) and they were divided according to SPEM function into two groups, good and poor SPEM function groups. We also investigated allele frequencies of (AAT)n repeat polymorphisms on CNR1 gene in each group. A logistic regression analysis was performed to find the association between SPEM abnormality and the number of (AAT)n trinucleotide repeats. RESULTS: The natural logarithm value of signal/noise ratio (Ln S/N ratio) of the good SPEM function group was 4.34 ± 0.29 and that of the poor SPEM function group was 3.21 ± 0.70. In total, 7 types of trinucleotide repeats were identified, each containing 7, 10, 11, 12, 13, 14, and 15 repeats, respectively. In the patients with (AAT)₇ allele, the distributions of the good and poor SPEM function groups were 18 (11.1%) and 19 (11.0%) respectively. In the patients with (AAT)₁₀ allele, (AAT)₁₁ allele, (AAT)₁₂ allele, (AAT)₁₃ allele, (AAT)₁₄ allele and (AAT)₁₅ allele, the distributions of good and poor SPEM function groups were 13 (8.0%) and 12 (7.0%), 4 (2.5%) and 6 (3.5%), 31 (19.8%) and 35 (20.3%), 51 (31.5%) and 51 (29.7%), 36 (22.2%) and 45 (26.2%), 9 (5.6%) and 4 (2.3%) respectively. As the number of (AAT) n repeat increased, there was no aggravation of abnormality of SPEM function. CONCLUSIONS: There was no significant aggravation of SPEM abnormality along with the increase of number of (AAT)n trinucleotide repeats in the CNR1 gene in Korean patients with schizophrenia.