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Human leukocyte antigen (HLA) B27 (subtypes B*2701-2759) [1] is a class I surface molecule encoded by the B locus in the major histocompatibility complex (MHC) ...
All alleles start with "HLA", signifying they are part of the human MHC genes. The next portion (HLA-A or HLA-B) identifies which gene the allele is a modification of. The first two numbers (HLA-A*02) signifies what antigen type that particular allele is, which typically signifies the serological antigen present. [3]
An HLA haplotype is a series of HLA "genes" (loci-alleles) by chromosome, one passed from the mother and one from the father. The phenotype exampled above is one of the more common in Ireland and is the result of two common genetic haplotypes: A *01:01 ; C *07:01 ; B *08:01 ; DRB1 *03:01 ; DQA1 *05:01 ; DQB1 *02:01 (By serotyping A1-Cw7-B8-DR3-DQ2)
The most diverse loci, namely HLA-A, HLA-B, and HLA-C, have roughly 6000, 7200, and 5800 known alleles, respectively. [39] Many HLA alleles are ancient, sometimes of closer homology to a chimpanzee MHC alleles than to some other human alleles of the same gene. MHC allelic diversity has challenged evolutionary biologists for explanation.
HLA, the human form of the major histocompatibility complex (MHC), is located on chromosome 6 at 6p21.3. [11] Individuals inherit two different HLA haplotypes, one from each parent, each containing more than 200 genes relevant to helping the immune system recognize foreign invaders.
Closely related alleles are categorized together; for example, at least 28 very similar alleles are subtypes of HLA-B27. These subtypes are designated as HLA-B*2701 to HLA-B*2728. The HLA-B gene is located on the short (p) arm of chromosome 6 at cytoband 21.3, from base pair 31,353,871 to 31,357,211 [3]
Most of the gene defects are autosomal recessives, so that if both the mother and father carry the same defect, the chance that their child will have the associated disease is 1 in 4. The molecular genetics of many of these diseases have been determined, enabling genetic testing , prenatal testing , and counseling.
There is an association with the HLA-B27 histocompatibility antigen, which is present in 65% of patients with erythema nodosum. [19] A useful mnemonic for causes is SORE SHINS (Streptococci, OCP, Rickettsia, Eponymous (Behçet), Sulfonamides, Hansen's Disease (Leprosy), IBD, NHL, Sarcoidosis. [20]
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