X-linked sideroblastic anemia due to ALAS2 intron 1 enhancer element GATA-binding site mutations

Abstract

X-linked sideroblastic anemia (XLSA) is the most common form of congenital sideroblastic anemia. In affected males, it is uniformly associated with partial loss-of-function missense mutations in the erythroid-specific heme biosynthesis protein 5-aminolevulinate synthase 2 (ALAS2). Here, we report five families with XLSA owing to mutations in a GATA transcription factor binding site located in a transcriptional enhancer element in intron 1 of the ALAS2 gene. As such, this study defines a new class of mutations that should be evaluated in patients undergoing genetic testing for a suspected diagnosis of XLSA.

Figure 1. XLSA pedigrees with GATA binding site mutations

A. Families A, F, and P are from the United States, N from the Netherlands, and C from Great Britain. The genotype or affected status of individuals studied are indicated by black shading. Individuals with inferred genotypes or phenotypes are shaded gray. An arrow indicates the proband in each family. *Indicates a clinically affected heterozygous female. B. Sequence shown is on the positive strand of the GRCh37/hg19 reference sequence: Chr X:55054622-55054649. This corresponds to g.7849 to g.7876 in the ALAS2 genomic sequence in the reverse orientation. The GATA binding site is underlined. The mutation in each family is in bold italics.

Figure 2. ALASS mRNA expression in GATA binding site mutated patients

Peripheral blood erythrocyte ALAS2 mRNA normalized to alpha hemoglogin stabilizing protein (AHSP) mRNA levels are shown in wild type control and patients with ALAS2 missense (ALAS2), SLC25A38, and ALAS2-GATA biding site mutations. Whisker plots indicate the mean ± one standard deviation. Data were qualitatively similar when ALAS2 levels were normalized to AHSP, β-actin, or SLC4A1 mRNAs.