Acute intermittent porphyria (AIP), an autosomal dominant disorder, is divided into two forms, the classical form (more than 95%) and the non-erythroid variant form, according to erythroid porphobilinogen deaminase (PBGD) activity. In the variant form, the PBGD activity is essentially normal. Detection of presymptomatic mutation carriers relies on a DNA test. This variant form of AIP is very rare, with only nine families carrying five different mutations reported in the literature. Here we report a novel G-to-T transversion in the first position of intron 1 of the PBGD gene in a family with this variant form of AIP. We also review all previously reported cases and propose an effective diagnostic approach.