12 Questions
What is the primary cause of the disease mentioned in the text?
Mutations in the gene encoding a kinase called Bruton tyrosine kinase (BTK)
What is the role of the enzyme Bruton tyrosine kinase (BTK) in pre-B cells?
It delivers signals that promote the survival, proliferation, and maturation of pre-B cells
Why are women who carry a mutant BTK allele on one of their X chromosomes considered carriers of the disease?
Because they can pass the mutated gene to their offspring
What is the name of the syndrome that results from incomplete development of the thymus and parathyroid glands?
DiGeorge Syndrome
What happens to patients with DiGeorge syndrome as they age?
Their condition improves with age
What has led to the recognition of mutations and other abnormalities in molecules involved in lymphocyte activation and function?
Better understanding of the molecules involved in lymphocyte activation and function
What percentage of X-linked SCID cases are caused by mutations in the common γ chain?
More than 99%
Which cytokine is the major growth factor for immature lymphocytes, especially pro-T cells?
Interleukin-7
What is the consequence of defective responses to IL-7 in humans?
Reduced T cell maturation
What is the name of the chain that is also called the IL-2Rγ chain?
Common γ chain
Which cells are affected in X-SCID, resulting in reduced survival and maturation?
Immature lymphocytes
What is the characteristic of SCID that affects only male children?
X-linked
Study Notes
Bruton Agammaglobulinemia
- Caused by mutations in the gene encoding Bruton tyrosine kinase (BTK)
- Results in defective production or function of the enzyme
- BTK is activated by the pre-B cell receptor expressed in pre-B cells
- The enzyme delivers signals that promote the survival, proliferation, and maturation of pre-B cells
- The BTK gene is located on the X chromosome
- Female carriers have a mutant BTK allele on one of their X chromosomes, but male offspring who inherit the abnormal X chromosome are affected
DiGeorge Syndrome
- Results from incomplete development of the thymus (and parathyroid glands)
- Patients fail to develop mature T cells
- The condition tends to improve with age, possibly due to the small amount of thymic tissue that develops
Defects in Lymphocyte Activation and Function
- Mutations and other abnormalities in molecules involved in lymphocyte activation and function can result in immunodeficiency disorders
- Examples include severe combined immunodeficiency (SCID) disorders
Severe Combined Immunodeficiency (SCID)
- Manifests as defects in both the B cell and T cell arms of the adaptive immune system
- Several different genetic abnormalities can cause SCID
- X-SCID is a type of SCID caused by γc mutations
- X-SCID affects only male children, accounting for about half of SCID cases
- More than 99% of X-linked SCID cases are caused by mutations in the common γ (γc) chain signaling subunit of the receptors for several cytokines
- The γc chain is necessary for immature lymphocytes, especially pro-T cells, to proliferate in response to IL-7
- Defective responses to IL-7 result in reduced survival and maturation of lymphocyte precursors
- In humans, the defect primarily affects T cell maturation
This quiz covers the genetic disorder caused by mutations in the BTK gene, leading to defective production or function of the Bruton tyrosine kinase enzyme. It affects the development and function of immune cells.
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