A promoter mutation in the erythroid-specific 5-aminolevulinate synthase (ALAS2) gene causes X-linked sideroblastic anemia.
X-linked sideroblastic anemia (XLSA) is caused by mutations in the erythroid-specific 5-aminolevulinate synthase gene (ALAS2). XLSA was diagnosed in a 32-year-old woman with a mild phenotype and moderately late onset. Pyridoxine therapy had no effect in the proband, but in her affected son engendered a modest increase in hemoglobin concentration and a 4-fold reduction in ferritin iron. Molecular analysis identified a C to G transversion at nucleotide -206 from the transcription start site, as defined by primer extension, in the proximal promoter region of ALAS2. No other mutations were found in the promoter region, the flanking intronic sequences, the exons, or the 3' genomic region. The same mutation was found in her affected son but not in any other of her unaffected relatives. The mutation resulted in a 94% loss of activity relative to the wild-type sequence for a luciferase reporter construct containing the proximal 293 nucleotides (nt's) of the ALAS2 promoter when transfected into human erythroid K562 cells. Confirming the mutation's deleterious effect, the ALAS2 mRNA level in the proband's erythroid precursors was reduced 87%. The mutation occurred in or near 3 different putative transcription factor binding sites of unknown erythroid importance. The dramatic decreases in reporter activity and mRNA level suggest that the region of the mutation may bind a novel and important erythroid regulatory element.
Bekri
Soumeya
S
Department of Human Genetics, Mount Sinai School of Medicine, New York, NY, USA.
May
Alison
A
Cotter
Philip D
PD
Al-Sabah
Ala I
AI
Guo
Xiaojun
X
Masters
Gillian S
GS
Bishop
David F
DF
D000624:5-Aminolevulinate Synthetase / Q000235:genetics*; D000328:Adult; D000756:Anemia, Sideroblastic / Q000188:drug therapy / Q000201:enzymology / Q000235:genetics*; D001483:Base Sequence; D001665:Binding Sites; D004247:DNA / Q000235:genetics / Q000378:metabolism; D015672:Erythroid Precursor Cells / Q000378:metabolism; D005260:Female; D017930:Genes, Reporter; D040181:Genetic Diseases, X-Linked / Q000188:drug therapy / Q000201:enzymology / Q000235:genetics*; D000071020:Hemochromatosis Protein; D006454:Hemoglobins / Q000032:analysis; D015395:Histocompatibility Antigens Class I / Q000235:genetics; D006801:Humans; D007527:Isoenzymes / Q000235:genetics; D020014:K562 Cells / Q000378:metabolism; D008156:Luciferases / Q000096:biosynthesis / Q000235:genetics; D008297:Male; D008565:Membrane Proteins / Q000235:genetics; D008969:Molecular Sequence Data; D010641:Phenotype; D017354:Point Mutation; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011736:Pyridoxine / Q000627:therapeutic use; D012333:RNA, Messenger / Q000096:biosynthesis; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection
C103673:HFE protein, human; D000071020:Hemochromatosis Protein; D006454:Hemoglobins; D015395:Histocompatibility Antigens Class I; D007527:Isoenzymes; D008565:Membrane Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D004247:DNA; D008156:Luciferases; D000624:5-Aminolevulinate Synthetase; D011736:Pyridoxine