Thalassemia 地中海型貧血

前言，hemoglobin的組成

Hb-A1: α2β2     Hb-A2: α2δ2(正常<3.5%)     Hb-F: α2γ2     Hb-H: β4     Bart's: γ4

α-thalassemia 
正常人有4個α globin genes (2條16號染色體上各有兩個α globin genes)
若失去任何正常的α globin gene就叫α-thalassemia

1. 失去1個α gene = silent α-thalassemia carrier (無症狀，做DNA分析才能偵測到)
2. 失去2個α gene = α-thalassemia minor, α-thalassemia trait (輕微貧血)
3. 失去3個α gene = α-thalassemia intermedia, HbH disease
4. 失去4個α gene = α-thalassemia major, hydrops fetalis，不會活

↑上圖來自成醫100級昱瑋所製作之ppt

HbH disease成因:

• Deletional: 3個deletion
• Non-deletional: 2個deletion + 1個mutation (ex Hemoglobin H constant spring)

Hemoglobin H constant spring

• The most common nondeletional α-thalassemic mutation
• An important cause of HbH disease in Southeast Asia
• Clinically severer than other HbH disease (growth delay, severe hemolysis, iron overload, requirement of transfusion)

β-thalassemia
正常人有2個β globin gene (兩條11號染色體上各1個)
若失去任何正常的β globin gene就叫β-thalassemia
症狀通常較α-thalassemia輕微

分類

1. β-thalassemia major:
   β(0) thalassemia or severely impaired beta globin production. 較嚴重，又稱Cooley's anemia, 1歲起會有貧血症狀、肝脾腫大、骨頭變形(bone marrow expansion)、Iron overload，可能死於青春期
2. β-thalassemia minor:
   有一個beta globin gene是好的，通常asymptomatic
3. β-thalassemia intermedia:
   嚴重度介於major及minor之間。有major的肝脾腫大、骨頭變形；但Hb還好，介於5~10之間，只有在infection時需要輸血。

另一種分類法：

• β(0) thalassemia: 無法製造任何beta globin
• β(+) thalassemia: 能製造beta globin，但產量減少