HMBS（hydroxymethylbilane synthase），癌症关联基因，基因ID：3145，这个基因编码羟甲基双烷合酶超家族的一个成员。编码的蛋白质是血红素生物合成途径的第三种酶，催化四种恐孔素原分子的从头到尾缩合成线性羟甲基双烷。该基因突变与常染色体显性遗传病急性间歇性卟啉症有关。另外，还描述了编码不同亚型的剪接转录变体。[由RefSeq提供，2008年7月]This gene encodes a member of the hydroxymethylbilane synthase superfamily. The encoded protein is the third enzyme of the heme biosynthetic pathway and catalyzes the head to tail condensation of four porphobilinogen molecules into the linear hydroxymethylbilane. Mutations in this gene are associated with the autosomal dominant disease acute intermittent porphyria. Alternatively spliced transcript variants encoding different isoforms have been described. [provided by RefSeq， Jul 2008]。