C-terminal deletions in the ALAS2 gene lead to gain of function and cause X-linked dominant protoporphyria without anemia or iron overload

Am J Hum Genet. 2008 Sep;83(3):408-14. doi: 10.1016/j.ajhg.2008.08.003. Epub 2008 Sep 4.

Abstract

All reported mutations in ALAS2, which encodes the rate-regulating enzyme of erythroid heme biosynthesis, cause X-linked sideroblastic anemia. We describe eight families with ALAS2 deletions, either c.1706-1709 delAGTG (p.E569GfsX24) or c.1699-1700 delAT (p.M567EfsX2), resulting in frameshifts that lead to replacement or deletion of the 19-20 C-terminal residues of the enzyme. Prokaryotic expression studies show that both mutations markedly increase ALAS2 activity. These gain-of-function mutations cause a previously unrecognized form of porphyria, X-linked dominant protoporphyria, characterized biochemically by a high proportion of zinc-protoporphyrin in erythrocytes, in which a mismatch between protoporphyrin production and the heme requirement of differentiating erythroid cells leads to overproduction of protoporphyrin in amounts sufficient to cause photosensitivity and liver disease.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 5-Aminolevulinate Synthetase / genetics*
  • Chromosomes, Human, X / genetics*
  • Erythrocytes / metabolism
  • Female
  • Heme / metabolism
  • Humans
  • Male
  • Mutation
  • Porphyrias, Hepatic / genetics
  • Porphyrias, Hepatic / pathology*
  • Protoporphyrins / blood

Substances

  • Protoporphyrins
  • zinc protoporphyrin
  • Heme
  • 5-Aminolevulinate Synthetase
  • ALAS2 protein, human