Hb Constant Spring and Its Combinations with Other Forms of Thalassemia or Hemoglobinopathy in Northern Thailand

Hemoglobin Constant Spring (Hb CS; HBA2: c.427T>C) is a prevalent non-deletional α-thalassemia mutation frequently observed in Southeast Asia, particularly in Thailand. Given its clinical severity, especially when homozygous (αCSα/αCSα) or coinheritance with α⁰-thalassemia (αCSα /--) called Hb H-CS disease. Thus, early and accurate detection of Hb CS carriers is critical. However, routine laboratory screening can be challenging due to the low levels of Hb CS in heterozygous individuals. This study aimed to examine Hb CS and its combinations with other forms of thalassemia or hemoglobinopathies in Northern Thailand using a targeted next-generation sequencing (NGS). Hemoglobin analysis was routinely performed using high-performance liquid chromatography (HPLC) and/or capillary electrophoresis (CE) techniques. The α0-thalassemia --SEA, --THAI, and --Chiang Rai type deletions were identified using real-time polymerase chain reaction (PCR) combined with high-resolution melting (HRM) analysis. The Hb CS mutation was identified in 147 out of 2,773 samples (5.3%). The study consisted of 17 distinct genotypes in which revealed variability in clinical and hematological characteristics based on their combinations. Therefore, the identification of Hb CS is certainly useful in thalassemia screening, genetic counselling, control, prevention, and treatment.