Hemoglobin Bart's fetalis syndrome

**Definition:** Hb Bart's hydrops fetalis (HBFS) is the most severe form of alpha-thalassemia and is almost always lethal. It is characterised by fetal onset of generalised oedema, pleural and pericardial effusions, and severe hypochromic anaemia. HBFS can be caused by either homozygous or compound heterozygous alpha0 (alpha zero) thalassaemia, resulting in zero functional alpha haemoglobin genes.

**Long definition:** Homozygous or compound heterozygous alpha⁰ thalassaemia refers to a genetic condition where a person has no functional alpha-globin genes due to either: Homozygosity for an alpha⁰ (α⁰) deletion, or Compound heterozygosity for two different alpha⁰ deletions.

α⁰ (alpha-zero) thalassaemia means both alpha-globin genes on one chromosome are deleted: written as: (-) So: Homozygous alpha⁰ thalassaemia = (-/-) resulting in no functional alpha-globin genes at all.

Compound heterozygous alpha⁰ thalassaemia = (-/-), but each - comes from a different deletion or mutation, still results in complete loss of alpha-globin production.