Catalysis of the reaction: 5-hydroxy-6-methylpyridine-3,4-dicarboxylate + H+ = 5-hydroxy-6-methylpyridine-3-carboxylate + CO2.
3-hydroxy-2-methylpyridine-4,5-dicarboxylate 4-carboxy-lyase (3-hydroxy-2-methylpyridine-5-carboxylate-forming)