Haem synthesis in sideroblastic anaemia

Area of Science:

• Biochemistry
• Hematology
• Genetics

Background:

• Sideroblastic anemia is a group of disorders characterized by impaired heme synthesis.
• Delta-aminolaevulinic acid (ALA) synthetase is a key enzyme in heme biosynthesis.
• Understanding enzyme activity is crucial for diagnosing and managing different subtypes of sideroblastic anemia.

Purpose of the Study:

• To measure delta-aminolaevulinic acid (ALA) synthetase activity in patients with various forms of sideroblastic anemia.
• To investigate the role of pyridoxal-phosphate in correcting enzyme deficiencies.
• To explore the heterogeneity of defects in heme synthesis in sideroblastic anemia.

Main Methods:

• Bone marrow samples were collected from normal subjects and patients with congenital, pyridoxine-responsive, primary acquired, and secondary sideroblastic anemia.
• ALA-synthetase activity was measured with and without added pyridoxal-phosphate in vitro.
• Haem synthetase activity and 14C-labeled ALA incorporation into heme were assessed in select cases.

Main Results:

• Reduced ALA-synthetase activity was observed in congenital and primary acquired sideroblastic anemia, with some cases responsive to pyridoxal-phosphate.
• Pyridoxine-responsive anemia showed normal ALA-synthetase activity during pyridoxine therapy, but deficiency upon withdrawal, suggesting an abnormal apoenzyme.
• Reduced haem synthetase activity and impaired ALA incorporation into heme were noted in some patients.

Conclusions:

• Sideroblastic anemias are heterogeneous disorders with diverse defects in heme synthesis.
• Reduced ALA-synthetase activity is common but not universal.
• Pyridoxine-responsive anemia may involve an abnormal ALA-synthetase apoenzyme with increased pyridoxal-phosphate requirements.