A Novel ALAS2 Mutation Causes Congenital Sideroblastic Anemia 

Yuxi Ding1,*, Kun Yang1,*, Xiaodong Liu1, Jian Xiao1, Wanting Li1 and Huixiu Zhong2.

Department of Hematology, Zigong First People's Hospital, Zigong, China.
2 Department of Laboratory Medicine, Zigong First People's Hospital, Zigong, China.
* This author equally contributed to this work.

Correspondence to: Kun Yang, Department of Hematology, Zigong First People's Hospital, Zigong, China; ORCID: 0000-0002-8619-9676, E-mail: 1759874951@qq.com

Published: November 01, 2023
Received: September 06, 2023
Accepted: October 16, 2023
Mediterr J Hematol Infect Dis 2023, 15(1): e2023062 DOI 10.4084/MJHID.2023.062

This is an Open Access article distributed under the terms of the Creative Commons Attribution License
https://creativecommons.org/licenses/by-nc/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

To the editor

Congenital sideroblastic anemias (CSAs) are inherited diseases of mitochondrial dysfunction due to defects in heme biosynthesis, iron-sulfur cluster biogenesis, generalized mitochondrial protein synthesis, or the synthesis of specific mitochondrial proteins involved in oxidative phosphorylation.[1] CSAs are characterized by the accumulation of ring sideroblasts in the bone marrow, with ineffective erythropoiesis and increased serum and tissue iron levels. X-linked sideroblastic anemia (XLSA) is the most common form of CSA and is attributed to 5-aminolevulinate synthase (ALAS2) mutations.[2] Here, we presented a de novo mutation in ALAS2 in a Chinese patient with CSA and a good response to pyridoxine treatment.
The proband was a 32-year-old female who was the family's only child. The family history was unremarkable, and the parents were non-consanguineous. At age 27, the proband required blood transfusions during her first pregnancy due to severe anemia. At that time, due to the low level of vitamin B12, the proband was incorrectly diagnosed with megaloblastic anemia.
At age 32, the proband again developed severe anemia during her second pregnancy and required a blood transfusion. Physical examination revealed that the spleen of the proband was enlarged to 5 cm below the costal margin. A hemogram at presentation to our center revealed a hemoglobin level of 5.9 g/dL (reference value: 12.0–15.0 g/dL), a red blood cell count of 1.41×1012/L (reference value: 3.8–5.1×1012/L), a mean corpuscular volume of 127.7 fL (reference value: 80–100 fL), mean corpuscular hemoglobin of 41.8 pg (reference value: 27–34 pg), a mean corpuscular hemoglobin concentration of 32.8 g/dL (reference value: 31.6–35.4 g/dL), a reticulocyte percentage of 2.35% (reference value: 0.5–1.5%), a white blood cell count of 3.95×10
9/L (reference value: 3.5–9.5×109/L), and a platelet count of 132×109/L (reference value: 100–300×109/L). A peripheral blood smear was dimorphic, including microcytic hypochromic, normocytic, and normochromic erythrocytes (Figure 1A). Serum biochemical tests revealed a total bilirubin level of 15 μmol/L (reference value: 0–23 μmol/L), an indirect bilirubin level of 8.7 μmol/L (normal range: 5–18 μmol/L), and a lactate dehydrogenase level of 117 U/L (reference value: 120–250 U/L). Iron metabolism testing revealed that serum ferritin, serum iron, and transferrin were 751.4 ng/mL (reference value: 4.63–204 ng/mL), 37.18 μmol/L (reference value: 7–30 μmol/L), and 1.57 g/L (reference value: 1.7–3.4 g/L), respectively. Levitt’s CO breath test showed that the erythrocyte life span of the proband was 24 days (normal range: 70–140 days). Laboratory tests for megaloblastic anemia, autoimmune hemolytic anemia, paroxysmal nocturnal hemoglobinuria, glucose-6-phosphate dehydrogenase deficiency, thalassemia, and hepatopathy were negative.
Next-generation sequencing of the proband and her family was carried out to investigate underlying variants associated with anemia in the proband. A de novo heterozygous missense mutation of ALAS2: c.1439G>A was found and further confirmed by Sanger sequencing (Figure 1B). The c.1439G>A mutation led to a substitution of a conserved arginine to histidine at residue 480 (p.Arg480His) in exon 9 of the ALAS2 protein. Given the ALAS2 mutation, a diagnosis of CSA was suspected.
Bone marrow analysis revealed marked erythroid hyperplasia with increased pronormoblast and basophilic erythroblast (Figure 1C). In Prussian blue-stained specimens, a bone marrow smear showed erythroid hyperplasia with a 66% proportion of total sideroblasts, and the proportion of ring sideroblasts was 16% (Figure 1D). Chromosome analysis revealed a normal karyotype (46, XY). A bone marrow biopsy showed hyperactive hyperplasia and no increase in reticulin fibers (MF0). Following the diagnosis of SA in the bone marrow, further investigations were conducted, including tests for pyridoxine, zinc, lead, and copper levels and chromosomal microarray analysis for myelodysplastic syndromes. All tests came back normal. The proband was thus diagnosed with CSA caused by this mutation of the ALAS2 gene. The proband had a good response to pyridoxine treatment, but her ferritin level gradually rose to 925.85 ng/mL.

Figure 1
Figure 1. A. The peripheral blood film from proband showed microcytic hypochromic, normocytic, and normochromic erythrocytes. B. Sanger sequencing 
revealed a novel heterozygous ALAS2 missense mutation detected in the proband, whereas the wild-type genotype was observed in her parents. C. Bone 
marrow analysis revealed marked erythroid hyperplasia with increased pronormoblast and basophilic erythroblast. D. Prussian blue-stained specimens 
of bone marrow film from the proband showed ringed sideroblasts with multiple perinuclear iron granules. 

XLSA typically affects younger males due to an X-linked recessive pattern of inheritance. However, as a result of familial-skewed inactivation of the normal X chromosome, females with ALAS2 mutations may have a late-onset clinical phenotype, as with the proband in this study.[3] The management of CSA remains primarily supportive rather than definitive. ALAS2 catalyzes the first step of the heme biosynthetic pathway by condensing glycine and succinyl-CoA to form delta-aminolevulinic acid in the presence of pyridoxal 5’-phosphate, which is the metabolite of vitamin B6.[4] Pyridoxine can enhance the activity of the ALAS2 enzyme, and more than half of XLSA patients are responsive to supplementation with pyridoxine.[5] More than 100 distinct mutations in the ALAS2 gene have been reported. Most disease-associated variants occur in exons 5 and 9; the latter contains the pyridoxal-binding amino acid.[2] This finding was confirmed by the good response to pyridoxine treatment observed in the proband.
Patients with CSA are prone to iron overload, whether pyridoxine-responsive or not, regardless of red blood cell transfusions. Iron overload is partly attributed to reduced hepcidin level secondary to ineffective erythropoiesis, which promotes intestinal iron absorption.[6] The ferritin level of our reported XLSA patient increased gradually. It is therefore necessary to monitor regularly patients' clinical, laboratory, and radiological parameters to detect these long-term complications. Anecdotal reports of hematopoietic stem cell transplantation in CSA describe effective remission.[7] However, early diagnosis and management of CSA remain fundamental, especially as iron overload should be kept at a minimum to ensure a better outcome of a potential future transplantation. Additionally, developing definitive treatments for CSA is an area of need. Preclinical studies and clinical trials are essential to determine whether novel agents such as luspatercept or approaches involving gene therapy for CSA would benefit its treatment.[8]
In conclusion, we identified a novel ALAS2 missense mutation causing CSA in the Chinese population. Our findings will provide valuable insights to broaden the clinical phenotypic spectrum of CSA and improve understanding of ALAS2 gene variants.


We thank the proband and her family members for their continuous support and participation in this study.


This study was financially supported by the Key Science and Technology Project of Zigong (grant nos. 2020YXY04).

Ethics approval

The study protocol was approved by the Medical Ethics Committee of the First People’s Hospital of Zigong.

Informed consent

 Written informed consent was obtained from the participating family.


  1. Fleming MD. Congenital sideroblastic anemias: iron and heme lost in mitochondrial translation. Hematology Am Soc Hematol Educ Program. 2011;2011:525-31. https://doi.org/10.1182/asheducation-2011.1.525 PMid:22160084  
  2. Ducamp S, Fleming MD. The molecular genetics of sideroblastic anemia. Blood. 2019;133:59-69. https://doi.org/10.1182/blood-2018-08-815951 PMid:30401706 PMCid:PMC6318428  
  3. Cazzola M, May A, Bergamaschi G, Cerani P, Rosti V, Bishop DF. Familial-skewed X-chromosome inactivation as a predisposing factor for late-onset X-linked sideroblastic anemia in carrier females. Blood. 2000;96:4363-5. https://doi.org/10.1182/blood.V96.13.4363 PMid:11110715  
  4. Shoolingin-Jordan PM, Al-Daihan S, Alexeev D, Baxter RL, Bottomley SS, Kahari ID, Roy I, Sarwar M, Sawyer L, Wang SF. 5-Aminolevulinic acid synthase: mechanism, mutations and medicine. Biochim Biophys Acta. 2003;1647:361-6. https://doi.org/10.1016/S1570-9639(03)00095-5 PMid:12686158  
  5. Bottomley SS, Fleming MD. Sideroblastic anemia: diagnosis and management. Hematol Oncol Clin North Am. 2014;28:653-70, v. https://doi.org/10.1016/j.hoc.2014.04.008 PMid:25064706  
  6. Furuyama K, Kaneko K. Iron metabolism in erythroid cells and patients with congenital sideroblastic anemia. Int J Hematol. 2018;107:44-54. https://doi.org/10.1007/s12185-017-2368-0 PMid:29139060
  7. Kim MH, Shah S, Bottomley SS, Shah NC. Reduced-toxicity allogeneic hematopoietic stem cell transplantation in congenital sideroblastic anemia. Clin Case Rep. 2018;6:1841-4. https://doi.org/10.1002/ccr3.1667 PMid:30214775 PMCid:PMC6132150  
  8. Van Dijck R, Goncalves Silva AM, Rijneveld AW. Luspatercept as Potential Treatment for Congenital Sideroblastic Anemia. N Engl J Med. 2023;388:1435-6. https://doi.org/10.1056/NEJMc2216213 PMid:37043658