Understanding resistance to methadone treatment for opioid dependence

Methadone maintenance treatment (MMT) is the most widely-used therapy in opioid dependence, but it is not effective in some patients, who relapse or drop out from treatment. Researchers at the IMIM and Hospital del Mar led by Marta Torrens, in collaboration with colleagues at the CRG, have found a possible explanation of why some people may not respond well to this treatment.

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As the authors explain in their paper published this month in the journal European Neuropsychopharmacology, they carried out a genetic analysis on several patients, focusing on the gene ALDH5A1. This enzyme is involved in the catabolism of the neurotransmitter gamma-aminobutyric acid (GABA), the major inhibitory neurotransmitter in the mammalian central nervous system. ALDH5A1 comes in many forms, and the scientists found that subjects carrying the T variant allele had a higher risk to be nonresponders to methadone treatment. They hypothesized that this could be due to a reduction in the ALDH5A1 enzyme activity, which would increase endogenous GABA levels and therefore induce symptoms such as sedation and impaired psychomotor performance. These neuropsychological effects related with the reduction in enzyme activity could be responsible for a higher propensity to relapse in these genetically predisposed patients.

The findings could be helpful to predict which subjects with opioid dependence problems would probably not benefit from methadone maintenance treatment and could use other treatments instead, such as diamorphine.

Reference:

Fonseca F, Gratacòs M, Escaramís G, De Cid R, Martín-Santos R, Farré M, Estivill X, Torrens M. ALDH5A1 variability in opioid dependent patients could influence response to methadone treatment. Eur Neuropsychopharmacol. 2013 Oct 18;

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