Test Your Knowledge of Severe Combined Immunodeficiency (SCID) Types

Study Notes

Classification of Severe Combined Immunodeficiency (SCID)

SCID is a group of genetic disorders that result in the absence or dysfunction of T, B, and/or NK cells, leading to severe immune deficiency.
X-linked SCID is caused by defects in the common gamma chain of the interleukin receptor, resulting in the inhibition of both T and NK cell development and a T−NK− phenotype. B cells counts vary from normal to high, but function is impaired.
Autosomal recessive SCID can be caused by JAK3 or CD25 deficiency, resulting in a T−B+NK− phenotype similar to X-linked SCID.
ADA deficiency and PNP deficiency are purine metabolism disorders that result in the accumulation of toxic metabolites, leading to a decrease in T, B, and NK cells and a T−B−NK− phenotype. ADA-SCID is more common than PNP-SCID.
Reticular dysgenesis is a rare form of SCID caused by the defect in mitochondrial adenylate kinase 2, leading to the accumulation of toxic metabolites that affect all hematopoietic stem cells, resulting in a T−B−NK− phenotype along with granulocytopenia and deafness.
Defects in V(D)J recombination, which affect lymphocyte antigen receptor rearrangement, result in a T−B−NK+ phenotype.
RAG1 and RAG2 enzymes help mediate double-strand DNA breakage recombination sites, and their deficiency results in cleavage defects during V(D)J recombination. Mutations in these genes can also cause Omenn syndrome, a type of leaky SCID.
Mutations in Artemis, DNA ligase IV, and Cernunnos/XLF genes also result in failure to resolve hairpins during V(D)J recombination, leading to a T−B−NK+ phenotype and radiosensitivity.
Specific inhibition of T cell development can result in a T−B+NK+ phenotype.
IL7α deficiency is a common form of SCID, as IL 7 provides survival and proliferative signals for early T cell development.
Mutations in CD45, CD3ε, CD3δ, and Orai 1 result in an absence of T cells, while NK cells are normal. B cells can be normal or reduced.
CORO1a gene defect leads to Coronin-1A deficiency, which is essential for T cell egression from the thymus. CORO1a deficiency results in a T−B+NK+ phenotype with the presence of the thymus.

Description

Do you know the different types of Severe Combined Immunodeficiency (SCID)? Test your knowledge with this quiz! From X-linked SCID to ADA deficiency and V(D)J recombination defects, this quiz will challenge you to identify the causes and resulting phenotypes of various forms of SCID. Brush up on your understanding of immunodeficiency disorders and see how many you can correctly identify.