If you have samples you use frequently, such as reference samples or positive samples, we recommend you make aliquots and store them at -20°C. One aliquot at a time can then be stored at 4°C.
DNA is more stable when stored in TE0.1 (10 mM Tris-HCl pH 8.0 + 0.1 mM EDTA) than in water. TE0.1 is also more suitable for the MLPA reaction; see this article for more information.
Long-term storage at 4°C may degrade sample quality. Evaporation can increase the concentration of impurities, such as EDTA, which can inhibit the MLPA reaction. The growth of microorganisms can also degrade sample quality and introduce metabolites that can inhibit the reaction.