825380
Description
Flashcards by sophietevans, updated more than 1 year ago
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Created by sophietevans
over 10 years ago
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| Question | Answer |
| Which genetic event is involved in the aetiology of x-linked agammaglobulinaemia? | A mutation in Bruton's tyrosine kinase (BTK) gene. |
| What effect does the genetic event in x-linked agammaglobulinaemia have on B cells? | The BTK mutation results in pre-B cells failing to differentiate into mature B cells. |
| What is the inheritance pattern of XLA? | It is X-linked recessive, so it is predominately seen in males as they only have 1 copy of the X chromosome and therefore cannot use X-inactivation as females can. This pattern is used in the diagnostic differentiation between XLA, CVID, and Hyper IgM syndrome. |
| How does XLA present clinically? | As frequent and recurrent infections (otitis, sinusitis, pneumonia) - noticed in the first 5 years of life as the condition is genetic. |
| How is XLA diagnosed? | Blood screening identifying low serum IgG, IgA, and IgM (2 or more S.D. below the normal value for the individual's age) and low (<2%) CD19+ B cells in the peripheral blood is diagnostic of XLA, along with the inheritance pattern and infection history. |
| How is XLA treated? | Lifelong immunoglobulin replacement therapy (IRT), antibiotic courses for infections (potentially long term), and no vaccinations as IgG and IgM responses cannot be developed against the pathogens. |
| What genetic event results in common variable immunodeficiency (CVID)? | Mutations in the TACI alleles - the variations in the mutations result in the varied phenotypes seen, as there are 30-40 conditions under the CVID 'umbrella'. |
| What does the genetic event causing CVID do to B cells? | Mature B cells fail to differentiate into plasma cells and class switch. |
| How does CVID present clinically? | Frequent and recurrent viral/bacterial/fungal/protozoal infections, especially upper respiratory tract infections, and autoimmunity and allergies develop in ~20% of patients. This can include gastrointestinal disorders such as irritable bowel disease. |
| How is CVID diagnosed? | Blood screening reveals low serum IgG, IgM, and IgA, and there is a familial history of the disease affecting both males and females, unless the mutation is spontaneous. |
| How is CVID treated? | Lifelong immunoglobulin replacement therapy and antibiotic courses when necessary. |
| What is the cause of IgA deficiency? | The aetiology is unknown, but the result is that mature IgA B cells are unable to differentiate into plasma cells and secrete IgA. |
| How does IgA deficiency present clinically? | As frequent and recurrent urogenital, respiratory, and gastrointestinal infections, chronic diarrhoea, allergies and autoimmunity. The autoimmunity usually results in circulating levels of auto-organ antibodies being high, resulting in type 3 hypersensitivity reactions. Further, anti-IgA may be produced, resulting in transfusion reactions on receipt of blood products. Some patients may be asymptomatic as IgM 'compensates' for IgA. |
| How is IgA deficiency diagnosed? | Blood screens reveal low serum IgA (<7mg/dL) but normal levels of other immunoglobulins. |
| How is IgA deficiency treated? | There is no IgA replacement therapy available so long term courses of antibiotics are prescribed to treat the recurrent + frequent infections. |
| What mutation(s) result in Hyper IgM Syndrome? | Hyper IgM Syndrome can result from either a mutation in the B cell activation-induced cytidine-deaminase enzyme which occurs in both males and females, or from a mutation in the CD40 ligand on B cells, which is X-linked and thus predominately occurs in males. |
| What effect do the mutations in Hyper IgM Syndrome have on B cells? | Mature B cells are unable to class switch so only IgM is produced. |
| How does Hyper IgM Syndrome present clinically? | As recurrent sinopulmonary infections, and pneumonia caused by Pneumocystis carnii. Associated abnormalities include neutropenia and aplastic anaemia. |
| How is Hyper IgM Syndrome diagnosed? | Blood screens reveal low IgG/IgA/IgE but >200mg/dL IgM. The ultimate cause of it may be identified by analysing the inheritance pattern within a family. |
| What is the treatment for Hyper IgM Syndrome? | Lifelong immunoglobulin replacement therapy and antibiotic courses whenever these are necessary. |
| Why might XLA be masked for the first 6 months of life? | Because maternal antibodies delivered through the placenta protect the baby for this length of time. |
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