Beta THALASSEMIA (23 Mutations)

Common beta‑thalassemia mutations are HBB gene point changes that disrupt splicing, translation or stability. Frequent examples include IVS‑I‑5 (G→C), IVS‑I‑1 (G→A), IVS‑II‑654 (C→T), codon 41/42 (−CTTT frameshift) and codon 39 (C→T) nonsense. Other pathogenic changes include promoter mutations, small deletions/insertions and occasional large deletions that reduce or abolish β‑globin production.

Thalassemia is caused by mutations in the globin genes that reduce or abolish production of alpha or beta hemoglobin chains. These include point mutations, splice‑site and promoter variants, small insertions/deletions and larger gene deletions. Alpha‑thalassemia commonly involves deletions of HBA1/HBA2, while beta‑thalassemia usually involves point or splice‑site mutations in HBB; inheritance is typically autosomal recessive.

"Cooley anemia" is named after American pediatrician Thomas B. Cooley, who in the 1920s first described the severe hereditary form of thalassemia in children. The eponym recognizes his identification of its clinical features—severe anemia, growth failure, and splenomegaly. Today this disorder is usually called beta‑thalassemia major, a genetic defect in hemoglobin production.

Beta-thalassemia is caused by mutations in the HBB gene on chromosome 11 that reduce or abolish beta‑globin production. Most are single‑base (point) changes, small insertions/deletions, or splicing and promoter defects that impair transcription or mRNA processing. These inherited autosomal recessive mutations produce imbalanced hemoglobin chain synthesis and result in varying severity of anemia.

The most common thalassemia mutation in India is the beta‑globin gene IVS‑I‑5 (G→C) splice‑site mutation. It is the predominant cause of beta‑thalassemia across many Indian populations, though frequencies vary regionally. Other recurrent mutations include codon 41/42, codon 8/9, and the 619 bp deletion, but IVS‑I‑5 remains the single most frequent defect.

A nonsense mutation is a single-base change in DNA that converts a codon for an amino acid into a stop codon. This causes premature termination of protein synthesis, producing a truncated, usually nonfunctional protein. Many nonsense mutations lead to loss of function and can cause genetic diseases; some transcripts are degraded by nonsense-mediated mRNA decay, reducing production of the faulty protein.