CAG nucleotide repeat profiles in persons with schizophrenia of schizoaffective disorders with and without tardive dyskinesia: Pilot study

Tardive dyskinesia (TD) is a drug-induced syndrome of involuntary movements often associated with neuroleptic treatment of psychiatric conditions. Huntington's disease (HD) and other neurological conditions are caused by CAG nucleotide repeat expansions in specific genes. We, therefore, explore the hypothesis that TD may be related to CAG repeat expansion by using the repeat expansion detection (RED) method as a measure of CAG content without knowledge of the location of the responsible gene. The number of CAG repeats ([CAG] _n) from persons with schizophrenia or schizoaffective disorders with (n = 10) and without (n = 9) TD are determined. A comparison of [CAG] _n in persons with (56.90 ± 23.45 repeats) and without (57.00 ± 19.35 repeats) TD was not statistically different. The total [CAG] _n was determined by combining [CAG]_n for both groups. The median of 45 repeats was used to divide the total into two groups (SG1 and SG2 with smaller and larger [CAG]_n fragments, respectively) and a means analysis of the two subgroups based on [CAG]_n demonstrated that SG1 (n = 10 samples at 45 repeats per sample, mean [CAG]_n = 45.00 ± 0.00) was significantly smaller than SG2 (n = 9, ranging from 48 to 120 repeats, mean = 70.22 ± 24.83; P < 0.005). Thus, this lends support to the idea of CAG repeat expansions in the study population. Results are encouraging that a larger population and a more structured subject selection process may yield more meaningful information about the relationship between CAG repeat expansion and TD.