abnormal hydroxymethylbilane synthase activity decreased hydroxymethylbilane synthase activity MP:0020311 MPheno.ontology decreased (4-(2-carboxyethyl)-3-(carboxymethyl)pyrrol-2-yl)methyltransferase (hydrolyzing) activity decreased (4-[2-carboxyethyl]-3-[carboxymethyl]pyrrol-2-yl)methyltransferase (hydrolysing) decreased HMB synthase activity decreased HMB-synthase activity decreased porphobilinogen ammonia-lyase (polymerizing) decreased porphobilinogen deaminase activity decreased porphobilinogen:(4-[2-carboxyethyl]-3-[carboxymethyl]pyrrol-2-yl)methyltransferase (hydrolysing) decreased pre-uroporphyrinogen synthase activity decreased uroporphyrinogen I synthase activity decreased uroporphyrinogen I synthetase activity decreased uroporphyrinogen synthase activity decreased uroporphyrinogen synthetase activity reduced ability of to catalyze the reaction: H(2)O + 4 porphobilinogen = hydroxymethylbilane + 4 NH(4)(+).