鐮刀型紅血球疾病
Sickle cell disease

context: zh_tw: 因為脾臟細小的血管和負有清除不良紅血球的功能，所以常常會被影響到，通常在患者兒童期末期前便會形成梗塞。這種自體脾臟移除（autosplenectomy）會增加被 encapsulated organisms 感染的風險，對於這類脾功能缺乏者，預防性的抗生素和接種都被建議要有的。肝衰竭也有可能漸漸地出現。
en: Because of its narrow vessels and function in clearing defective red blood cells, the spleen is frequently affected. It is usually infarcted before the end of childhood in individuals suffering from sickle cell anaemia. This spleen damage increases the risk of infection from encapsulated organisms; preventive antibiotics and vaccinations are recommended for those lacking proper spleen function.
qas: question: zh_tw: 脾臟如何破壞細胞？
en: How does the spleen damage the cells?
answers: zh_tw: text: 增加被 encapsulated organisms 感染的風險
en: text: increases the risk of infection from encapsulated organisms

context: zh_tw: 通常人體內會存在由兩個 α 鏈、兩個 β 鏈組成的血紅蛋白 A，由兩個 α 鏈、兩個 δ 鏈組成的血紅蛋白 A2，以及由兩個 α 鏈、兩個 γ 鏈組成的血紅蛋白 F。其中，新生兒在六週以前，體內主要以血紅蛋白 F 為主，而出生六週以後則主要為血紅蛋白 A。在被診斷為鐮刀型紅血球疾病的患者中，至少一個複製的 β 珠蛋白被鐮刀型血紅蛋白 (Hb S) 替代。在最常見的鐮刀型紅血球疾病，即鐮狀紅血球貧血症患者中，兩個複製的 β 珠蛋白均被鐮刀型血紅蛋白 (Hb S) 替代。鐮刀型紅血球為常染色體隱形遺傳疾病。一個人從父母遺傳得到的血紅蛋白基因決定了他（她）血液中含有哪種血紅蛋白。如果父母二人中一人為鐮狀紅血球貧血患者，而另一人為鐮狀紅血球基因攜帶者，則子女有 50% 的機率患有鐮狀紅血球貧血疾病，50% 的機率為鐮狀紅血球基因攜帶者。如果父母二人均為鐮狀紅血球基因攜帶者，則子女有 25% 的機率患有鐮狀紅血球貧血疾病， 25% 的機率攜帶正常血紅蛋白基因，以及 50% 機率為鐮狀紅血球基因攜帶者瘧原蟲生活史會侵入紅血球中發育。瘧原蟲會導致鐮刀型紅血球過早破裂，使得瘧原蟲不能繁殖。此外，聚合的血紅素影響寄生蟲消化血紅素的能力。因此在瘧疾疫區，鐮狀紅血球基因攜帶者較容易存活。
en: Normally, humans have haemoglobin A, which consists of two alpha and two beta chains, haemoglobin A2, which consists of two alpha and two delta chains, and haemoglobin F, consisting of two alpha and two gamma chains in their bodies. Out of these three types, haemoglobin F dominates until about 6 weeks of age. Afterwards, haemoglobin A dominates throughout life. In people diagnosed with sickle cell disease, at least one of the β-globin subunits in haemoglobin A is replaced with what is known as haemoglobin S. In sickle cell anaemia, a common form of sickle cell disease, haemoglobin S replaces both β-globin subunits in the haemoglobin.Sickle cell conditions have an autosomal recessive pattern of inheritance from parents. The types of haemoglobin a person makes in the red blood cells depend on what haemoglobin genes are inherited from her or his parents. If one parent has sickle cell anaemia and the other has sickle cell trait, then the child has a 50% chance of having sickle cell disease and a 50% chance of having sickle cell trait. When both parents have sickle cell trait, a child has a 25% chance of sickle cell disease, 25% do not carry any sickle cell alleles, and 50% have the heterozygous condition.Sickle cell gene mutation probably arose spontaneously in different geographic areas, as suggested by restriction endonuclease analysis. These variants are known as Cameroon, Senegal, Benin, Bantu, and Saudi-Asian. Their clinical importance is because some are associated with higher HbF levels, e.g., Senegal and Saudi-Asian variants, and tend to have milder disease.The gene defect is a single nucleotide mutation (see single-nucleotide polymorphism – SNP) (GAG codon changing to GTG) of the β-globin gene, which results in glutamic acid (E/Glu) being substituted by valine (V/Val) at position 6. Haemoglobin S with this mutation is referred to as HbS, as opposed to the normal adult HbA. This is normally a benign mutation, causing no apparent effects on the secondary, tertiary, or quaternary structures of haemoglobin in conditions of normal oxygen concentration. However, under low oxygen concentration, HbS polymerizes and forms fibrous precipitates because the deoxy form of haemoglobin exposes a hydrophobic patch on the protein between the E and F helices (Phe 85, Leu 88).In people heterozygous for HbS (carriers of sickling haemoglobin), the polymerisation problems are minor because the normal allele is able to produce half of the haemoglobin. In people homozygous for HbS, the presence of long-chain polymers of HbS distort the shape of the red blood cell from a smooth doughnut-like shape to ragged and full of spikes, making it fragile and susceptible to breaking within capillaries. Carriers have symptoms only if they are deprived of oxygen (for example, while climbing a mountain) or while severely dehydrated.
qas: question: zh_tw: 人體通常有什麼？
en: What do humans normally have?
answers: zh_tw: text: α 鏈
en: text: haemoglobin A