Tardive dyskinesia: Who gets it and why.

Tardive dyskinesia (TD) is a potentially permanent movement disorder resulting from chronic use of dopamine receptor blocking agents (DRBA). Identified risk factors include the type of antipsychotic agent, being greater for those of first generation antipsychotics (FGA), the duration of illness and cumulative dose of DRBA and advanced age. Female sex and African and Caucasian ethnicity are additional potential risk factors. Because only a subset of people taking DRBA's develops TD, genetics may play a role. Susceptibility gene candidates include those involved in DRBA metabolism and the targets or receptors of DRBA's. Although met with conflicting data, the following genes may be involved with TD development: the cytochrome P450 gene CYP2D6, involved with metabolism of most antipsychotics, Dopamine D2 and D3 receptor genes, serotonin 2A and 2C receptor genes, vesicular monoamine transporter 2 (VMAT 2) gene, involved with intracellular neurotransmitter packaging, and the manganese superoxide dismutase (MnSOD) gene, an antioxidant enzyme. Heparan sulfate proteoglycan 2 (HSPG 2) gene is another potential gene involved with development of TD. The pathogenesis of TD is unknown, however there are three main theories proposed: dopamine receptor supersensitivity resulting from chronic dopamine receptor blockade, oxidative stress and maladaptive synaptic plasticity each of which is discussed further in this article. Tardive dyskinesia (TD) is a potentially permanent and disabling adverse effect from certain medications. By definition TD is the insidious onset of rhythmic, repetitive, stereotypic movements of the face, mouth and tongue, often with involvement of the trunk and extremities that occur as a result of dopamine receptor blocking agents (DRBA) [1]. The term tardive refers to the delayed onset of the disorder. The mean prevalence of TD is estimated to be 25.3% in psychiatric patients taking antipsychotics [2]. Compared to the number of people taking these drugs, TD represents a minority. TD is a potentially permanent condition; stopping the offending agent does not always alleviate the condition. Therefore, prevention of TD by avoiding DRBA's if at all possible is ideal. However, there is no apparent way to predict who will develop TD and there are some cases in which DRBA's are necessary for treatment of chronic conditions. As TD has been present since the development of DRBA's, possible risk factors for its development have been studied. Solmi et al. (2018) [3] have written a comprehensive review on this subject.