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ALAD gene

aminolevulinate dehydratase

Normal Function

The ALAD gene provides instructions for making an enzyme known as delta-aminolevulinate dehydratase. This enzyme is involved in the production of a molecule called heme. Heme is vital for all of the body's organs, although it is found mostly in the blood, bone marrow, and liver. Heme is an essential component of several iron-containing proteins called hemoproteins, including hemoglobin (the protein that carries oxygen in the blood).

The production of heme is a multi-step process that requires eight different enzymes. Delta-aminolevulinate dehydratase is responsible for the second step in this process, which combines two molecules of delta-aminolevulinic acid (the product of the first step) to form a compound called porphobilinogen. In subsequent steps, four molecules of porphobilinogen are combined and then modified to produce heme.

Health Conditions Related to Genetic Changes


At least 10 mutations in the ALAD gene can cause a rare form of porphyria called ALAD deficiency porphyria. Most of these mutations change single protein building blocks (amino acids) in delta-aminolevulinate dehydratase. These changes reduce the activity of the enzyme, allowing delta-aminolevulinic acid to build up to toxic levels in the body. This compound is formed during the normal process of heme production, but reduced activity of delta-aminolevulinate dehydratase allows it to accumulate to toxic levels. Very high levels of this compound can cause attacks of abdominal pain, vomiting, and other signs and symptoms of ALAD deficiency porphyria.

More About This Health Condition

Other disorders

A common variation (polymorphism) in the ALAD gene may affect the risk of developing lead poisoning in people exposed to environmental lead. Lead is a heavy metal that is toxic when inhaled or ingested. Lead poisoning can cause significant health problems involving the nervous system, blood, kidneys, and reproductive system.

The ALAD variation that has been studied most extensively replaces the amino acid glycine with the amino acid cysteine at position 177 in delta-aminolevulinate dehydratase (written as Gly177Cys or G177C). This variation may influence the amount of lead in a person's blood and bones. Although some studies suggest that this variation increases the risk of lead poisoning, other studies have not found such an association.

Other Names for This Gene

  • 5-aminolevulinate dehydratase
  • 5-Aminolevulinate hydro-lyase (adding 5-aminolevulinate and cyclizing)
  • ALA-Dehydrase
  • Aminolevulinate Hydro-Lyase
  • aminolevulinate, delta-, dehydratase
  • Aminolevulinic Acid Dehydratase
  • delta-Aminolevulinate Dehydratase
  • delta-Aminolevulinic Acid Dehydratase
  • PBGS
  • Porphobilinogen Synthase

Additional Information & Resources

Tests Listed in the Genetic Testing Registry

Scientific Articles on PubMed

Catalog of Genes and Diseases from OMIM

Gene and Variant Databases


  • Akagi R, Kato N, Inoue R, Anderson KE, Jaffe EK, Sassa S. delta-Aminolevulinate dehydratase (ALAD) porphyria: the first case in North America with two novel ALAD mutations. Mol Genet Metab. 2006 Apr;87(4):329-36. doi: 10.1016/j.ymgme.2005.10.011. Epub 2005 Dec 15. Citation on PubMed
  • Akagi R, Nishitani C, Harigae H, Horie Y, Garbaczewski L, Hassoun A, Mercelis R, Verstraeten L, Sassa S. Molecular analysis of delta-aminolevulinate dehydratase deficiency in a patient with an unusual late-onset porphyria. Blood. 2000 Nov 15;96(10):3618-23. Citation on PubMed
  • Badminton MN, Elder GH. Molecular mechanisms of dominant expression in porphyria. J Inherit Metab Dis. 2005;28(3):277-86. doi: 10.1007/s10545-005-8050-3. Citation on PubMed
  • Jaffe EK, Stith L. ALAD porphyria is a conformational disease. Am J Hum Genet. 2007 Feb;80(2):329-37. doi: 10.1086/511444. Epub 2006 Dec 21. Citation on PubMed or Free article on PubMed Central
  • Jaffe EK. The porphobilinogen synthase catalyzed reaction mechanism. Bioorg Chem. 2004 Oct;32(5):316-25. doi: 10.1016/j.bioorg.2004.05.010. Citation on PubMed
  • Kauppinen R. Porphyrias. Lancet. 2005 Jan 15-21;365(9455):241-52. doi: 10.1016/S0140-6736(05)17744-7. Citation on PubMed
  • Kelada SN, Shelton E, Kaufmann RB, Khoury MJ. Delta-aminolevulinic acid dehydratase genotype and lead toxicity: a HuGE review. Am J Epidemiol. 2001 Jul 1;154(1):1-13. doi: 10.1093/aje/154.1.1. Citation on PubMed
  • Maruno M, Furuyama K, Akagi R, Horie Y, Meguro K, Garbaczewski L, Chiorazzi N, Doss MO, Hassoun A, Mercelis R, Verstraeten L, Harper P, Floderus Y, Thunell S, Sassa S. Highly heterogeneous nature of delta-aminolevulinate dehydratase (ALAD) deficiencies in ALAD porphyria. Blood. 2001 May 15;97(10):2972-8. doi: 10.1182/blood.v97.10.2972. Citation on PubMed
  • Sassa S, Akagi R, Nishitani C, Harigae H, Furuyama K. Late-onset porphyrias: what are they? Cell Mol Biol (Noisy-le-grand). 2002 Feb;48(1):97-101. Citation on PubMed
  • Scinicariello F, Murray HE, Moffett DB, Abadin HG, Sexton MJ, Fowler BA. Lead and delta-aminolevulinic acid dehydratase polymorphism: where does it lead? A meta-analysis. Environ Health Perspect. 2007 Jan;115(1):35-41. doi: 10.1289/ehp.9448. Citation on PubMed or Free article on PubMed Central

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.