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first in order of importance; "the alpha male in the group of chimpanzees"; "the alpha star in a constellation is the brightest or main star"
the 1st letter of the Greek alphabet
the beginning of a series or sequence; "the Alpha and Omega, the first and the last, the beginning and the end"--Revelations
early testing stage of a software or hardware product; "alpha version"
an inherited form of anemia caused by faulty synthesis of hemoglobin (同)thalassaemia, Mediterranean_anemia, Mediterranean anaemia
any high mountain

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アルファ(ギリシア語アルファベットの第1字A,α;英語のA,aに相当) / アルファ星(星座の主星)
高山,高峰

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/01/20 13:52:12」(JST)

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Alpha-thalassemia (α-thalassemia, α-thalassaemia) is a form of thalassemia involving the genes HBA1^[1] and HBA2.^[2] Alpha-thalassemia is due to impaired production of 1,2,3, or 4 alpha globin chains, leading to a relative excess of beta globin chains. The degree of impairment is based on which clinical phenotype is present (how many chains are affected).

Epidemiology[edit]

The worldwide distribution of inherited alpha-thalassemia corresponds to areas of malaria exposure,^[3] suggesting a protective role for alpha-thalassemia against the more severe manifestations of malaria. Thus, alpha-thalassemia is common in sub-Saharan Africa, the Mediterranean Basin, the Middle East, South Asia, and Southeast Asia, and different genetic subtypes have variable frequencies in each of these areas.^[4] The epidemiology of alpha-thalassemia in the US reflects this global distribution pattern. The most common form of alpha(+) thalassemia seen in the US is due to the -alpha(3.7) deletion, a single alpha-globin gene deletion, and is present in approximately 30% of African Americans.^[5] However, even in the homozygous state this disorder will result only in a mild microcytic anemia. The more serious clinical disorders of Hb H and Hb Bart hydrops fetalis syndrome, although found throughout the US today, are more common in the Western US and have dramatically increased in prevalence in the past 2 decades due to increased Asian immigration.^[6]

Causes[edit]

It is most commonly inherited in a Mendelian recessive fashion. It is also connected to the deletion of the 16p chromosome.^{[citation needed]}

It can also be acquired, under rare circumstances.^[7] Due to the low occurrence of alpha-thalassemia, the disease can be mistaken for iron deficiency anemia.^[8]

Pathophysiology[edit]

α thalassemias result in decreased alpha-globin production, therefore fewer alpha-globin chains are produced, resulting in an excess of β chains in adults and excess γ chains in newborns. The excess β chains form unstable tetramers (called Hemoglobin H or HbH of 4 beta chains) which have abnormal oxygen dissociation curves. The excess γ chains form tetramers which are poor carriers of O₂ since their affinity for O₂ is too high so it is not dissociated in the periphery. Homozygote α⁰ thalassaemias, where there is lots of γ₄ but no α-globins at all (referred to as Hb Barts), often result in still birth.

Types[edit]

There are two genetic loci for α globin, and thus four genes in diploid cells. Two genes are maternal in origin and two genes are paternal in origin. The severity of the α thalassemias is correlated with the number of affected α globin genes: the greater, the more severe will be the manifestations of the disease.

When noting the genotype, a "-" indicates an absence of function, and a "α" indications a functional alpha chain. (In contrast to the "β^o" and "β⁺" notation used in beta-thalassemia, in alpha-thalassemia a distinction between absent and reduced function is not usually noted.)

Alleles affected	Description	Genotype
One	There is minimal effect. Three α-globin genes are enough to permit normal hemoglobin production, and there are no clinical symptoms. They have been called silent carriers. They may have a slightly reduced mean corpuscular volume and mean corpuscular hemoglobin.	-/α α/α
Two	The condition is called alpha thalassemia trait. Two α genes permit nearly normal erythropoiesis, but there is a mild microcytic hypochromic anemia. The disease in this form can be mistaken for iron deficiency anemia and treated inappropriately with iron. Alpha thalassemia trait can exist in two forms: alpha-thal-1 (αα/--), associated with Asians, involves cis deletion of both alpha genes on the same chromosome; alpha-thal-2 (α-/α-), associated with Africans, involves trans deletion of alpha genes on different (homologous) chromosomes.^[9]	-/- α/α or -/α -/α
Three	The condition is called Hemoglobin H disease. Two unstable hemoglobins are present in the blood: Hemoglobin Barts (tetrameric γ chains) and Hemoglobin H (tetrameric β chains). Both of these unstable hemoglobins have a higher affinity for oxygen than normal hemoglobin, resulting in poor oxygen delivery to tissues. There is a microcytic hypochromic anemia with target cells and Heinz bodies (precipitated HbH) on the peripheral blood smear, as well as splenomegaly. The disease may first be noticed in childhood or in early adult life, when the anemia and splenomegaly are noted.	-/- -/α
Four	The fetus cannot live once outside the uterus and may not survive gestation: most such infants are dead at birth with hydrops fetalis, and those who are born alive die shortly after birth. They are edematous and have little circulating hemoglobin, and the hemoglobin that is present is all tetrameric γ chains (hemoglobin Barts).	-/- -/-

References[edit]

^ Online 'Mendelian Inheritance in Man' (OMIM) 141800
^ Online 'Mendelian Inheritance in Man' (OMIM) 141850
^ Flint J, Hill AV, Bowden DK, et al. High frequencies of alpha-thalassaemia are the result of natural selection by malaria. Nature. 1986;321:744-750.
^ Bernini LF. Geographic distribution of alpha thalassemia. In: Steinberg M, Forget B, Higgs D, et al., eds. Disorders of hemoglobin. New York, NY: Cambridge University Press; 2001:878-894.
^ Beutler E, West C. Hematologic differences between African-Americans and whites: the roles of iron deficiency and alpha-thalassemia on hemoglobin levels and mean corpuscular volume. Blood. 2005;106:740-745.
^ Vichinsky EP, MacKlin EA, Waye JS, et al. Changes in the epidemiology of thalassemia in North America: a new minority disease. Pediatrics. 2005;116:818-825.
^ Steensma DP, Gibbons RJ, Higgs DR (January 2005). "Acquired alpha-thalassemia in association with myelodysplastic syndrome and other hematologic malignancies". Blood 105 (2): 443–52. doi:10.1182/blood-2004-07-2792. PMID 15358626.
^ http://www.cooleysanemia.org/updates/pdf/Alpha_Thalassemia.pdf
^ "Alpha Thalassemia Trait". St. Jude Children's Research Hospital. Retrieved 15 January 2014.

External links[edit]

GeneReviews/NCBI/NIH/UW entry on Alpha-Thalassemia
OMIM etries on Alpha-Thalassemia

UpToDate Contents

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1. サラセミアの臨床症状および診断 clinical manifestations and diagnosis of the thalassemias
2. αサラセミアの病態生理 pathophysiology of alpha thalassemia
3. サラセミア症候群の分子病理 molecular pathology of the thalassemic syndromes
4. 異型鎌状赤血球症候群 variant sickle cell syndromes
5. 鎌状細胞貧血における臨床的ばらつき clinical variability in sickle cell anemia

English Journal

Rapid detection of non-deletional mutations causing α-thalassemia by multicolor melting curve analysis.

Huang Q, Wang X, Tang N, Zhu C, Yan T, Chen P, Li Q.
Clinical chemistry and laboratory medicine.Clin Chem Lab Med.2016 Mar 1;54(3):397-402. doi: 10.1515/cclm-2015-0173.
BACKGROUND: α-Thalassemia, caused by mutations in the α-globin genes, is one of the most common monogenic inherited disorders in the world. However, non-deletional α-thalassemia mutations remain undetected in routine clinical testing due to the lack of a suitable method. In this study, a closed-
PMID 26351923

The Effect of Hydroxyurea Therapy in Bahraini Sickle Cell Disease Patients.

Shome DK1, Al Ajmi A2, Radhi AA3, Mansoor EJ3, Majed KS3.
Indian journal of hematology & blood transfusion : an official journal of Indian Society of Hematology and Blood Transfusion.Indian J Hematol Blood Transfus.2016 Mar;32(1):104-9. doi: 10.1007/s12288-015-0529-y. Epub 2015 Mar 18.
Hydroxyurea (HU) is used as a disease-modifying agent in sickle cell disease (SCD). Its beneficial effects have been ascribed to inhibition of the sickling process through increase of fetal hemoglobin (HbF) levels and influence on multiple factors affecting adhesion of erythrocytes to vascular endot
PMID 26855516

Evaluation of α-Globin Gene Mutations Among Different Ethnic Groups in Khuzestan Province, Southwest Iran.

Khosravi A1, Jalali-Far M2, Saki N2, Hosseini H2, Galehdari H2, Kiani-Ghalesardi O2, Paridar M3, Azarkeivan A4, Magaji-Hamid K5,6.
Hemoglobin.Hemoglobin.2016 Feb 15:1-5. [Epub ahead of print]
α-Thalassemia (α-thal) is one of the most common inherited hemoglobin (Hb) disorders in the world. In addition to large deletions, over 50 different α-thal point mutations were detected around the world, thus, patients showed different phenotypes with regard to genotype. This study evaluated the
PMID 26878087

Japanese Journal

αサラセミアによる胎児水腫を呈したベトナム人妊婦の一例

嶋田亜公子,矢木さやか,京谷琢治,高木剛,丸山憲一
日本周産期・新生児医学会雑誌 = Journal of Japan Society of Perinatal and Neonatal Medicine 48(3), 734-738, 2012-08-30
NAID 10031048871

Aortic Valve Replacement in a Patient with Alpha-Thalassemia

OMOTO Tadashi,TEDORIYA Takeo,KONDO Yasuyuki,IZUKA Hirofumi,OI Masaya,NAGANO Naoko,MIYAUCHI Tadamasa,ISHIKAWA Noboru,KASEGAWA Hitoshi
Annals of thoracic and cardiovascular surgery 16(5), 365-366, 2010-10-01
NAID 10029685909

心拡大と胎児水腫を呈した胎児αサラセミアの一例

久須美真紀,加藤有美,高橋宏典,三浦裕美子,林聡,大石芳久,高橋重裕,中村知夫,伊藤裕司,山口晃史,松岡健太郎,服部幸夫,山城安啓,左合治彦,北川道弘
日本周産期・新生児医学会雑誌 = Journal of Japan Society of Perinatal and Neonatal Medicine 44(4), 1241-1245, 2008-12-25
NAID 10025167361

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リンク元	「αサラセミア」「α地中海貧血症」「アルファサラセミア」
関連記事	「alpha」

「αサラセミア」

Alpha-thalassemia
	Classification and external resources
ICD-10	D56.0
ICD-9	282.43
OMIM	141800
DiseasesDB	448 33334, 33678
MeSH	D017085
GeneReviews	Alpha-Thalassemia;