Alad, also known as delta-aminolevulinic acid dehydratase, is involved in the synthesis of haem. It catalyzes the second step in the heme biosynthesis pathway, which is crucial for various biological processes such as oxygen transport and energy metabolism [2,6].

ALAD porphyria is an autosomal recessive disorder caused by a homozygous ALAD deficiency. Patients with this disorder excrete a large amount of ALA but not PBG into urine, and symptoms are similar to AIP but can be differentiated by inheritance pattern, PBG production, and ALAD activity [1].

The ALAD gene is polymorphic, with alleles δ-ALAD-1 and δ-ALAD-2 producing different phenotypes. The δ-ALAD-2 allele may be linked to high lead concentration in the body, and there are debates on whether it provokes or reduces lead toxicity [2]. Some studies have found associations between ALAD SNPs and lead or mercury levels in pregnant women and their newborns [3]. In Mexican children, ALAD genotype may be a susceptibility factor for the effects of lead on child growth [5]. In hepatocellular carcinoma, low expression of ALAD is correlated with poor prognosis [4].

In conclusion, Alad is essential for heme synthesis. Studies related to its polymorphism and deficiency have revealed its role in porphyria, lead-related health issues, and cancer prognosis. These findings from various research models contribute to understanding the biological functions of Alad and its implications in different disease conditions.