Glycine loading test in acute intermittent porphyria patients and their relatives

The effect of glycine ingestion on the urinary excretion of delta-aminolevulinic acid (ALA) and porphobilinogen (PBG) was measured in 15 normal subjects (a group of patients with acute intermittent porphyria (AIP) in remission and their close relatives). In the patients with AIP and in one relative with latent porphyria, glycine loading evoked a significant increase in the urinary excretion of ALA and PBG. This response was not observed in any of the normal volunteers, relatives of the patients with AIP with normal basal values, or in four subjects with chronic liver disease. In one family with asymptomatic AIP, one member with normal baseline values responded to glycine, and four members with elevated basal levels of either ALA or PBG showed positive tests which reverted to normal in one on serial studies. The glycine loading test is useful in the diagnosis of AIP in remission but not for the detection of genetic carriers of the AIP trait.